[LAU] Frequency-response analyzer for Linux?

Ken Restivo ken at restivo.org
Fri Jul 17 19:47:17 EDT 2009

On Tue, Jul 14, 2009 at 04:13:13PM -0700, Justin Smith wrote:
> On Tue, Jul 14, 2009 at 3:56 PM, Fons Adriaensen<fons at kokkinizita.net> wrote:
> > 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
> > http://www.kokkinizita.net/linuxaudio/downloads
> >
> > The filter plugins are in the MCP set.
> >
> > --
> > FA
> I used japa years ago, but forgot its name, thanks for this excellent
> piece of software, which I am excited to have rediscovered.

Mille grazie! I've got JAPA going on two platforms, but I've got to apologise for being a bit dense in figuring out how to use it.

The UI looks a bit like an HP oscope, but, alas, i'm not much of an engineer, so I'm not sure to start. Is there a quick simple tutorial somewhere on how to use it? Anyone care to give me a few sentences of advice?

I basically want to put white noise through some filters (prolly using JACK-RACK), and view the frequency response of it. Looks like JAPA already has a built-in white an pink noise generator, which is nice. What would I connect to what (using i.e. using jack_connect) and how would I set up the switches and control on JAPA to do this? A simple screenshot of the correct setup might be enough to get me going.

Thanks again!


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