GIC String Filter - first experiments (was: [sdiy] Filter Banks & CSound)

[jhaible]

Hi,

I've finally made my own version of a String Filter Bank.
Samples from some first experiments are avaiable at
http://home.debitel.net/user/jhaible/jh_string_filter.html

I think the peak/valley ratio of the main filter bank is ok,
but the air/wood/bridge resonance needs some more
adjustments. Any hints how to improove this are welcome.
(Benade gives detailed information about the frequency -
125Hz, 175Hz, 1.5kHz and 2kHz for Cello -, but not
about Q and Gain.)

JH.





-----Ursprüngliche Nachricht-----
Von: Ian Fritz <ijfritz at earthlink.net>
An: Tim Ressel <madhun2001 at yahoo.com>
Cc: <synth-diy at dropmix.xs4all.nl>
Gesendet: Mittwoch, 11. Dezember 2002 04:26
Betreff: Re: [sdiy] Filter Banks & CSound


> Tim --
>
> Filter bank references:
>
> "Electronic simulation of violin resonances," JV Mathews and J Kohut, J.
> Acoust. Soc. Am., vol. 53, 1620 (1973).
>
> "Audio engineering improvements for clavichords," RW Burhans, J. Aud. Eng.
> Soc., vol. 23, 635 (1975).
>
> "Filter bank design," IJ Fritz, Electronotes, #107, 16 (1979).
>
> "A 39-channel variable-Q filter bank," BA Hutchens, Electronotes, #115, 3
> and #116, 3 (1980).
>
> It's the peak-to-valley ratio that mainly characterizes the overall
> sound.  This ratio is strongly influenced by the shape of the resonance
> curves and the number of resonators, since many long tails can add up to
an
> appreciable contribution.
>
> I used a single transistor circuit for my resonators -- just a phase-shift
> oscillator with a bit of degeneration to set the Q.  I started with
nominal
> Q values around 20, but had to increase this somewhat to get 10 dB
contrast
> with all the bands turned up.  My design has variable amplitude on each
> filter and variable Q in sub-banks of six frequencies.  That way I can --
> for example -- do some formant shaping at low frequencies and timber
> enrichment at high frequencies at the same time.
>
> The hollow, echoey sound you describe is from too large a peak-to-valley
> ratio.  Several people have remarked on this before.
>
>    Ian
>
>
> At 07:50 PM 12/10/2002, Tim Ressel wrote:
> >Ian,
> >
> >Yes, in fact Dr. Matthews was mentioned in the
> >article. I'd love to see the article if you can lay
> >your paws on it.  What kind of filters are in your
> >filter bank? What frequencies and Qs??
> >
> >By the by, the CSound filters I used did not seem to
> >parallel well. I didn't get that timbre change for
> >slight frequency changes. Also the bank had a hollow,
> >echo like sound. If I knew the real filters used I
> >might be able to get it working better.
> >
> >--tr
>
>