[LAU] Frequency-response analyzer for Linux?

Fons Adriaensen fons at kokkinizita.net
Tue Jul 14 18:56:50 EDT 2009

On Tue, Jul 14, 2009 at 03:25:39PM -0700, Justin Smith wrote:

> Try running a white noise source through the filter, then look at the
> spectral graph output in your favorite spectrum analysis program.
> Since white noise should have a flat spectrum, any peaks and valleys
> in the output are those of the filter.

For a more 'musical' analysis, use Japa. It has either 
a logarithmic or perceptual frequency scale. Pink noise
source is built-in, and if you set the analyser response
to 'Proportional' it will show a flat spectrum for pink
noise. It can also show the difference between two spectra,
e.g. input and output of a filter, and this produces much
more stable displays when using a noise test signal.

For the filter, you could try on of the four Moog VCF
plugins I wrote years ago. Apart from the resonant
lowpass they will also add some juicy distortion at
high levels, as does the original Moog filter and
probably all real analog Wah processors. Frequency
control is logarithmic, which is probably what you
want, and there are separate control inputs to 
set the static frequency and resonance and their
modulation. One problem could be that the modulation
inputs require audio rate signals (the filter were
designed for use in AMS) but that can be changed
easily if you want. If you want to play with them
use AMS.

But Japa and the filters to be found at 

The filter plugins are in the MCP set.


Io lo dico sempre: l'Italia è troppo stretta e lunga.

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