Subject: Re: [linux-audio-user] notch/peak? filters ladspa question.
From: Dr. Matthias Nagorni (mana_AT_suse.de)
Date: Tue Jun 04 2002 - 16:20:58 EEST
On Tue, 4 Jun 2002, Marco Scoffier wrote:
> The ladspa plugins suffer from this sort of confusion about what the
> ranges are actually doing. Perhaps I haven't been reading the right
Recently I implemented the filters found at
and a resonant lowpass filter by Paul Kellett as LADSPA plugins:
You will probably be interested in the notch filter and the two bandpass
"make" will create two .so files where vcf.so has single audio in/out.
vcf_cv_in.so has additional audio rate inputs for dynamic frequency and
resonance control as used in softsynths. Probably you will only need
vcf.so. The parameters are as follows:
Gain: Gain factor for input signal.
Frequency Offset: Cutoff Frequency (in vcf_cv_in.so this offset is added to
the frequency_in signal).
Frequency Pitch: -2 will divide, +2 multiply the cutoff frequency by a factor
of 2. This is especially useful for softsynths (like e.g.
AlsaModularSynth), where you could bind a MIDI pitchbender
controller to this control.
Resonance Offset: This is Q between 0.001 and 1.0. In the cookbook filters,
I multiply this Q by a factor of 32.0 to obtain the Q value
which I insert in the formulae. You could change this by
modifying Q_SCALE (this absorbs another factor of 2.0,
therefore at the moment it's 64.0). The Q of the simple
resonant lowpass filter by Paul Kellett is normalized
between 0 and 1 anyway.
dBgain Offset: This is dBgain for the peaking EQ and shelving filters.
Please note that at high dBgain some frequencies will cause
overflows. I'll fix this in a future version.
BTW I might not be able to read email until next Monday, since I travel to
-- Dr. Matthias Nagorni SuSE GmbH Deutschherrnstr. 15-19 phone: +49 911 74053375 D - 90429 Nuernberg fax : +49 911 74053483
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