[sdiy] String filters and divide down oscillator string synths

[cheater cheater]

>  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.

Don't forget the analog instruments were limited in what they could do
by the fact that they were analog, and that since you're doing DSP you
can achieve similarly functioning, but different, better, results
through 'beauty of simple design'. Don't that hard to copy, just use
your ears and judge whether the result is suitable for the general
feel of a string synth.
Or I'll come by sometime after monday and we can use my ears, which is
probably going to be much more fun. :)


>  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?

Moog APF

If you clone JH's string filter into digital before the analog version
is ready, I'm going to die.

D.

On 6/21/08, Andrew Simper <andylist at vellocet.com> wrote:
> 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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