[sdiy] FW: Kawai K3 - Bandlimited Waveforms

[Plutoniq9 •]

For quite a while I've been working on a project to create custom waveform ROM's for the Kawai K3/K3m. 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), I've got PCM's samples working inside the K3, but because my waves lack band-limiting ( i just down-sample the original 512-byte wave), the higher octaves tend to alias to the point where they are unusable.

I've created a graphic showing frequency analysis of both the K3's bandlimited waves, and then my waves which simply downsample (w/no filtering) the original 512-byte waveform. I tried using a low-pass filter before resampling but the resulting waves are different then what the K3 shows. 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.

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?) secondly.....since I'm trying to use PCM waves, what can I do to at least reduce the aliasing in the higher octaves, just a steep low-pass filter before resampling?

Here's the graphic, I'd be definitely interested in hearing anyone's insight, cause this is starting to hurt my brain. The waveforms in this graph were playing at 22k.

http://img706.imageshack.us/img706/5253/k3wavebandlimitedvsnoba.jpg

thanks

ryan
 		 	   		  
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