Compass Xpress 800-476-9886 | 608-227-3000 | Fax: 608-831-1890
Monday - Friday 9:00 - 5:30 CST

Full Compass Systems 800-356-5844 | 608-831-7330 | Fax: 608-831-6330
Monday - Friday 9:00 - 5:30 CST
¡Expertos que hablan Español disponibles en x1178 Y x1164!

Pro Audio Questions & Answers

We've gathered all this useful info just for you:

General Audio Questions and Answers:

  • Q: Why should I use anything other than a cardioid microphone? [Answer]
  • Q: What is the real difference in audio cable? [Answer]
  • Q: What is phantom power? [Answer]
  • Q: Is there an advantage to using an unidirectional lavalier microphone instead of an omnidirectional lavalier microphone? [Answer]
  • Q: What is proximity effect? [Answer]
  • Q: Why can't I use more than one microphone at a time on my wireless system? [Answer]
  • Q: Why doesn't my microphone work with my DAT recorder? It has the right connectors. [Answer]

Microphones

Wireless Microphones

Recording

Speakers

Headphones

Amplifiers

Equalizers, Etc.

Power Distribution

Computer Related

Other Resources:

Shure Publications:

Why should I use anything other than a cardioid microphone?

Most microphones on the market are Cardioid, Supercardioid or Hypercardioid. Is more better?

The most basic type of microphone is the Omnidirectional microphone. The omni is probably the most accurate and desirable type to use if feedback or isolation is not a problem. Getting close to the instrument to be miked is often all that is needed to isolate it from other sounds. Also consider that, when placing a cardioid mic in front of a hard surface like that of a drum or cymbal, the mic will pick up sound from the rear as a reflection from the surface, the mic is no longer cardioid, use an omni!

A Figure-8 microphone can cancel out sound from the side better than any cardioid can from the rear. A good example would be a person singing and playing acoustic guitar. Use two Figure-8s and put the voice off axis on the guitar mic and visa-versa for the voice mic. Another example would be two persons singing into one mic, place them on either side and get great isolation.

Is a cardioid mic is good, is a super or hypercardioid better? In some feedback situations, less is more. The cardioid rejects the most sound at the rear. The hypercardioid rejects sound from the rear and actually picks up more sound from the rear than a cardioid, but less sound from the side.

Back to top

What is the real difference in audio cable?

Much of the difference is in ruggedness and in the quality of shielding. Speaker cable should not be shielded, but all microphone and line level cables must be shielded. Some shields are less than 100%, some are braided for flexibility and others are foil for permanent installations. The quality of the connectors, connections and raw materials determine whether the cable can be used in a harsh environment. The connector quality is important if the cable will be reconnected often or seldom.

There are visible differences in video cables, but those differences are quantifiable in specifications such as impedance, velocity, capacitance, dielectric loss, and shielding quality.

The sad truth is that much esoteric cable is designed on "faith," without any real specifications or measurements of quality.

On the humorous side are dealers who offer, for an added fee, to "break in " cable for their customers. We suppose that if you are going to buy into the myth, you might as well go all the way and loosen up those sticky electrons.

Back to top

What is phantom power?

Modern condenser microphones have miniature preamps built into their cases which require DC power to operate (usually between 12 and 52 volts). Phantom power is a method of applying that power through the microphone cable from a remote supply. This supply can be a stand alone unit or may be incorporated in the audio mixer. It's called phantom power because it comes from outside the microphone and is not supplied from an internal battery. Plugging a dynamic microphone into a mixer that has phantom power will not damage the microphone as long as you are using a balanced microphone. If you connect an unbalanced microphone to an input that is supplying phantom power, you may hear a steady hum or buzz.

Phantom power is sometimes called simplex power, which is the same thing. There is also a different type of power used in some European microphones call AB power or T power. Phantom power mics will not operate with AB power or vise versa. The two types of voltages are electrically incompatible. Also, some phantom power mics must have at least 48v DC to operate and some will not handle more than 12 v DC or it will damage the microphone. If in doubt check the specifications or consult your Full Compass representative.

Some of the Phantom power supplies represented by Full Compass are Stewart, AKG, Electro Voice, Crown and Audio-Technica.

Back to top

Is there an advantage to using an unidirectional lavalier microphone instead of an omnidirectional lavalier microphone?

In some applications, mostly micing instruments, the unidirectional mic could be desirable since they help in reducing feedback and can increase system gain. For most applications though, the effect is overrated, and an omnidirectional mic is a better choice.

Omnidirectional mics offer several advantages. They will not emphasize the already resonant chest cavity on a person because they don't have proximity effect, and can be clipped on in different ways without changing the sound quality. The frequency response on an omnidirectional mic is always more uniform.

Some of the lavalier mics represented by Full Compass are made by Audio Technica, Sennheiser, Sony, Beyer Dynamic and Countryman.

Back to top

What is proximity effect?

Proximity effect is an increase in low frequency response when a microphone is very close to the sound source, and is an inherent characteristics of direct tonal microphones. Omnidirectional mics do not exhibit this effect and variable D mics (like the EV RE20) can limit the proximity effect.

Back to top

Why can't I use more than one microphone at a time on my wireless system?

The customer bought a handheld mic to add on to their existing wireless lavelier system and wanted to use both at the same time.)

Actually, you need two systems to use two mics in a wireless system because the microphone is the transmitter. A wireless system is a small scale version of a typical commercial FM broadcasting system. You have a transmitter and a receiver. The transmitter and receiver are tuned to a particular frequency. The receiver must be tuned to that frequency to hear that transmitter. Remember the mic is the transmitter. So if you want to use two transmitters (mics) to one receiver you must totally power down the mic you are not using. Otherwise there will be interference between the two mics. The same as when you are in your car between two radio stations on the same frequency. The stronger signal will overpower the weaker signal. And until you are totally out of range of one or the other they will interfere with each other. If you are now totally confused call your Full Compass salesperson!

Some of the wireless microphones that Full Compass represents are Shure, Audio Technica, Samson, Telex, Sony and Vega.

Back to top

Why doesn't my microphone work with my DAT recorder? It has the right connectors.

Just because it has the right connectors doesn't mean it does what you would expect. Most DAT's use XLR connectors, because they have a balanced input and output section. To plug a microphone into most DAT's requires a microphone preamplifier. A microphone by itself doesn't have much output and requires some extra amplification to give the DAT recorder the correct level of sound it requires.

Some of the mic pro amplifiers Full Compass represents are Aphex, Rand, ART Focusrite, Symetrix and TH Audio.

Back to top

Boundary Microphones

Designed to be used flush with surfaces such as floors, walls, ceilings or tables, boundary microphones eliminate much of the combined filtering effects exhibited byplacing a conventional microphone near a hard surface. In the correct situations these mics can produce better articulation, less feedback and more natural overall sound. Popular applications include conference recording by placing on tables or ceilings, concert recordings when placed on the stage, stage dramatic recording or reinforcement when placed on the stage, studio recording from floor or wall placement and grand piano when taped to the underside of the lid.

Back to top

Condenser Microphones

Most modern condenser microphones have diaphragms under 1/2" in diameter. Thus size seems to offer the most accurate frequency response and off-axis uniformity. Small diaphragm mics are available in a wide range of prices and configurations. Some designs are modular in that different pattern capsules (or heads) can be fitted to the preamp body to create a wide variety of systems. Some modular systems offer extension cables, extension tubes and pivots to couple the capsule to the preamp; call us for details and available accessories. The models that use electret (permanently charged) elements are available that use either internal battery or external phantom power of 10 to 50 volts. The regular condensers usually will only operate from a 48 volt phantom supply.

Back to top

Dynamic Microphones

Dynamic microphones are the simplest and most rugged of all microphones, needing no power from batteries or external sources; they generate their own signal with few moving parts. The two types are the moving coil which works like a miniature loudspeaker in reverse, and the ribbon which exhibits low mass similar to condensers but has lower output voltage. Unlike condensers which have internal amplifiers which limit the loudness of the source sound, dynamics have no problems reproducing loud sounds such as drums or starter pistols. Few dynamics exhibit the ultra flat response of condensers, but most have a response curve tailored to enhance particular sounds, voices, and instruments.

A new kind of dynamic mic uses a new kind of magnetic structure made of Neodymium. These magnets are 4 times as powerful as conventional magnets meaning that the microphones using them can have higher output levels, better linearity and lower magnet mass allowing more compact microphone designs.

Back to top

Headphone Mics

When you need both hands free and a lapel microphone won't give enough volume before feedback, a head-mic is the answer.

A head mic puts the microphone where it does the most good, in front of the mouth; great for musicians who must sing, aerobic instructors, teachers, lecturers and tour guides. Most models have electret condenser microphones which need either battery or phantom power. A few models use dynamic elements which need no external power. All models can be adapted for use with wireless microphones for those users who need maximum mobility.

Back to top

Interview Microphones

Interview microphones are designed to be handheld by the interviewer so that both the interviewer and subject can use the same microphone. When interviewing it is normal for the interviewer to point the microphone towards the subject to indicate when it is time for them to talk. Since both people may talk whichever way the microphone is pointed, most interview mics are omnidirectional. Some models have an extra long handle for more comfortable positioning, some have extra internal shockmounting to reduce handling noise. A few are directional for use in high-noise environments. Most have the frequency response tailored to enhance voice pickup and reduce background noises.

Back to top

Lapel Mics

What has great aesthetics and terrible acoustics? Under the chin and against the chest is a terrible place to attach a microphone from an acoustic point of view. Very little of the clarity and volume of the voice makes it down that way. Most lapel microphones try to compensate for their disadvantaged response.

So little of the voice makes it down to the lapel mic that mixer volume must be boosted to make up the difference. While this can be a problem when used for sound reinforcement, it's no problem for recording, video, interviewing and broadcasting. Many people find them prone to feedback when used in front of or under speakers.

Most lapel mics are condenser; condensers can be made much smaller than dynamic mics. Condensers do need either battery or phantom power. The general rule is the smaller the mic, the higher the price.

Most lapel mics are omni-directional, which makes their placement less critical. Some models are available which are cardioid or bi-directional, these can improve isolation and reduce feedback problems, but their placement on the person is more critical.

The usual placement is on the lapel, tie, shirt or hidden in the clothes. For theater and entertainment, mics are sometimes placed in the hair if no clothing is convenient. Most models are available for use with wireless microphones.

Most of the condenser models have a battery compartment at the end of the cable attached to the connector. Useful accessories include spare clips and windscreens, since these are easily lost.

Back to top

Large Diaphragm Condenser Mics

Historically, large diaphragm condenser microphones date back to the 1920's and 1930's with diaphragms diameter in the one inch range. Although not the most accurate off-axis, they have kept a reputation for desirable sound, warmth and intimacy that is hard to find with other designs. Unfortunately these designs are much more expensive to build than most modern microphones. Many of the large diaphragm models feature dual back-to-back diaphragms which can be switched between Omni, Cardioid, and figure-8 patterns. The cardioid pattern is most often used for solo vocals and general instrument applications, the omni pattern is good for vocal groups in a circle around the mic, the figure-8 is great for two vocalists face-to-face or for tuning out off-axis sounds in a way that no cardioid can do. Most models use modern solid state FET electronics but some have been introduced that use vacuum tube amplifiers; some people like the sound of tube amplifiers, even though they are noisier and require transformer coupling.

Back to top

Miniature Electret Condenser Mics

The advent of miniature electret condenser microphone capsules has made the podium mounted wand/gooseneck style miniature head style microphone affordable for most applications.

All of the electret designs need either phantom or battery power. Most of the electret models come in either of two mounting configurations. The most popular has a XLR type connector at the bottom end, to be mounted in a common surface mounted female XLR connector. This type will operate on phantom power only. Other models have either a 5/8" female thread mount for mic stand mounts or a flange to be screwed down to a mounting surface. These have a cable with either an XLR connector at the end or a connector-box which will take a battery or phantom power.

Back to top

Miniature Microphones

The idea of hanging a microphone over a choir or stage is nothing new; the availability of miniature microphones for unobtrusive sight lines is new. Some models have a sort of wire device which can point the microphone in the right direction. All models are electret condenser mics which means that they must be powered by either phantom or battery power. Battery power is not convenient for most hanging-mic applications since the battery is hard to access from a ceiling. Some models have a wallplate cable-end compatible with electrical boxes for permanent installation.

Back to top

Multiple Microphone Phasing Problems

Whenever you use more than one microphone to record a source, there is a chance that certain frequencies will be out of phase. This means that a frequency may arrive at one microphone slightly before it reaches the other, and the two recordings will cancel each other out. This will sound odd when you listen back to the recording - certain notes will be louder than others, or the bass will be very loud or very soft. It is easy to run into phasing problems when miking in stereo, and using three or more microphones makes this problem even worse.

There are a few steps you can take to reduce phasing problems when recording:


The 3:1 Rule.
This rule simply states that a microphone should be three times farther from another microphone than it is from the source. So if you place a pair of microphones 6 inches away from an acoustic guitar, these mics should be 18 inches away from each other to minimize phasing problems.
Don't use more microphones than necessary.
The more mics you add, the better the chances for phasing to occur. It's often tempting to use a dozen tracks or more to record a drum kit when you have that many tracks available, but you may need to move the mics around for hours if phasing problems pop up. Of course, a stereo pair doesn't always do the trick, so you need to find the right compromise.
Watch out for reflective surfaces.
You might get phasing problems if the sound is bouncing off of a nearby wall or a music stand. Moving the performer or adding absorption to the problem area can often eliminate the problem. Often draping a towel over a music stand can eliminate high-frequency phasing problems from sound bouncing into the mics. Also remember that a cardioid mic pointed away from another performer may still pick their sound up as the sound bounces off of the back wall and into the mic.
Make sure that the microphones are in phase.
If one of the microphones is out of phase (two of the leads of the microphone cable are reversed or the phase switch is pressed on the microphone preamp) and the pickup patterns of the two mics overlap, there may be phase cancellation in distance-related frequencies.
Separate the performers.
If possible, make sure that the performers are as far apart from each other as possible to eliminate leakage between the microphones. In a larger studio, consider putting performers in isolation booths, or at least putting gobos between them. However, some gobos may themselves cause phasing problems from imperfect sound absorption or from covering the back of the microphone, thereby altering the mic's polar pattern.
Use a baffle.
Often an acoustic baffle can stop sound from leaking from one microphone to the next. You can place a baffle between two performers, or even between two microphones to increase separation. Try using a small baffle between the snare and high hat mics on a drum kit, for example, or between two mics on a piano.
Move the Microphone.
This is the easiest and most effective trick to get rid of phasing problems. Just get into the studio with headphones on and move the mics around until it sounds right!

Back to top

Microphone Placement

The placement of microphones is not an easy subject to write about. It is both an art and a science. Even the finest recording engineers in the world, who have dedicated their lives to recording, will tell you that they continue to learn new tricks and try new techniques when placing microphones.

The purpose of this chapter is merely to explain some standard practices in recording. These are typical reference points, but there is always room for experimentation. If these placements don't work at first, don't be afraid to move the mic several times until you get the sound you want. It is always better to get the sound right on tape in the first place rather than letting something slide and "fix it in the mix".

That said, let's dive into the controversial subject of microphone placement.

Vocals

Vocalists are among the most challenging sources to record, because there is such a wide dynamic range to a good vocal performance and a small difference in mic placement can have a huge effect on the sound.

Typically, the microphone is set up at the same height as the singer's mouth (standing up), about 12 to 18 inches away. You can try moving the microphone higher for a breathier or more nasal sound, or move it lower for a more resonant sound from their chest. Make sure that the microphone isn't too high - where the singer needs to stretch their neck or look up to the microphone - as this can put a strain on their voice.

You can also try moving the microphone closer for a more intimate sound, which captures every breath and mouth pop, or to take advantage of the proximity effect for more bass (see page 16). You can also try moving the microphone away to capture the ambience of the room or for a more natural sound.

Many recording engineers use a pop filter when recording vocals. This can help reduce very loud "p" or 'b" sounds that result from plosive breath noises from the vocalist's lips. (You can also try moving the microphone up or down to eliminate this problem, although this may change the sound.) Pop filters are also useful for showing a vocalist where to stand. Where a singer may slowly creep closer to a microphone during a session, the pop filter shows them how far away they need to be.

You might also need to change the microphone position for excessive sibilance, or very loud "s" sounds. Typically moving the microphone lower or farther away can help, but in extreme cases you might need to use a de-esser (a specialised compressor designed to reduce sibilance).

Watch out for reflections from a music stand. This can make the vocal recording sound metallic or ringy. Try putting a towel on the stand if this is a problem.

For background vocals, try positioning all of the singers in a semicircle around the mic. Move singers forward or back, if necessary, to adjust the balance between them.

Many recordists use a little compression while recording, but be careful not to use too much. A few dB of compression can help compress the peaks as they go to tape, but 15dB or more can squash the vocal and ruin the recording. It's much better to ride the mic preamp gain while recording than to rely on compression. (When you see the singer take a deep breath, turn down the level!)

Overall, try to record the most natural sounding vocal that you can. People are more accustomed to hearing someone sing than hearing any other instrument, so when something is wrong the listener will notice. Try listening to the singer in the studio room, then adjust to make the recording as accurate as possible.

Acoustic Guitar

There are several popular microphone placements for acoustic guitar. If you need to record in mono, you can pick one of them, or for stereo you can pick two or more and pan them left and right (or front to back, if you're a savvy surround mixer...).

  1. Bridge This area, where the strings make contact with the body of the guitar, has a very warm sound when miked correctly. Try placing the microphone 9 to 12 inches away, facing the bridge, tilted away from the sound hole, or from underneath pointing up. One problem with this mic placement is that the guitarist's hand may get in the way of the mic (or vice-versa). You might notice the sound changing as the player moves his or her hand up and down while strumming. This can be a difficult mic placement, but is well worth it when you find the sweet spot.
  2. Neck, at the joint The area where the body joins with the neck of the guitar has a natural, balanced sound. You can pick up the characteristic finger squeaks and slides while getting a balanced sound from the body. This seems to be the most popular placement for miking a guitar. A stereo pair with one microphone here and another at the bridge, being careful that both are the same distance from the guitar, can give a dramatically wide sound.
  3. Tuning Pegs Believe it or not, if you mike the "nut" right near the tuning pegs, you can pick up a very "jangly" sound. This area is often miked in addition to the bridge, then panned hard left and right for a dramatically stereo sound.
  4. Audience perspective For classical solo guitar, place a mic about three feet in front of the performer, level with the sound hole. This placement gives you a natural sound, a little darker than close-miking, and includes the ambience of the room. Mike in stereo (using one of the techniques described later) and move the mics even farther away for a more ambient sound.

Make sure the guitar player doesn't move around too much once you've found the magic spot. Try using a hard mount to keep the placement set, unless the performer taps his or her foot or hits the mic stand.

Electric Guitar

Place the mic in front of one of the speaker cones in the amp, about 4 to 6 inches away from the speaker. Putting the microphone closer will produce a bassier sound due to the proximity effect (see page 16). Some engineers will put the mic so close that the grill cloth is slightly pressed in.

Miking the edge of the speaker gives you a more mellow tone than the center - the closer to the middle of the speaker, the more edgy the sound gets. Try moving the microphone around while wearing headphones until the hiss is the quietest, this often gets the best sound from the amp.

You can also try moving the microphone back for a more natural sound. You can even try miking the cabinet in stereo to capture ambience. One popular technique is to use a low-cost dynamic microphone (such as a Shure SM-57tm) close on the speaker and the GT condenser mic further back, panned in stereo.

Grand Piano

The best way to get a great piano sound is to start with a great piano in a great room. Of course, a great mic technique doesn't hurt. Because of the wide dispersion characteristics of a grand piano, 2-microphone stereo techniques are almost always used. Below are three variations on miking a grand piano:

Pop/Rock Place the microphones over the hammers, about 6 inches away, face down. They should be spaced apart so that each covers a range of the piano, without being so close that they focus on one group of notes. You may also need to angle the mics away from each other to increase separation. You can also try moving the microphone on the lower range of the piano away from the keyboard, halfway down the harp towards the back of the piano, for a larger, warmer sound. This mic technique was popular in the 1980s for yielding a very percussive, rock and roll sound with a wide stereo spread.

Modern Jazz/Rock Ballad Place the mics in a 45 degree angle, one facing the keyboard and one facing the other end of the piano. The microphones can be from 6" to 3' apart, but if you spread them out you should decrease the angle. The mics should be about halfway between the strings and the lid (the lid should be all the way up), 6-12 inches inside the harp. This should give a very clear, yet warm sound.

Classical Set the microphones around four to eight feet away from the piano. Try a few different heights, in a nice-sounding hall you may want to go 10' high or more. Set the mics to Omnidirectional (on the AM52 and 62, not available on the AM51 and 61) to capture the sound of the room. (Note: When recording with spaced omnis, your recording may be out of phase unless panned hard left and right.) By moving the microphones farther apart, you can get a larger sounding piano, a closer microphone spacing yields a more intimate sound. If the room doesn't sound so great, move the microphones in closer and add digital reverb later.

Make sure you check the recording in mono or use a phase meter (if available) when recording a piano in stereo. It is very easy to get the mics out of phase, even if it's just in one range of the piano, especially in Omni mode. If phasing becomes a problem, move the microphones and trying again.

Drums

Rock and Jazz drum kits are often recorded with several microphones, then processed and mixed later:

  1. Kick Drum The Kick drum microphone is usually placed close to the front batter head, or inside the drum if the front batter head is removed. A closer mic position will give you a tighter sound, moving it back will make the kick sound bigger and deeper. In some cases it may be necessary to move the mic or turn on the -10 dB pad if the levels are clipping the mic preamp or the microphone's internal electronics.

    Snare Drum Snare drums aren't typically miked with a large-diaphragm condenser microphone, but you may want to try it when using brushes. A more common application would to be to use a low-cost dynamic microphone (such as a Shure SM-57tm) near the rim, facing the head. You might try adding a condenser mic (like the AM Series) on the bottom of the snare drum to capture the snap of the snares. You may need to reverse the phase on this mic.

  2. Overheads Place a pair of AM Series microphones on tall mic stands and place them about 2-5 feet above the kit. They should be roughly four feet apart, facing down over the cymbals. Move the microphones closer for less ambience.

    High Hat Place the microphone at the edge of the high hat, facing down. Miking the very edge of the high hat will produce an edgy sound with lots of the stick, moving the mic more towards the center will give you more of the bell sound of the cymbal. This is typically a small-condenser mic application, but the AM Series mics often work well here.

  3. Toms Toms can be close miked for a more present sound. Having the toms individually miked allows you to pan them from left to right and process them independently. You may need to use the pad. Make sure the drummer doesn't hit the mic with a stick!
  4. Room Mics If you're recording in a large, reflective room, try placing a pair of microphones in the room for a big, classic rock sound. A pair of AM52s or AM62s set to an Omni pattern work great for this. Try compressing these mics for an even bigger sound.

Back to top

Stereo Microphone Placement Techniques

There are several methods for recording a source in stereo. Some instruments, like our acoustic guitar example, can have specific areas close miked and panned left and right for an artificially wide stereo sound. However, if your goal is to accurately capture a performance in stereo, we have listed a few techniques which are sure to provide a great sound. Most of these techniques were designed for recording symphony orchestras, but work well for small ensembles and solo instruments as well.

X/Y

To set up an X/Y microphone (or coincident) pair, first set one microphone facing the left side of the source. Put the other microphone on a stand upside-down directly over the other microphone, so that the two are almost touching. Angle this microphone from 90 to 110 degrees away from the other one, facing the right side of the source. Set the patterns to Cardioid, or super-cardioid if you're using the AM62. The microphones can be as close or far from the source as you want, moving them further away will decrease the stereo separation and increase the room sound in the mics. This technique will give you a good stereo image with little reverberant signal, but stereo separation is not as good as some of the other techniques listed below.

Spaced Omni (AM52/62 only)

This is a popular technique for recording an orchestra. Set up the microphones four to eight feet away from the source. They should be set on stands level with the performer, but for more ambience you might try setting the microphones 10 or more feet in the air. The polar pattern should be set to Omnidirectional. This microphone technique picks up a nice depth and great image, but the center of the image may sound slightly softer or unfocused. Watch for phasing problems when using this technique, see the next section for more information.

Blumlein (AM52/62 only)

The Blumlein microphone technique uses two microphones in figure-8 patterns oriented 90 degrees from each other. The left facing microphone faces the left side of the source instrument (or ensemble) and the other mic faces the right side. At the point where these two polar patterns overlap, their sensitivities are down -3dB. Therefore, signals in the center are recorded equally by both microphones, and are appropriately balanced when played back on stereo monitors. This technique can yield an excellent stereo image and depth, while the rear lobes of the figure-8 patterns capture the ambience of the room.

ORTF

This microphone technique is designed to emulate the way your ears are placed in your head. A pair of cardioid microphones are placed facing away from each other at a 110 degree angle with their capsules 17 centimeters (6 3/4 inches) apart. At the point where their patterns overlap, the sensitivity is down -3dB, like the Blumlein system. This technique can produce the wide image and depth of the Blumlein microphone system with less reverberant signal.

Mid/Side

This system uses a pair of microphones to capture a very precise stereo image, but must be decoded or played back in a special way. The microphones are set up with one (the "mid") set to cardioid facing forward, and a second (the "side") set to figure-8 and facing 90 degrees to the left. The cardioid covers the majority of the sound, while the figure-8 microphone only records the extreme left and right sides. When playing back this system, the Mid microphone should be panned center, and the side mic should be bussed to two mixer channels - one panned left, the other panned right and out of phase. The Width of the recording can be controlled by changing the balance between the mid and side channels. The benefits of this system are an exact stereo image (when balanced correctly) and an accurate center channel recording, useful for mono-compatible broadcasting and left/center/right surround mixing.

Decca Tree

This technique was developed by Decca Records in the mid-1950s, and is still used on many Hollywood film score recordings. Three microphones (typically cardioid, but sometimes omni) are placed on stands ten to twelve feet above and slightly behind the conductor's head. The three mics are tilted approximately 30 degrees downward towards the orchestra, and angled from each other to cover the entire symphony (one aimed at the center, and the other two aimed 458 out from the center). In addition, two other microphones are typically placed on the edges of the orchestra, usually further back in the room to capture the ambience of the hall. This technique yields a realistic stereo image, provides a good balance between miking the entire orchestra and spot miking individual sections, and produces a discrete center channel which is useful for mixing in surround.

Back to top

Small Instrument Microphones

Technology originally intended for micro-miniature hearing-aid microphones has led to ultra small instrument microphones that can be attached to the instrument instead of a stand. Although such small diaphragms can not exhibit the lower noise specs of larger diaphragms, the close proximity that they are used in negates any such disadvantage. Many performers like to move around as they play, micro microphones that travel with the instrument removes a constraining influence from the performer. When dealing with percussion instruments such as drums, micro microphones can be placed in areas that no traditional microphone would fit out of the way of sticks.

Back to top

Stereo Microphones

Stereo microphones have traditionally been used for music recording, although the recording of sound effects and stereo video ambience has renewed manufacturers' interest in new designs. The stereo microphone is really two microphones in one common housing for convenient mounting, hanging, hand-holding or camera mounting. Some of the designs allow the separation of the stereo panorama to be adjusted by either mechanical or electronic means, the MS method can allow the degrees of separation to be adjusted remotely. Most designs have the capsules spaced close enough together so that the signal pickup point can be considered a mono compatible point-source.

Spaced-pair techniques require two separate microphones which can be mounted on a stereo bar or farther apart with two separate mounts. For those applications we recommend small diaphragm condenser microphones.

Back to top

Using a Windscreen or Pop Filter

Two common accessories used with condenser microphones are the windscreen and pop filter. These enhancements are designed to decrease the amount of air pressure which hits the capsule, which can sometimes cause a loud bass rumble or pop in the microphone's output.

A windscreen is designed to decrease bass rumble during outdoor recording. It is usually a large foam cover which slips over the top (diaphragm) portion of the microphone. There are other models, usually called "zeppelins" which look like a large blimp (sometimes covered with fur) and completely surround the mic. These are much more expensive than windscreens, but do an effective job of keeping wind noise out of the mic. While you should be able to find a traditional foam windscreen at your GT Electronics dealer, you will probably need to find a film location recording company to find a "zeppelin" model. Note: A windscreen may decrease high frequency response.

A pop filter is used to soften loud "p" or "b" sounds when recording vocals in the studio. A pop filter is usually made of nylon cloth stretched around a frame, usually threaded to screw onto a microphone stand. (A cheap pop filter can even be made from a pair of stockings and a coat hanger in an emergency.) This filter is placed in front of the diaphragm, between the microphone and the vocalist's mouth.

Back to top

Vocal Microphones

Why do most handheld vocal microphones look like ice-cream cones? (Sometimes called "Ball Mics"). The first of the modern vocal microphones appeared in the late 1960s. The popular Shure Unidyne (cardioid) had a tapered barrel which could easily slip in and out of a stand clamp, and fit nicely in a palm. The ball shaped windscreen reduced "P" popping when worked close. Most of the current designs follow this popular concept and look very similar, since the shape is very practical.

Proximity-Effect is the exaggerated bass produced when a cardioid microphone is used a short distance from the sound source. The only way to combat this effect is to reduce the bass response of the microphone to compensate. This reduction provides a mic frequency balance when working close to the mic, but if the mic is used at a greater distance than it was designed for it may sound harsh since it will not have enough bass response. A few vocal mics have a bass cut switch which can restore low end response so the mic can be used for instruments.

Many vocal microphones have a presence peak, which is a high frequency peak between 8000Hz and 10000Hz. This boost adds clarity and articulation to most voices and can compensate for poor sound system performance. Most of the higher priced dynamic and condenser vocal microphones have a less dramatic or no high frequency peak since they were intended to be used with higher quality sound systems.

Most vocal microphones are cardioid, which means that they have minimum pickup at the rear. Hypercardioid and Supercardioid mics have even less sensitivity at the sides, but do have a small pickup lump at the rear which the cardioids do not have, so are more critical in placement in regard to floor monitors.

Benefits gained as price increases are reduced handling noise, smoother response off-axis which reduces feedback problems, and more consistent response from one mic to the next.

Most vocal microphones are dynamic with traditional alnico magnets, some feature the new neodymium magnets which increase output level, reduce suspended mass and which allow better acoustic designs. Condenser elements are used in some models, they have lower distortion and better transient response, but do need either battery or phantom power.

Nearly all models include a stand clip in the price. Useful options include foam windscreens which can further reduce "P" popping, shockmount stand clips and spare strand clips since they are subject to the most abuse.

Back to top

Wireless Microphones

Wireless microphones are radio systems that replace the wire (or cable) used to connect a microphone to a sound system. A microphone cable is a simple device that is very reliable, low in cost, but restricts movement and can not be concealed by an actor.

Wireless microphones should only be used when a wired microphone is impractical. All wireless mics have two parts, a transmitter and a receiver. The transmitter is either an all in one handheld microphone with the radio transmitter in the handle or a belt-pack transmitter to which a lapel or head-worn microphone can be attached. The receiver represents the other end of the link and turns the radio waves back into an electrical signal and is plugged in to the same place a standard mic cable would go.

All transmitters use a battery to provide power and can be operated up to 10 hours before replacement is required. We recommend an alkaline battery which should be discarded after each use, you do not want failure in the middle of a show, don't be cheap.

Both AC and battery powered receivers are available. The battery powered models are for use in the field or on camcorders, use the AC powered models whenever possible, they cost less and work better. Better receivers have a feature called diversity reception in which two antennas are used to reduce signal drop-outs.

Most wireless mics use FM modulation and all must be on a frequency not used for other purposes. When more than one wireless systems is being used, each system must be on a different frequency. Two transmitters on the same frequency can not be used on one receiver. Some wireless systems are tunable (frequency can be changed) some are fixed frequency.

Tunable wireless systems need little planning when ordering since they can be tuned by the user. When ordering a fixed frequency system please have a frequency list of any other wireless mics or 2-way radios used in the vicinity, also a list of what channels local TV stations are on. We will be glad to help find compatible frequencies.

The reliable range of most systems is 50 to 100 feet. The enemy of quiet and reliable reception is interference from other radio systems and the distance between the transmitter a receiver. The closer they are, the stronger the signal is at the receiver; a stronger signal is a good thing.

The cost of wireless systems reflects the quality of the sound, immunity from interference, tunability and reliability. Wireless systems can never equal the sound of a simple microphone cable, but the higher the cost, the closer it gets.

Back to top

Wireless Microphones

There are a few categories of sound equipment where the axiom of "you get what you pay for" is as true as with wireless microphones. The idea of eliminating a microphone cable to enhance mobility is enticing yet fraught with pitfalls.

All wireless microphones have two distinct parts, the transmitter and the receiver. These replace a cable. A cable is very simple; it has two connectors and some wires in between. Not much can go wrong with it and if it does break, it is simple to fix or even simpler to replace. A wireless system involves a radio transmitter and receiver. The transmitter takes the microphone's signal and modulates it into a radio signal. This signal passes through the air to the radio receiver which demodulates the signal and delivers that signal to the mixer as though there was a cable present. Considering the hundreds of electrical parts involved in the process of eliminating a simple 3 part cable, it is amazing that wireless microphones work at all. Twenty years ago, wireless microphones did not work all that well or often. They are cheaper and much more reliable now.

Getting the best value for your dollar is what our salespeople can help you with. Wireless systems start at around $200.00 and go up to $5,000.00. What do you get when you spend more?

DIVERSITY:
Better receivers have two antennas and internal circuitry which takes the best of the two signals for more reliable reception.
REJECTION:
The ability to reject radio transmissions on adjacent frequencies is a trick which never comes cheaply. Users in big cities and other areas congested with radio traffic need higher priced receivers.
LARGE SYSTEMS:
In situations where more than 4 wireless systems are to be used at a time, cheaper systems may be prone to interfere with each other. Less expensive systems are available in a smaller variety of frequencies.
TUNING:
Some models allow changing the frequency of either the transmitter or receiver. This is a great feature for those on the road, rental systems or institutions who need to mix and match equipment for different uses and avoid changing interference conditions.
STABILITY:
Long term stability, when transmitters or receivers age they can drift in alignment, higher quality units are more stable over time.
GENERAL QUALITY:
Quality of construction and design lead to long term stability, higher sound quality, and reliability.
LARGE SYSTEMS:
In situations where more than 4 wireless systems are to be used at a time, cheaper systems may be prone to interfere with each other. Less expensive systems are available in a smaller variety of frequencies.

Back to top

Audio Technica Frequencies

Frequency Mfr. Code TV Channel Frequency Mfr. Code TV Channel
169.505 T2 TRAVEL 193.000 10C CH 10
170.245 T3 TRAVEL 194.400 10J CH 10
171.905 T4 TRAVEL 196.800 10W CH 10
175.800 7G CH 7 199.800 11G CH 11
176.200 7I CH 7 202.200 11S CH 11
181.200 8D CH 8 207.000 12L CH 12
183.200 8M CH 8 208.200 12S CH 12
184.200 8S CH 8 208.600 12V CH 12
187.600 9F CH 9 210.800 13B CH 13
189.900 9Q CH 9 213.800 13Q CH 13

Back to top

Azden Frequencies

Frequency Mfr. Code TV Channel Series
169.445 F1 TRAVEL PRO
169.505 A1 TRAVEL PERFORMANCE
170.245 F2 TRAVEL PRO
171.045 A3 TRAVEL PERFORMANCE
171.045 F3 TRAVEL PRO
171.845 F4 TRAVEL PRO
171.905 A4 TRAVEL PERFORMANCE
175.400 B1 CH 7 PERFORMANCE
178.225 B2 CH 7 PERFORMANCE
179.200 B3 CH 7 PERFORMANCE
181.400 C1 CH 8 PERFORMANCE
184.025 C2 CH 8 PERFORMANCE
185.125 C3 CH 8 PERFORMANCE
187.800 D1 CH 9 PERFORMANCE
188.200 D2 CH 9 PERFORMANCE
190.600 D3 CH 9 PERFORMANCE
191.300 D4 CH 9 PERFORMANCE
194.400 E1 CH 10 PERFORMANCE
195.425 E2 CH 10 PERFORMANCE
196.800 E3 CH 10 PERFORMANCE
197.325 E4 CH 10 PERFORMANCE

Back to top

Samson Frequencies

Frequency Mfr. Code TV Channel
174.600 ch 0 CH 7
177.600 ch 1 CH 7
181.600 ch 2 CH 8
183.600 ch 3 CH 8
190.600 ch 5 CH 9
192.600 ch 6 CH 10
195.600 ch 7 CH 10
196.600 ch 8 CH 10
199.600 ch 9 CH 11
202.200 ch 10 CH 11
208.200 ch 11 CH 12
211.200 ch 12 CH 13
213.200 ch 13 CH 13

Back to top

Shure Wireless Frequencies

Frequency Mfr. Code TV Channel
169.445 V TRAVEL
169.505 AD TRAVEL
170.245 AC TRAVEL
170.305 AH TRAVEL
171.045 AC TRAVEL
171.105 AG TRAVEL
171.845 W TRAVEL
171.905 AA TRAVEL
174.500 AZ CH 7
176.200 CA CH 7
177.600 CC CH 7
180.400 CD CH 8
182.200 CE CH 8
183.600 CF CH 8
186.200 CG CH 9
186.600 CH CH 9
189.000 CJ CH 9
190.600 CK CH 9
192.200 CL CH 10
192.600 CM CH 10
195.000 CN CH 10
196.600 CP CH 10
200.300 CS CH 11
202.200 CQ CH 11
203.000 CR CH 11
206.000 CT CH 12
208.200 CV CH 12
209.000 CU CH 12

Back to top

Telex Frequencies

Frequency Mfr. Code TV Channel Series
171.905 065 TRAVEL Pro-Star
171.905 065 TRAVEL FMR
171.045 066 TRAVEL Pro-Star
171.045 066 TRAVEL FMR
170.245 067 TRAVEL FMR
169.505 068 TRAVEL Pro-Star
169.505 068 TRAVEL FMR
174.075 064 CH 7 Pro-Star
175.000 019 CH 7 Pro-Star
175.000 019 CH 7 FMR
177.800 021 CH 7 Pro-Star
177.800 021 CH 7 FMR
178.400 022 CH 7 Pro-Star
178.400 022 CH 7 FMR
183.000 025 CH 8 Pro-Star
183.000 025 CH 8 FMR
183.800 026 CH 8 Pro-Star
183.800 026 CH 8 FMR
184.400 027 CH 8 Pro-Star
184.400 027 CH 8 FMR
186.100 070 CH 9 FMR
190.400 032 CH 9 FMR
191.300 071 CH 9 FMR
192.100 072 CH 10 FMR
195.800 036 CH 10 FMR
197.000 073 CH 10 FMR
198.100 074 CH 11 FMR
201.800 041 CH 11 FMR
203.100 075 CH 11 FMR
204.100 076 CH 12 FMR
208.400 047 CH 12 FMR
209.250 077 CH 12 FMR
210.100 078 CH 13 FMR
213.800 051 CH 13 FMR
215.300 079 CH 13 FMR

Frequencies for the FMR-150
TV Group Mfr Code Ch A Ch B Ch C
7-8 DBU1 178.075 179.350 181.575
7-8 BRN1 178.450 179.675 181.950
7-8 RED1 179.400 180.675 182.900
8-9 ORG1 185.375 186.650 188.875
9-10 YEL1 191.775 193.050 195.275
10-11 GRN1 197.000 198.275 200.500
11-12 BLU1 203.600 204.875 207.100
12-13 PUR1 208.450 209.725 211.950
13 TAN1 211.725 212.550 214.775
13 PNK1 212.475 213.750 215.975

More Telex Frequency Info

Back to top

Digital Recorders

Digital recorders have many advantages over conventional analog recorders. Since the analog input signal is converted into a stream of digital numbers, then back to analog, the signal is not subject to errors in frequency response or speed and gathers very little distortion even with multiple copies.

The input and output features of most digital recorders are similar, the major differences are in the recording medium including tape, magnetic and optical disk, and solid state memory (RAM).

Input and output features to look out for depend on your use. Line level analog connections for universal use with analog equipment, microphone level analog inputs for field recording and headphone outputs for field monitoring. If the recorder will be used for transferring signals in the digital domain there are both AES/EBU (XLR) and SPDIF (either RCA-Coaxial or Optical) connections. Some equipment has all of the above, some not, what do you need?

Since digital recording uses a very high quantity of data, some recording systems use compression to increase the recording time. This compression is usually not audible, but if the recording is to go through many generations of copying, a recording format that uses no compression might be desirable.

The use of the recorder determines which recording medium is the best choice.

Tape (DAT, ADAT, DTRS) offers the lowest cost removable media with the highest capacity. Best used for acquisition of field and studio recording, since cost is low and storage is easy. Simple editing such as rearranging the order of recordings through copying is no problem. Complex editing is difficult. Multitrack recording (ADAT and DTRS) can be mixed directly from the tape. Since the cost is low, most tape based recording systems do not to use any form of compression. The down side of tape recording is that the recorders use rotating heads like video machines, this makes them sensitive to dirt, shock, humidity and temperature. The heads also wear out over time.

Disk based systems have the advantage of random accessibility to any portion of the disk without having to wait for tape to wind. This is a great advantage when editing, complex editing is fast and easy, things can be moved around on the disk with ease. Magnetic hard-disk systems are the fastest but most are not removable from the recorder, limiting use to one project at a time. Non-removable systems make long term storage impractical. Removable hard-disk systems make it possible to work on multiple projects but the cost (hundreds of dollars per hour of recording) makes it an impractical medium for long term storage. Some people make the original recording on tape then transfer disk for editing, or record on hard disk and transfer to tape for storage. Transferring is time consuming.

Another method of disk recording is the optical disk. The optical disk is slower than the hard-disk and often lower in capacity, but is easily removable and cost is moderate. A popular miniature optical disk is called the MD (MiniDisk) and uses compression to record up to 74 minutes in stereo. Nothing touches the optical disk and there is no wear, it is much less sensitive to shock and temperature then tape.

Standard Compact-Disks are not recordable. There are both Recordable CD's (CD-R) which can be recorded on once, at a very low cost and rewritable disks (CD-RW) which are much more expensive and can only be played back in special recorders. Recordable CD's are good for distributing smaller quantities of CD's, not for master recording since they can not be erased. Look for them in the 'CD' section of our catalog.

The last method is the most expensive. It is possible to record directly into computer memory called RAM. For this purpose removable credit-card sized flash-RAM cards are available. This is useful in portable field recording and announcement players for building automation. RAM has no moving parts; there is not much that can go wrong with it.

Back to top

Reinforcement Speakers

Few things are as difficult to specify as speakers and microphones. Both are hard to test in a retail environment. Understanding how they are to be used is critical information. Must they be portable or permanently mounted? What sized room will they be used in and how many people will be in the audience? Will the speakers be used for sound reinforcement or playback? What sort of sound will be sent to them? Music? Speech? Foreground? Background? Are there esthetic or practical limits to size or weight? How loud must the system be? How much power is available to drive them with? What is the size for your budget?

Knowing most of the above, it is possible to specify the right speaker for the job and the most cost effective, considering your budget.

Background Speakers Are primarily for music playback at a low volume level and for occasional voice announce situations, usually built-in to the ceiling or flush mounted to walls.

Foreground Speakers Are larger and designed for situations where they are a primary focus of the audience's attention.

Reinforcement Speakers Are used to amplify the sound presented to live microphones which are usually in the same room and prone to feedback. The speakers must be placed in such a position as to minimize both direct radiation to the microphones and room reflections which can also cause feedback and reduce clarity.

Pattern Is the word used to describe the shape of the sound radiating from the front of the speaker. A wide room may require a wide pattern, a long narrow room may require a narrow pattern speaker.

Range Describes the frequency response of the speaker. A speaker used primarily for voice reinforcement need not reproduce deep bass frequencies, thus saving on size and cost. A musical group with no bass instruments need not carry overly large speakers either.

Power Describes the speakers ability to absorb different amounts of power from an amplifier over a period of time. The more efficient a speaker is, the less power it needs to operate. Generally it is better for the amplifier to be larger than the speaker's power rating.

Impedance Is the rating in ohms of how a speaker places it's load on an amplifier. The lower the number in ohms, the greater the load. When connecting multiple speakers to a single amplifier channel the total load must not pass below the amplifier's capability to drive a low impedance load. Most amplifiers will drive either an 8 ohm or a 4 ohm load, but few will drive a 2 ohm load. One 8 ohm speaker delivers an 8 ohm load. Two 8 ohm speakers in parallel deliver a 4 ohm load. Four 8 ohm speakers in parallel deliver a 2 ohm load to the amplifier. Only use the same model speaker when connecting multiple units in parallel.

Construction Most portable speakers are either made of plywood or molded plastic for durability. Portable speakers often have corner bumpers and handles, some have carpeted finishes, most have a protective grill over the speaker elements. Permanent mounted speakers are either designed to be mounted flush with a wall or ceiling surface, or be mounted or hung from those surfaces. Permanent speaker cabinets are usually either made from wood particle board, molded plastic or metal as in the case of smaller ceiling speakers.

Environment Most speakers are designed to be used indoors. Some are designed for outdoor use, most outdoor speakers are made of plastic or metal and are protected from humidity.

Termination Portable speakers are designed for rapid set-up and tear-down, they usually have 1/4" female connectors, some now have a more rugged Speakon connector which can have 4 or 8 terminals, useful for bi-amping. Permanent speakers usually have screw terminals for reliable long term connection, some ceiling speakers have solder or presson terminals.

Mounting It is best for all speakers to be placed high enough to be in the line of sight of all of the audience. Portable speakers may be places on a scaffold, placed on a shelf or mounted on a stand. Many portable speakers have bottom sockets for stand mounting, others may be adapted for that purpose. Permanent speakers must have secure mounts for the safety of the audience. Gravity can be a friend or enemy. A 10 to 1 ration of weight capacity is recommended for all permanent mounting systems. We also recommend that wooden cabinets be supported from the bottom to avoid stress on glued joints.

70 Volt Systems When speakers are a distance from the amplifier or many speakers are to be powered by one amplifier, a 70 VOLT System is recommended. "70 Volt" is a misnomer; it is really a high impedance distribution system. Each speaker has a transformer on it which can tap different amounts of power form the distribution system. The amplifier usually has a step-up transformer at its output. Having a high impedance distribution line allows smaller gauge wire to be used and many speakers to be connected to a single amplifier. Most background music and paging systems are "70 Volt".

Back to top

Headphones

Headphones are used not only for private entertainment, but also for professional monitoring. The most common uses and for field recording where a loudspeakers would be impractical or for musicians in the studio who need to hear each other or previously recorded tracks for overdubbing.

Four types of headphones are common.

The first is the Enclosed (Closed, Closed Back or Isolating) type. The enclosed headphone seals outside sound out and inside sound in. It is best used in noisy environments, as it has difficulty consistently reproducing bass frequencies since the seal against the head varies with pressure, hair and eyeglasses.

The second is called Open (Open-Aire, Open Back, Vented) type. The Open headphone is usually more accurate, consistent and lower in cost for the same performance as an Enclosed headphone. Comfort is usually higher since less pressure is required against the ear. Musicians often prefer them when playing or singing since they can hear some natural sound through them.

The third type could use either Open or Enclosed but is designed for voice communications, intercom, or language lab use. The frequency response is tailored for clear voice reproduction and not for music.

The forth is in-ear earphones. Used when talent is either on-camera or performing and does not want the phone visible. These either have the transducer at the ear like a hearing aid or clipped behind the neck with a clear plastic tube and earmold in the ear canal. In a pinch, consumer 'earbuds' may be used in this application.

Factors to consider when buying headphones. The higher the price, the wider the frequency response and the closer the two sides will match each other. The effect of headphones is to exaggerate frequency response and stereo width, making them hard to use for critical esthetic judgements. Chances are the more boring a pair of headphones sounds, the more they will sound like speakers. Watch out for impedance and power handling, most modern mixers and recorders require headphones to have between 30 and 90 ohms impedance, a higher impedance will work, but at reduced volume. Headphone amplifiers are a good idea since most built-in headphone amplifiers are quite low in quality.

Back to top

Power Amplifiers

Power amplifiers find uses in both studios and sound reinforcement, although the same amplifiers can be used in both environments, some models are more suited for each. When evaluating the power of an amplifier, it is important to note the power rating versus the impedance of the loudspeaker to be used. The peak power of the amplifier should be higher than the peak capability of the speaker, since speakers are more likely to be damaged by too small an amplifier. It seems that you can not get too big an amplifier for any application other than size and cost limitations. A bigger amplifier seems to do a better job of controlling the loudspeaker even at low volumes. Most modern professional amplifiers have good protection against short circuits and bad loads.

Back to top

Studio Amplifiers

Most modern amplifiers have good enough sonic characteristics to use for critical monitoring. The needs in the studio are special in that a quiet background environment is important. Many modern amplifiers use fans for cooling, and if the amplifier is to be mounted in the control room it must be quiet, if the amplifiers are to be mounted elsewhere such as in a closet this might not be an issue. Amplifiers without fans are called passive, or convection cooled, they often cost more than fan cooled models since they need much larger heat-sinks. Some designs may not have front mounted level controls, most professional models will have balanced inputs to reduce ground loop induced hum. Most monitor speakers have impedances between 8 and 4 ohms, so the ability to drive 2 ohms is not important.

Consumer HI-FI amplifiers are sometimes used in studios, other than their more fragile designs and lack of balanced inputs, they can do a good job when cost is a limitation.

Full Compass represents a full line of professional and consumer amplifiers for every application, call for advice on your next project.

Back to top

Equalizers, Crossovers, Filters

The terms equalizer comes from the telephone company, tape recorders and phonograph players, but is used today to mean other things. Telephone lines do not have flat frequency response, neither do tape recorders or phonograph players, they all need a type of tone or frequency response control to make their frequency response as "EQUAL" to flat as possible, so the term equalizer was coined to describe the circuit used to correct their response. Such equalizers are a built-in part of the systems described above.

The equalizers that we use in studios and sound reinforcement are different in that they are generic in purpose and often not used to "EQUALize" but to change that sound's frequency response from flat to something else. In Hi-Fi equipment the word for equalizer is "Tone Control" and may be a more accurate description for the common use of equalizers.

The Graphic Equalizer has a series of vertical slide-type controls each representing a specific band of frequencies. The knobs on these controls are arranged in a row to "Graphically" represent the frequency response created by "drawing" the graph with the knobs. Most graphic equalizers have the bands divided into 1-Octave, 2/3-Octave or 1/3 octave bands. The number of knobs can vary between 9 and 31 per channel, depending on how many bands there are. Most models include an overall level control and an overload light since boosting some frequencies may overload the circuitry necessitating backing off the overall level control. Some models may include high or low cut filters allowing the extremes of the frequency spectrum to be reduced. On some designs the bandwidth of each control narrows as the control is advanced, on some (called Constant-Q) the bandwidth is the same at all positions of the control. Graphic equalizers were originally designed to "equalize" the sound of a room, to make a sound system flat, and are often still used for that purpose. In sound systems the graphic is also used to cut down those frequencies that are prone to feed-back, and alter the frequency response for purposes such as increasing articulation. The graphic can also be used to modify the overall sound of a particular instrument or voice in a desirable way, they are easy to use and their operation and effect is most obvious.

Back to top

Compressors, Dynamic Controllers, Expanders...

Compressors and limiters are often confused but are somewhat similar. Compressors change the overall dynamic range, such that a compressor with a ratio of 2:1 would modify a signal so that a change in volume of 2-dB at the input would only change by 1-dB at the output. Most compressors have a variable compression range of 2:1 to 20:1 and beyond. A limiter is designed to leave the dynamic range of the signal unmodified until it reaches a certain threshold above which the signal is compressed at a high ratio so that it gets no louder. Some models do both, compressing the signal up to a threshold after which it is limited. Some models have controls for attack and release, which determines how quickly the unit responds to the incoming signal. Some models have automatic attack and release controls that adjust themselves according to the character of the incoming signal.

Some of the types of signals that benefit the most from compression or limiting are: voice, bass guitar, and kick drum. People sing and speak in such a way that their natural dynamic range makes them either too loud or soft. Also, the way that people move around in front of a microphone can affect their volume. Bass instruments such as guitar and drums are hard for most sound systems to reproduce, and listening to a mix at moderate levels can make a bass instrument seem to disappear under the mix at times, a compressor or limiter can pull those instruments up and make them consistent.

Limiters and compressors can also be used on the overall mix, often to keep recorders, sound systems and transmitters from overloading on loud passages.

Expanders and Gates often confused but somewhat similar. Are the opposite of compressors and limiters. They work on similar principles, but can exaggerate the dynamic range of a signal rather than reduce it as compressors do. Gates turn the signal on and off.

Common uses include bringing as instrument up out of background noise or bleed caused by other instruments, reduction of background noise and special gated effects. Some gates can be "keyed" by other signals, making the volume of an instrument dependent on the volume of another.

Back to top

Effects, Reverbs, Enhancers

If you wonder why your recordings sound dull compared with most of the album and radio sounds you hear, you have not yet discovered the world of enhancers/exciters. First brought to the market on a rental basis by Aphex, these units are now available to everyone at reasonable prices by a number of manufacturers. What do they do? The literature rarely gets to the point, but here is our explanation.

Where compression and limiting can make signals audible that may not be loud enough, these devices seem to add "Air", "Crispness", "Intelligibility", in a way that conventional compressors and equalizers cannot. If we boost high frequencies with an equalizer, things may sound too thin or raspy. One of the things that all of these units do is to selectively boost high frequencies when it sounds OK to do so, and not boost them when the signal naturally has enough. Another thing that some units do is to add extra harmonics to the signal that were not there to begin with; this can make some signals sound "Richer".

The price of good digital reverb and effect units has come down just as the prices of good computers has plummeted. Most digital processors on the market today can do more and do it better than units costing ten times as much only five years ago. Not only will these units produce convincing reverberation simulations but also reverb and other effects that have no place in nature but tease our ears when we need the "new sound". Some models will produce up to 12 effects at a time. Some units are more oriented towards general studio effects, some are oriented to guitar and other instrument effects. Some models also include effects such as compression and equalization, in addition to the digital effects. Most models after a preset catalog of effects and variable control of parameters such as decay time, damping, gating etc, and preset memory of variable settings that can be recalled. MIDI remote control of preset selection and parameter setting is common.

Back to top

Digital Reverbs

The price of good digital reverb and effect units has come down just as the prices of good computers has plummeted. Most digital processors on the market today can do more and do it better than units costing ten times as much only five years ago. Not only will these units produce convincing reverberation simulations but also reverb and other effects that have no place in nature but tease our ears when we need that "new sound". Some models will produce up to 12 effects at a time. Some units are more oriented towards general studio effects, some are oriented to guitar and other instrument effects. Some models also include effects such as compression and equalization, in addition to the digital effects. Most models offer a preset catalog of effects and variable control of parameters such as decay time, damping, gating, etc., and preset memory of variable settings that can be recalled. MIDI remote control of preset selection and parameter setting is common.

Back to top

Digital Boxes

Many electric or electronic instruments are difficult to mic and can sometimes be better picked up by using a direct box. The direct box eliminates the microphone by connecting directly to the instrument and converting the instrument's unbalanced 1/4" output to a balanced XLR microphone level output that can be hooked directly to a mixer's microphone input. The bass guitar is very difficult to mic and reproduce and is best served by a direct box. Most keyboards and other electronic instruments also benefit from a direct box hookup. Electric guitar is usually best mic'd with a dynamic mic in front of the amp. Since the guitar amp and speaker have a lot to do with the total sound of the instrument, a direct box will not do it justice.

Direct boxes come in two flavors, active and passive. A passive direct box has an impedance and matching transformer as the internal element. An active direct box uses an electronic circuit to convert the signal and must be powered by either a battery or phantom power. Most direct boxes have dual 1/4" jacks so that the instrument input can be looped through to an amplifier for local monitoring. Some models have ground lift switches to help eliminate ground loops.

Back to top

Graphic Equalizers

The Graphic Equalizer has a series of vertical slide-type controls, each representing a specific band of frequencies. The knobs on these controls are arranged in a row to "graphically" represent the frequency response created by "drawing" the graph with the knobs. Most graphic equalizers have the bands divided into 1-Octave, 2/3-Octave or 1/3-Octave bands. The number of knobs can vary between 9 and 31 per channel, depending on how many bands there are. Most models include an overall level control and an overload light, since boosting some frequencies may overload the circuitry necessitating backing off the overall level control.

Some models may include high or low cut filters allowing the extremes of the frequency spectrum to be reduced. On some designs the bandwidth of each control narrows as the control is advanced, on some (called Constant-Q) the bandwidth is the same at all positions of the control.

Graphic equalizers were originally designed to "equalize" the sound of a room, to make a sound system flat, and are often still used for that purpose. In sound systems the graphic is also used to cut down those frequencies that are prone to feed-back, and to alter the frequency response for purposes such as increasing articulation. The graphic can also be used to modify the overall sound of a particular instrument or voice in a desirable way; they are easy to use and their operation and effect is most obvious.

Back to top

Pro Power Distribution

For over 20 years, ETA has been in the business of developing high amperage theatrical lighting systems. From that knowledge base evolved an extensive line of rack mounted professional power distribution products designed to protect delicate and sensitive electronic equipment. If your investment in equipment is significant to you, you need something better than a power strip. You need quality power distribution. This guide was designed to help you select the right AC power distribution for your requirements.

All ETA Power Distribution products protect against the potentially damaging spikes and surges that occur normally on AC power lines. Interference caused by radio frequency transmissions is filtered out. Hums and buzzes caused by other devices sharing an electrical circuit (Electro-Mechanical Interference) are routinely eliminated by all models of ETA power distribution. In addition, most ETA models are ETL or UL listed assuring product safety.

- Models with lights to illuminate your work environment. (ETA versions with lights feature easy to replace bulbs.) - Units designed specifically to accommodate multiple wall warts. - Units with Digital Volt Meters allowing accurate line voltage assessment before power is exposed to delicate gear. - Units with AC line regulators that will automatically adjust varying line voltage to a safe range. - Units that subdivide your equipment list into groups then sequence those circuits to avoid blowing breakers in the on-rush" mode.

How do you get your entire system plugged into one wall outlet? You need quality AC power distribution that takes the wall power and distributes that power to your many devices. Quality power distribution performs several functions before your equipment is exposed to the potentially problematic electricity from the wall.

AC power is by its nature, unpredictable. It can vary in the amount of power delivered to your equipment in short bursts called spikes and surges. These spikes and surges can cause damage to your equipment or at the very least, cause your equipment to perform erratically. THESE AC PROBLEMS CAN BE ELIMINATED WITH PROPER SPIKE AND SURGE PROTECTION. All ETA PD models provide the very best in spike and surge protection.

AC power can also vary in the amount of power delivered over a longer period of time. Most of your components do not perform properly outside of a range of line voltage from 100 volts to 125 volts. In many instances your line voltage may vary. It is always wise to know what the line volt age conditions are before you plug your valuable devices in. Having a precise line voltage monitor allows you to see how much voltage is coming from the wall prior to exposing your quipment to it. The ETA power distribution models with a "V" in the model number such as the PD11LV and the PD10VR include a digital voltmeter that allows you to see what the line voltage is. When you see that it is within safe limits, switch on the ETA PD and current is allowed to pass to your components. If you would like protection from longer term line voltage variances, (sagging line voltage can cause brown outs and limit performance/overabundant line voltage can potentially damage your gear) ETA has 2 models that regulate the amount of line voltage. Regardless of what is coming from the wall, the ETA PD10VR and PD10VRS models will always output 117 volts, the right amount, to your equipment.

Noise can be induced into your musical creations through your AC power lines. Electro-Mechanical Interference (EMI) occurs when another device on the same electrical circuit causes noise.A refrigerator, ice maker, or air conditioner are frequent offenders. Just when you can least afford it, a buzz o