Analog mixer

ATMOSYNTH built-in module

Sums up to four inputs into one, each at its own level, through a summing stage that saturates: the mixer of a Moog monosynth, where the levels themselves are the drive. A Level of 1 is a source at its own height, and on its own it passes all but clean; turned past that, or with others beside it, the sum leans into a soft curve that rounds its peaks off, so a hot mix thickens, compresses and grows a gentle edge. Because every input goes through the one stage, turning one source up squashes the others under it, which is a good part of why two oscillators driven together sound like one instrument rather than two. A quiet mix is a plain sum: at small levels the curve is a straight line at a slope of one. There is no Drive knob, because one would only be every level turned up and Output level turned down. The curve leans to one side, the top of the wave rounded a little sooner than the bottom, so what it adds is not only the hollow odd harmonics a symmetrical curve makes but the even ones as well — the second, an octave above the note, which sits with it rather than against it. Leaning to one side also moves the middle of the sound while it is driven, and that drift is filtered away under 5 Hz, below any note, so silence in is silence out. The curve is worked out at four times the rate and filtered back down, so what a hard drive makes above what the rate can hold is not folded back under the note; that costs four milliseconds of delay. Driving it harder also makes it louder, which is what Output level is for. A Moog's mixer has a Feedback level as well, the filter's output brought back into the mix, and there is none here on purpose: a wire taken back round in a patch arrives a block of 128 samples late, so what it makes is a comb ringing at a few hundred hertz rather than a growl. Each channel's level and the output level are inputs as well as knobs, each with a depth of its own: an envelope into Level 2 fades that input in under the others as a note starts, driving the stage harder as it rises, and an LFO into Output level is a tremolo.