The DSLR-AGCY was developed to allow disabling of the Auto Gain Control in Canon and other similar HD DSLR cameras. This cable allows you to split your audio tracks. One end of the cable is used to stream a continuous tone from an iPod or other mp3 player to the camera. This fools the camera into lowering the audio gain. The other end of the cable is used to connect a microphone or preamp to the camera. Only one channel is recorded but that is easily resolved in post production by deleting the "tone" channel and duplicating your "good" channel. This provides a solution to the cameras' lack of manual audio controls.