[sdiy] How to make wavetables? What size?

[Andre Majorel]

On 2005-05-20 10:48 +0100, Paul Maddox wrote:
> Andre,
> 
> >With a 256-frame wavetable, the spectral content is limited to
> >128 harmonics. At a fundamental frequency of 50 Hz (the low G on
> >a bass), the spectrum stops at 6.4 kHz.
> 
> really?
> there was me thinking a square wave had a load more harmonics.

Yes, you have a point but what can I say ? In practice, it doesn't
work for me.

I'm not good enough at math to work out the actual spectrum. But a
point to consider is that a square wave only has odd harmonics.
The first harmonic above the fundamental of 6.4 kHz square wave is
at 19.2 kHz. In between, there is absolutely nothing.

A 50 Hz sawtooth has 273 harmonics in the same frequency range
(6400 Hz, 6450 Hz, 6500 Hz ... 19950 Hz, 20000 Hz).

It's of course a lot more complex than that because a typical
wave table is not just a 128xf0 square wave but the math is beyond
my abilities.

> >Whether or not this is a big deal is up to you. When I tried
> >Paul's Miniwave (256-frame wavetable), I remember wondering "why
> >won't the LPF open fully?" and Paul telling me "but the filter
> >_is_ fully open". I've not heard anybody else mention this so
> >maybe it's just me.
> 
> my miniwave?

Monowave, sorry. :-) That was one of the two units you brought at
the 2002 PPG meet.

-- 
André Majorel <amajorel at teaser.fr>
http://www.teaser.fr/~amajorel/