[sDIY](early) wavetable synthesis

[Paul Maddox]

MB,


>If you reproduce the wave on the basis of some other sampled wave, you
>are resampling a signal which already has been sampled, so its spectrum
>is not limited. Lots of aliasing typically occur in such cases (the cha-
>racteristical lo-fi sound of the Amiga/tracker music). Pro samplers
>usually apply interpolation to the waveform stored in the memory before
>the resampling process. Interpolation may be thought of as lowpass fil-
>tering whose aim is to limit the spectrum (to have more smooth waveform.)
>

Hmmm, My PPG VCO sounds fine, the only thing I have vagually described as a 
filter is a uA741 as the output opamp, it filters enough of the signal for 
me.. mine sounds fine.. :-)
anyway, 99% of the time, the output of most VCO's goes through a filter...

>
>Well, AFAIK it IS used. You must not skip samples from the wavetable, if
>the wave is not appropriately smoothed (i.e. its bandwidth is appropriately
>limited), otherwise heavy aliasing occurs.

yes, haveing spoken to wolfram franke and looked extensivly at the PPG 
stuff, as far as I can tell wavetable synths play ALL the samples in a wave 
(in the case of the wave 256 samples per cycle) at a higher frequency, 
simply skipping bits is just not on, and only make for a far far more 
complex circuit to do this than just a plain high speed osc, or even plain 
phase-accumulator oscilator.

>I understand it might be confusing without a deep knowledge on the
>Fourier transform properties. Try the excellent Bristow-Johnson tutor
>on wavetable synthesis from the music-dsp site.
>

Whats the URL for this music-dsp site?

Paul



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