Audio Channel Assignment

When using a multi-channel sound output card, you may want to assign certain audio file channels to specific sound outputs. This channel-to-output assignment is stored in the WAV file itself. By default, the first six channels are assigned to sensible outputs, as shown in the “Default Channel Assignment” illustration below. However, the remaining two channels are by default assigned to “Front Left of Center” and “Front Right of Center”, which doesn’t match what most multi-channel sound cards expect.


Default channel assignment in an eight channel sound file.

Many sound cards expect channel 7 and 8 to be assigned to the “Side Left” and “Side Right” channels. Some audio editing applications may allow you to assign the sound channels to the desired outputs as you save the file. Alternatively, you can use a tool such as the “WATCHOUT Sound Channel Shifter” (attached to this recipe) to easily modify this setting in the audio file. ChannelShifterAfter.png

Channel 7 and 8 re-mapped to the desired outputs.

To use this tool, drag the file onto the Channel Shifter, select the desired channel arrangement and click Save (or “Save a Copy…” if you prefer to keep the original file unchanged). A sample eight-channel sound file is also attached, for testing purposes.

Note that you can use this tool even on a regular mono or stereo file to assign its channels to the desired outputs – it doesn’t have to be a multi-channel file. Indeed, using a set of mono files, where each file is assigned to a particular output, may sometimes be an alternative to using a single multi-channel file, unless phase accurate playback is required across the channels.

To use the ChannelShifter.air application you need to have Adobe AIR installed on your computer. You can download it here:

Files attached to this recipe: