This sketch demonstrates how it is possible to put two signals on one AudioOutput.
You do need to be aware that the AudioOuput will simply sum all of the signals that are attached to it. This means it is your responsibility to make sure the total signal doesn't clip. Clipping occurs when a sample value is greater than 1 or less than -1 and will happen if you have two signals whose amplitudes are both 1, for instance. If the signal exceeds the range [-1, 1] it will be limited by the system, so you won't get nasty sounding distortion but your signal will sound slightly different.

Use the knobs to adjust the frequency, amplitude and pan of the two signals. In particular, notice what happens when you put the frequencies very close together.

Source code: Polyphony

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