[Linuxsampler-devel] Gigasampler filter analysis

[Steve H. <S.W...@ec...>]

Thanks to Mark for running the impulses through the filters, sadly there
isn't enough inforamtion in the impulse (maybe due to some noise that
crept in somewhere, maybe due to some non linearity in the filter, to be
honest I dont know why) to analyse them, eg here are 4 traces from the
lowpass filters:

http://www.ecs.soton.ac.uk/~swh/gst-impulses/

They are the highest resonance settings, 4 different frequencies, which
are the clearest, but still dont have much information in them.

Mark, if possible could run run a very good whitenoise source (I can
provide a WAV if you need one) into the same filters, runnning them a
couple of seconds at each setting? Sorry, I didnt realise the signal
would be so noisy.

Just at minimum resonance settings with the 4 cutoffs you used before will
be great for starters.

As a note for me, and incase anyone wants to try it, you can produce
spectrum plots in octave easily:

1) chop out the signal into sections to analyse (preferably just over 1
   sec) with no other signal in them. save as 16bit mono WAV (eg. 01.wav)

2) convert to raw PCM file (eg. sox 01.wav 01.raw)

3) octave stuff:

$ octave
octave:1> # produce an fft of the raw file
octave:1> f = fft(loadaudio('01', 'raw'), 44100);
octave:2> # plot the freq response
octave:2> plot(abs(f(1:22050)/max(abs(f))));

the plot is frequency (Hz) on the x-axis and normalised amplitude on the
y-axis.

plot(20.0 * log(abs(f(1:22050)/max(abs(f))))/log(10));
will show amplitude in dB's, which can be helpful.

- Steve