The channelInterpretation property of the AudioNode interface represents an enumerated value describing how input channels are mapped to output channels when the number of inputs/outputs is different. For example, this setting defines how a mono input will be up-mixed to a stereo or 5.1 channel output, or how a quad channel input will be down-mixed to a stereo or mono output.
The property has two options: speakers and discrete. These are documented in Basic concepts behind Web Audio API > up-mixing and down-mixing.
The values are documented in Basic concepts behind Web Audio API > up-mixing and down-mixing.
In summary:
speakers-
Use set of "standard" mappings for combinations of common speaker input and outputs setups (mono, stereo, quad, 5.1). For example, with this setting a mono channel input will output to both channels of a stereo output.
discrete-
Input channels are mapped to output channels in order. If there are more inputs that outputs the additional inputs are dropped; if there are fewer than the unused outputs are silent.
const audioCtx = new AudioContext();
const oscillator = audioCtx.createOscillator();
const gainNode = audioCtx.createGain();
oscillator.connect(gainNode);
gainNode.connect(audioCtx.destination);
oscillator.channelInterpretation = "discrete";