[sdiy] Imperfect VCO

[Theo]

These pages have some simple code examples
http://www.bluebear.org.uk/studio/cz101/cz_pd.html
http://hekta.iet.hist.no/~leifcr/sy77/sy-prog/sy-prog.html
Apparently their focus is on "Casio" PD where the PD replaces the function
of a filter, similar to "Yamaha" FM.

Basically you are just generating a sinewave at all times,
only the "frequency" changes between the rising and the falling part of the
sine.

HTH
Theo

BTW,
je zoekt niet toevalling een eind opdracht in de VA richting?


----- Original Message -----
From: Bert Schiettecatte <bert.schiettecatte at esat.kuleuven.ac.be>


> Hi Theo,
>
> Thanks for the interesting notes. I never heard of this phase distortion
> technique. Maybe this is a silly question, but can you explain in more
> detail how a sine wave can be PD to render a bandlimited sawtooth?
>
> Thanks
> bert
>
> -----Original Message-----
> From: owner-synth-diy at dropmix.xs4all.nl
> [mailto:owner-synth-diy at dropmix.xs4all.nl] On Behalf Of Theo
> Sent: zaterdag 2 augustus 2003 15:32
> To: Bert Schiettecatte; synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] Imperfect VCO
>
> The paper mentioned is not exactly the latest in the art.
> Just google for "band limited waveform generation" to find some other
> approaches.
>
> There is one method worth to mention that is little published about,
> probably because it is not interesting  enough from a math side.
>
> Phase distortion of a sine wave is lean on CPU load and gives rather
> good
> results.
> Indeed the same thing the pp from Casio did 15 years ago.
> One of the nice things is how flexible phase distortion is,
> classic Casio modulated from saw to sine but it does not end there.
> PD of a sinewave to get a variable saw <--> tri or saw <--> square is
> also
> possible.
> On the down side, you never get a "pure" saw wave,
> in the end every ramp fast or slow is a segment of a sine.
> The higher harmonics carry a bit less energy compared to a analogue saw.
>
> Just as with any other method, computing on a higher sample rate and
> then
> down sample would help to reduce aliasing.
> But even if you don't PD can out perform most other methods on the
> aliasing
> side.
>
> Theo
>
>
>
> From: Bert Schiettecatte <bert.schiettecatte at esat.kuleuven.ac.be>
>
>
> > >Dig up "Alias-Free Digital Synthesis of Classic Analog Waveforms" by
> > >Tim Stilson and Julius Smith to get an impression of how hard it
> really
> >
> > >is to produce a sawtooth or square wave in the digital domain with
> > >proper bandlimiting.
> >
> > Exactly, quite hard I have to say. But I don't think the approach
> taken
> > in this paper is the best computational load/quality wise. I sort of
> > have a feeling that oversampling the whole synth loop and then
> > downsampling in the end might be a better approach ...
> >
> > bert
> >
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