Subject: Re: [linux-audio-dev] Re: Moog VCF in SpiralSynthModular
From: Dr. Matthias Nagorni (mana_AT_suse.de)
Date: Mon May 27 2002 - 11:47:33 EEST
On Sat, 25 May 2002, Juhana Sadeharju wrote:
> changes change the response. I tuned one of moog filters
> manually and it needed only slight modifications. I don't
Well, do you perhaps remember these modifications ?
> I wrote a simple code for searching the peak of the frequency
With my KWaveView spectrum analyzer I have a good tool for this.
> A look-up table could be a bad thing nowadays.
Indeed.
> Were are all those mentioned filters available as your source code?
Check m_vcf.cpp
> were there. Could you add documentation to your filter codes?
They are all taken from the cookbook formulae by Robert Bristow-Johnson.
I intentionally kept his naming of variables, so you can compare with his
paper. BTW I mention the sources for the filter formulae in the THANKS
file and , as far as I remember, also in the mail you replied to:
http://www.harmony-central.com/Computer/Programming/Audio-EQ-Cookbook.txt
> If you mail me all your filter implementations, I will document
> them myself.
What I would still need is more documentation on parameter ranges
(especially dbGain and Q). This is not mentioned in the cookbook paper.
> It is actually a good idea to not implement LADSPA etc. plug-ins
> in the first place, specially if one is not used to programming
> those. I have written filters with simple API: void *filter_new(),
> filter_init(), filter_set_parameter(), float filter_do(float) etc.
OK, then you will perhaps like http://www.dspguru.com/sw/lib/biquad.c
by Tom St Denis.
> only the essential is in the filter code (no need for KDE for
> compiling, for example). An optimized versions can be written later
None of my programs does require KDE for compiling. I planned to implement
them as KDE programs (therefore the confusing "K") but then changed this
because KDE would not add much benefit.
Matthias
-- Dr. Matthias Nagorni SuSE GmbH Deutschherrnstr. 15-19 phone: +49 911 74053375 D - 90429 Nuernberg fax : +49 911 74053483
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