understanding some terms and theory (re wavetables)

[jorgen.bergfors at idg.se]

>errrmm, nope...
>what they do on top of this is interoplate (in real time it would seem) from >one waveform to the next so you only have two waves forms, a start and an end >on the eprom.

I thought the PPG worked like this:

You have a long wave in the PROM that changes ever so slightly for every cycle. It might start as a sawtooth and end up as a square. The cycle length is exactly 128 (or 256) bits long and the ROM contains maybe 128 or 256 cycles.  Now, by reading 128 (or 256) bits in a row, but changing the start point, you can smoothly (or abruptly depending on the waveform that modulates the startpoint) change the timbre to animate the sound.
With this method you don't need any interpolation or other fancy processing. Just increment (or decrement) the register that sets the start point. You also won't get any aliasing as the clock frequency is always harmonically related to the fundamental (128 or 256 times). You might need a fairly large PROM if you want many different wavetables, but today that shouldn't be a problem.

/Jorgen