Multichannel sound

In general, we deal with stereo sound, i.e. we use two speakers and pan between them. Sometimes it's nice to work with four or more speakers though, and enjoy that surround sound experience.

We set up for multichannel sound in a similar way to how we do separate audio outputs. With separate outputs we are probably sending multiple stereo outputs though, whereas with multichannel sound we generally send one output, but with multiple channels.

Here's an example supercollider startup file, for panning across four channels:

 (
   s.options.numBuffers = 1024 * 256;
   s.options.memSize = 8192 * 16;
   s.options.maxNodes = 1024 * 32;
   s.options.numOutputBusChannels = 4; // total number of channels output 
   s.options.numInputBusChannels = 2;
   
   s.waitForBoot {
       ~dirt = SuperDirt(4, s); // pan across four channels
       ~dirt.loadSoundFiles;
       ~dirt.start(57120, [0, 0, 0, 0, 0, 0]);
   };
   s.latency = 0.3;
 );

Have a look at SuperDirt's documentation for more details, in particular the example superdirt_startup.scd file.

This line sets the number of output channels coming from supercollider:

   s.options.numOutputBusChannels = 4; // total number of channels output 

This sets the number of channels to pan across. For multichannel sound, this will generally be the same number as above.

   ~dirt = SuperDirt(4, s); // pan across four channels

Each 0 in the below represents one orbit, giving us six orbits. You probably want to keep these as zeroes, so every orbit starts from the first channel.

   ~dirt.start(57120, [0, 0, 0, 0, 0, 0]);

That's it! You can save this code in your supercollider startup file (which you can find via the supercollider menus) so you don't have to run it manually when you start supercollider.

Then to use it, you can use things like:

d1 $ sound "bd*16" # pan saw

The above will play kick drums in a ring around all the speakers. If you had four speakers, by default they'd be in position 0, 0.25, 0.5 and 0.75. Therefore 0.125 would be halfway between the first two speakers, and 0.875 would be halfway between the first and last speakers. Once you get up to 1, you're back to the first speaker again.

Because 0 and 1 are the same speaker, the jux function doesn't work well (as it will play the original pattern in position 0, and the transformed pattern on pan position 1, which in multichannel sound, are the same speaker. Instead, you can use juxBy 0.5, or jux', which distributes a list of functions across a multichannel ring.

d1 $ juxBy 0.5 rev $ sound "bd cp sn:2 mt*2" # pan saw

d1 $ jux' [id, rev] $ sound "bd cp sn:2 mt*2" # pan saw

d1 $ jux' [id, rev, fast 2] $ sound "bd cp sn:2 mt*2" # pan saw