[sdiy] Reverse sawtooth / Wavetables

[Paul Maddox]

Tom,

Quality of???

resolution? SNR?

am interested.

>
> Unfortunately, that was my experience. I tried using half-wave tables when I was designing my DWGS oscillator. This allowed me to get 1024-point waveform tables into the RAM available. In the end, I dropped the halfwave table, reducing the waveform size to 512 points, and used the space I gained from taking out the halfwave logic to do a linear interp between waveform points. The gain in quality from the linterp far outweighed the loss from halving the table size.
>
> Again, Hal Chamberlin has been there before me, and gives some figures on Pg 429 for table lookup noise:
>
> Sine waveform, no interp:
>        256 points:     42.99dB
>        512 points:     49.03dB
>        1024 points: 55.05dB
>
> Complex waveform, no interp:
>        256 points:     23.56dB
>        512 points:     29.55dB
>        1024 points: 35.41dB
>
> Sine waveform, linear interp:
>        256 points:     85.19dB
>        512 points:     97.23dB
>        1024 points: 109.28dB
>
> Complex waveform, linear interp:
>        256 points:     42.75dB
>        512 points:     54.76dB
>        1024 points: 66.82dB
>
> This shows a clear benefit from putting the linear interpolation in, even if it means kicking the halfwave tables out.
>
> T.
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