[sdiy] FW: Kawai K3 - Bandlimited Waveforms

[Tom Wiltshire]

Ryan,

>  After figuring out their crazy ROM format (dual ROM's w/ 6  
> interleaved octaves in each 1k space (512-byte, 256-byte, 128-byte,  
> 64-byte & two 32-byte waveforms), second ROM is the derivative of  
> the first)

Interesting. I wonder what they use the derivative for. Interpolation  
between samples?
I've used tables which included the derivative sometimes, because it  
can be quicker to simply read it and multiply by the interpolation  
index, rather than work out an index, get the lower sample from the  
table, work out the next index (it could have wrapped around), get  
the higher sample from the table, take the lower from the higher, and  
THEN multiply by the interp index.

> It's making me think that the K3's waveforms were created using  
> Fourier synthesis, because they seem to be just reducing individual  
> harmonics over nyquist.

That's a pretty straightforward way to do it, no?
Couldn't you write a script that takes a list of harmonic amounts and  
spits out the necessary wavetables and derivative tables?

> I have a question, how come normal wavetable synths don't need to  
> go to this extent to reduce aliasing in the higher octaves  
> (normally they just use a single waveform right?)

That's the difference between the two schemes for wavetable  
oscillators. As Chris Meyer (Ex-Sequential) says in his piece about  
the birth of the Prophet VS:
"Tony and I theorized on how to do a wavetable synth, and came up  
with two strategies - have a
waveform of short, fixed length and vary how fast you played it, or  
start with a very long
version of a waveform and skip samples in it to alter how long it  
took you to read it out once
(and therfore alter your final pitch). Unable to decide we acquired a  
PPG and a Korg DW6000 to
see how they did it. We felt vindicated to learn that the PPG did it  
exactly the first way we
theorized, and the Korg the second."

http://www.vintagesynth.com/sci/birth.txt

The K3 is obviously using the second method, like the Korg DW. The  
"normal" wavetable synths you mention (made by PPG/Waldorf, right?)  
use the first.

Regards,
Tom