18 Jul
2009
18 Jul
'09
12:18 a.m.
On Fri, Jul 17, 2009 at 05:43:09PM -0700, Justin Smith wrote:
On Fri, Jul 17, 2009 at 4:47 PM, Ken
Restivo<ken(a)restivo.org> wrote:
Thanks.
I did as you suggested, and it worked! But I'm confused by the results.
This is straigtht pink noise directly from JAPA's generator back into its input... but
the frequency response appears not to be flat!
http://restivo.org/misc/pink.png
The white noise was similarly not flat:
http://restivo.org/misc/white.png
So, in terms of viewing the response of the filter, do I need to A/B or A-B to get some
kind of estimate of what the filter is doing?
-ken
On Tue, Jul 14, 2009 at 04:13:13PM -0700, Justin
Smith wrote:
Connect the pink output of japa to the input of the application with
the filter, connect the output of the app with the filter back into
japa, the curve you see in japa will be the frequency response of the
filter. Since japa can overlap displays, you can also try putting some
musical material through: one input straight into japa, one through
the filter first, and look at the compared spectrums.
Another possibility would be routing the japa pink output to an analog
wah pedal, and comparing the frequency response of the analog pedal
coming back in to the digital wah emulator. Or you could compare the
spectral output of the real and digital wahs with musical input. On Tue, Jul 14, 2009 at 3:56 PM, Fons
Adriaensen<fons(a)kokkinizita.net> wrote:
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!
-ken
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. 
