[sdiy] AS3397 what is it?

[Tom Wiltshire]

> What exactly do I need to supply? One waveform for fundamental pitch? And another waveform with some relationship to the first for waveshaping?

What you've got is basically a linear ramp integrator. There's one input for reset pulses to reset that integrator back to 0V. Those reset pulses will set the fundamental pitch. You also have a "Waveshape CV" which determines how fast the integrator charges. This is important because *it needs to match the reset pulse period*. The integrator output is fed to a waveshaper. From 0-2.5V the output rises. From 2.5V to 5V, the output falls. From 5V up, the output stays at 0V.
Like this, the Waveshaper CV can create different waveshapes. If the waveshaper CV is set at a low level, the integrator will ramp up towards 2.5V. If it's set perfectly, it will *just* arrive there as the reset pulse arrives, creating a perfect ramp waveform. If we now double the Waveshaper CV, the integrator will charge twice as fast, so it will arrive at 5V just as the reset pulse arrives. In this case, the waveshaper output will go up and then down again, so we have a triangle waveform. Note that if we change the frequency, we will have to change the waveshaper CV as well or the waveshape will alter (or ramp amplitude in some cases).

Other "clipped triangle" waveforms are possible by reducing the waveshaper CV from this point so that the wave doesn't get back down to zero before the reset pulse arrives. This would be like a triangle wave with a hard sync. There's also a standard comparator and pulse width CV for square and pulse waveforms, so you can make those too.

So what you need to supply is:

a) A series of brief reset pulses (the datsheet schematic shows a squarewave fed through a HPF for this).
b) A Waveshaper CV voltage for the frequency you're trying to generate to get the ramp/triangle to match the reset pulses.

HTH,
Tom