[sdiy] Casio CZ resonant waveforms / Windowed Sync

[Scott Nordlund]

> I've been messing with using the windowed sync technique that Casio used for 'resonant waveforms' on the CZ synthesizers:
>
> http://www.electricdruid.net/images/cz/czresonantwaves.mov
>
> (6.5Mb mov)
>
> The technique is described on the CZ wiki page, but the Deep Synthesis site has much more detail:
>
> http://en.wikipedia.org/wiki/Casio_CZ_synthesizers
> http://homepage.mac.com/synth_seal/html/cz1.html

Similar techniques were also used for formant synthesis in computer music in the 70's and 80's, with a few variations. It's helpful to play with window shape, and also to add multiple, independent windowed sines.

There are a lot of relevant patents, too: Casio's were 4658651 and RE34481 (reissue), and Yamaha had 4200021, 4259602, 5138927, 5610354. Yamaha did some similar things with variations of FM synthesis (4422362,
 4406204), and also a strange thing that windowed portions of a 
frequency swept
 sine wave (4282790, 4418600, 4393743, RE32862). I've also seen this 
described in a CMJ paper as "linear 
sweep synthesis". I played around with it some, but it doesn't seem 
terribly useful.

Interestingly, Yamaha appeared to have patented phase distortion very similar to what Casio used (4183275, 4223582, RE30834). So any litigation between Yamaha and Casio was probably over these patents rather than the CZ's supposed similarity to the DX7.