Use Bus.audio to allocate private buses safely, avoiding conflicts with hardware I/O buses

SuperCollider’s audio buses are numbered: 0 to numOutputBusChannels-1 are hardware outputs, next block are hardware inputs, the rest are private internal buses. Hard-coding an integer bus index (e.g., Out.ar(6, sig)) risks conflicts if hardware I/O counts change. Instead, use Bus.audio(s, numChannels) to allocate: SuperCollider automatically picks the lowest available private bus. A ‘multichannel bus’ in SuperCollider is just a block of adjacent single-channel buses; allocating a 2-channel bus reserves two consecutive indices. When you pass a Bus object as a Synth argument, it’s automatically converted to its integer index.

Examples

~reverbBus = Bus.audio(s, 2); // allocates 2 adjacent private buses y = Synth.new(\reverb, [\in, ~reverbBus]); x = Synth.new(\blip, [\out, ~reverbBus]);

Assessment

What is the difference between hard-coding bus index 16 and using Bus.audio(s, 1)? When would bus 16 be an unsafe choice?