Wavetable software

[Grant Richter]

The software elves are currently redesigning the Wiard waveform generation
software to support any sample length, bit depth and multiple file formats.
The intention is to supply a generalized tool to support various wavetable
hardware formats, MAX MPS and Csound. The new version should be cross
platform also (no more Win32 calls).

The current revision is a Win32 app that is specifically targeted at 64K
wavetables (256 waves of 256 samples) and 8 bits.

I will be putting up the generation software on the Wiard site this
coming week on a shareware basis. The new software will replace it
when it is out of beta. For smaller wavetable sizes (64 samples) you can do
a little manual "decimation" filtering and just eliminate 3/4 of the
samples.

Try to imagine the wavetable units forming a continuous spectrum
from the very lowest 4 bit R-2R sine shaper out to 24 bit 96Khz waveforms.

In a software generation scheme, the sample rate is fixed and the waveforms
are resampled to produce different output pitches. This works out very well
mathematically and sideband products are easy to control. Even a Mirage
or ESQ (8 bit) does a pretty good job of it.

In a hardware wavetable configuration, the sample rate of the entire system
is
modulated and this does NOT work out mathematically. Any combination of 
bit depth or bit rate will at some circumstance produce audible artifacts.
This is actually quite usable musically, since after filtering and
enveloping etc.
the artifacts are just part of the tone.

Try not to get too hung up on the technicalities of the generator. Even
though
the Wiard oscillator supports 256 samples, I still use waveforms "reduced"
to 64 samples just to get that sound!

Having built all three type of VCDO let me kick in my $.02 The three
methods are:

1. Direct clocking of a counter with a HF VCO.
	Good: Tight
	Bad: Designing a VCO in the low RF is tough and you only get the wave
	table output, direct VCO out is too high to use.
2. Phase lock a HF VCO to a regular one.
	Good: Now you can use regular VCO out at the same time as wavetable out.
	Bad: Boingy-Spoingy noises and portamento. Tuning a PLL loop filter
	to operate from 20Hz to 10Khz is an engineering project in itself. You
	end up putting a VCF in the loop and it gets real expensive. Never could
	eliminate that last trace of portamento.
3. Use high speed A/D as address generator for wavetable.
	Good: Tight,Easy, ADC0820 is $4.86 from Digikey. Easy to go to 1024
samples with 10 bits.
	Analog oscillator outputs available at same time. Can use unit as
quantizer.
	Bad: Hard to push above 5Khz, but then your second harmonic is at 10Khz
anyway.

----------
> From: jbv <jbv.silences at wanadoo.fr>
> To: synth-diy at mailhost.bpa.nl
> Subject: Waveshaper again
> Date: Thursday, April 15, 1999 6:24 PM
> 
> Paul Schreiber :
> 
> > Grant Richter has been doing this for years.
> >
> > www.wiard.com
> >
> > see: Waveform City
> >
> 
> I knew I was re-inventing the wheel !        ;-)
> 
> Anyway, the Wiard stuff looks great, but at $395, I think it is worth
> brainstorming a little bit
> more and try to design my own thing.
> 
> Below are a few more questions :
> 
>     - what kind of waveforms would you like to see in a waveshaper and in
a
> VCDO (apart from the
> regular sine, tri, etc) ?
> 
>     - are 64 bytes enough for each waveform ?
> 
>     - are 8 bits enough for the ROM data outputs (sent to the DAC) ?
> 
> Thanx.
> 
> jbv