[sdiy] Wavetable info

[Grant Richter]

on 12/31/03 2:46 PM, Tom Arnold at xyzzy at sysabend.org wrote:

> Can anyone point me at a description of the ROM formats common for things
> like the ProphetVS and the like?  I guess all I really need to know is the
> common sample size used, but if there's any compression that'd be
> interesting to know about also.
> 
> Thanks.

The Digisound VCDO used a 64 byte / 8 bit sample. Storing 32 waves in a 2K
EPROM. For the sake of simplicity, this corresponds to a sample time of 5.8
mS at a sample rate of 11 kHz.

Most common is a 128 byte / 8 bit sample. This was used by the Prophet VS
and Wave PPG instruments. Compression consists of storing 64 bytes of a
symetric wave (1,2,3...3,2,1). For the sake of simplicity, this corresponds
to a sample time of 5.8 mS at a sample rate of 22.05 kHz.

The Mini-Wave, Waveform City, Doepfer A-112 sample playback module use a
straight uncompressed 256 byte / 8 bit sample. For the sake of simplicity,
this corresponds to a sample time of 5.8 mS at a sample rate of 44.1 kHz.

Resampling the waveforms is not recommended as most of the character is from
aliasing. For example, if you get a waveform image from a VS or PPG EPROM,
you can write a simple QBASIC program to uncompress them and store two
copies to make a 256 byte wave. This will preserve the original "buzziness".
Resampling via Sound Forge mellows them out a lot.

I've got the JD-800 waveform ROM bit images, but no clue as to how to read
them. Not straight PCM, that's for sure.

256 byte Wavetable editor & librarian is at:

http://www.wiard.com/support/support.html

under "Software".