Demux

Demux is a little utility I wrote to demultiplex soundfiles with arbitrarily large numbers of channels. It runs in a Terminal window, so it's good for Mac OS and Linux. (Experienced coders could probably figure out how to run it on Windows too.) You can download demux here. Demux was inspired by the 32 channel limit on the otherwise excellent DiskIn, a unit generator of SuperCollider.

Demux relies on the wonderful libsndfile by Erik de Castro Lopo.

Once libsndfile is installed on your machine, you can compile demux by typing the following invocation into a Terminal window, after navigating to the directory that contains "demux.c".

cc -o demux demux.c -lsndfile

Now you have an executable file called "demux". You can move it to wherever you store your binaries. Demux has three arguments: an input file (containing any number of channels), the intended output file (which will be mono) and the channel number to extract. To extract the 86th channel of a soundfile called "gorgon.aiff" type the following:

demux gorgon.aiff gorgon_ch86.aiff 85

Demux counts channels starting at 0, so 85 is actually the 86th channel. Be careful not to get your input and output names mixed up, or you might accidentally write over your original file! The extracted mono file will be in the same format (same sample rate, bit width, and file format) as the source file.

Once a multichannel file has been demultiplexed to mono files, DiskIn can stream all the channels off the disk, assigning one synth to each mono file. Et voila: streaming soundfile playback of an arbitrary number of channels in SuperCollider.

Technical note: My code makes the rash assumption that its ints will have at least 4 bytes apiece, and therefore be more than sufficient for reading 24 bit integer samples. If that's not the case on your machine, you may need to change the code to read long ints. Or if you're working with soundfiles stored as floats, you may wish to explore the floating point I/O available in libsndfile.

Demux is intended to serve as a stopgap until DiskIn or some other Ugen is written to stream multichannel soundfiles without hard-coded channel limits. For now, it solved my multichannel problem - maybe it can solve yours too!

Demux is dedicated to the superb CAF developed by Apple.

June 25, 2012.

p.s. A note of thanks to members of the SuperCollider community for quickly informing me of SuperCollider's current limits regarding multichannel soundfile playback. The conversation that motivated this code may be read here.