Effort post ahoy!
[color=rgba(0, 0, 0, 0.701961)]I can’t say I’ve played with AM on the A4 a whole lot but I do have experience with what the MS-20 calls ring mod, and the behavior is similar if you set it up right so it’s a good starting point for experimentation. Here’s how:
[color=rgba(0, 0, 0, 0.701961)]First, go to the sound options page and turn off oscillator drift. We want a consistent baseline while we’re learning what the hell we’re doing.
[color=rgba(0, 0, 0, 0.701961)]Back to the osc settings:
[color=rgba(0, 0, 0, 0.701961)]OSC 1: Square wave, knobs at default, level at 0.
[color=rgba(0, 0, 0, 0.701961)]OSC 2: Square wave, knobs at default, turn it up.
[color=rgba(0, 0, 0, 0.701961)]AM1 off, AM2 on, TRG on.
[color=rgba(0, 0, 0, 0.701961)]Kill the filters.
[color=rgba(0, 0, 0, 0.701961)]Play a note (or better yet set a single infinite note in the sequencer) and what you’ll effectively hear isn’t too far removed from a pulse wave. (If you think you know AM, why might this be? Think of what’s going on with the waveform.)
[color=rgba(0, 0, 0, 0.701961)]Now, the key to ring modulation is that it’s real, real sensitive to detuning. After a few cents the detuning turns into an enharmonious clangor – that hard sound we associate with rings. Let’s experiment then with what happens as we detune Osc 1 (remember, Osc 1 is producing no sound but is modifying Osc 2). Slowly turn the FIN knob up just a bit and you’ll get a harder version of oscillator beating. After about +30 or so you’ll start getting that clangor. Keep going – you can keep turning the fine tune up and the TUN knob will also incrememnt when you’ve gone a full semitone. At a full semitone it’s just some weird mess, but keep going and you’ll find spots where it sounds relatively stable like a hard oscillator sync, such as at +5 and +7 semitones. By the time you’ve gone all the way to a full octave up it sounds like a pulse wave again, except thinner.
[color=rgba(0, 0, 0, 0.701961)]At this point you have a basic idea of what it does and how to control it – keep it around an octave or fifth for that sync-ish yet musical sound, farther away gets you less tonal stuff. Now try some experiments:
[color=rgba(0, 0, 0, 0.701961)]AM is sensitive to the modulating osc’s pulse width. Try different PW settings on Osc 1 and PWM. It sounds different when you go left than when you go right, although I don’t really know why.
[color=rgba(0, 0, 0, 0.701961)]Modulate the tuning of Osc 1 with envelope 2. Setting Osc 1 to a 'stable (octave or fifth) setting and the envelope sustain/release to 0 will get you a clangy transient at the start of a note.
[color=rgba(0, 0, 0, 0.701961)]And of course play with an LFO. Set the retrigger to TRG to lock the clangy parts to the rhythm. Try both positive and negative pitch mods for Osc 1. The Exponenial and Ramp LFO waveforms are especially fun here. My favorite is speed at -16, multiplier at 36x and an exponential waveform, with a depth around +12. Or the same settings with a square LFO for a dirty take on that 80s-esque synth pop bass.
[color=rgba(0, 0, 0, 0.701961)]Finally, when you’re done with that you can start trying out other waveforms. This is beyond what the MS-20 can do (it can only ring mod a pulse against a square) so I’m in uncharted territory here. Just remember to go slowly when experimenting, changing only one parameter at a time until you’re sure how it affects the sound. There’s a zillion ways you can tweak things even without getting the filters involved, and it’s easy to lose track of what each parameter is contributing.
[color=rgba(0, 0, 0, 0.701961)]Have fun!