Re: [Linuxsampler-devel] Gigasampler filter analysis

[ian e. <de...@cu...>]

the impulse response of a filter completely describes its frequency
response... what other information do you need?


On Wed, 2003-10-29 at 16:39, Steve Harris wrote:
> 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
> 
> 
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