[sdiy] String filters and divide down oscillator string synths

[Dan Snazelle]

when you say divide down, i assume you mean an top octave generator. what are you using to acheive this?? as far as i can tell, these chips are now impossible to buy
--------------------------------------------
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> Date: Sat, 21 Jun 2008 13:36:56 +0100
> From: andylist at vellocet.com
> To: jhaible at debitel.net; synth-diy at dropmix.xs4all.nl
> CC:
> Subject: [sdiy] String filters and divide down oscillator string synths
>
> Hey JH!
>
> Great work on the string filter.
>
> I'm working on a digital emulation of a classic divide down string
> synthesizers at the moment, and as far as possible I am sticking to what
> is realistic to do in the analog world. I already have a divide down
> sawtooth oscillator with adjustable one pole high pass to generate the
> main buzz. I am now looking at the further processing involved to make
> it more string like.
>
> I have checked several schematics for their formant filters to emulate
> the body of a string instrument or piano and so far have been pretty
> disappointed. I am going to construct my own filters based on whatever
> literature I can find and hand tuning the coefficients to get something
> that sounds as close to a sample of the instrument as I can get. I plan
> on approximating the lower resonances with four 2 pole filters, and
> currently I'm tossing up between a couple of designs:
>
> * 4 parallel band pass filters with adjustable freq, res, and gain
> * 1 high pass and low pass in series with freq, res and single gain in
> parallel with a band pass filter with adjustable freq, res, and gain,
> and then all that in series with a notch filter with freq and res.
>
> Do you have any suggestions as to other possible designs? Do you know of
> any links to any pages that have formant shapes for instruments?
>
> I have done some research in the Arp Omini (I have one sitting in front
> of me to test with) which others might be instereseted in (sorry if this
> is all obvious stuff that everyone already knows)
>
> * To get a saw from a sqr divide down sqr wave you high pass filter the
> sqr then clip off the bottom with a diode then high pass again.
> * The "amp" per note is achieved by varying a bias voltage to the diode
> so the clip point changes. This results in some "thumping" with note ons
> since the dc introduced has to be filtered away.
> * The "hollow" or waveform enhancement mode is made by moving the bias
> voltage enough that the other spike of the high pass sqr waveform is
> present in the output signal.
> * Since the amp per voice is made by varying the bias voltage for the
> clip you get timbral variations through the attack and release.
> * The "string" sections simply put this waveform through a chorus.
>
> All the best,
>
> Andrew Simper
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