6581 phase-accumulating oscillators

From: Richard Atkinson (Richard.Atkinson_at_cl.cam.ac.uk)
Date: 2000-11-19 00:07:40

Has anyone ever used the SID's phase-accumulating oscillators together
with a fast frequency register routine to generate phase-modulated sounds?

I'm thinking about the possibilities of running a tight loop constantly
re-writing the high frequency register to add different values to the
phase-accumulating oscillators in triangle waveform mode to produce
arbitrary 11 bit waveforms.

The slew rate is limited by the maximum number you can add to the
oscillators every cycle, which produces 4kHz triangle waves. However, a
sinusoidal wave with that gradient at t=0 wouldn't be much lower, and
there are all sorts of other noises one can imagine.

This can all done even better on SuperCPU machines where you can write to
the sound chip every 1MHz bus cycle.


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