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IIR/FIR external & Freq Response


J
January 13, 2008 | 7:36 pm

Hi there,

I am currently coding various IIR and FIR filters using co-effecients from MATLAB for bandpasses at very low frequencies (0 -40 Hz) with very small bandwidths (around 6 Hz).

However once I have them coded is there any real way within Max to view the freq/magnitude response of my filters?

Also if I put the Spectroscope~ within a downsampled poly~ will the frequency resolution increase accordingly?

thanks
J


January 14, 2008 | 7:55 pm

On 13 Jan 2008, at 19:36, Jam wrote:

>
> Hi there,
>
> I am currently coding various IIR and FIR filters using co-
> effecients from MATLAB for bandpasses at very low frequencies (0
> -40 Hz) with very small bandwidths (around 6 Hz).
>
> However once I have them coded is there any real way within Max to
> view the freq/magnitude response of my filters?

well, from the coefficients you could derive the filter transform
function and from this calculate the freq response, but you
probably want to meassure the response to verify your code, right?

so why not send a unit impulse (click~) into your filter and record
the output into a buffer?
then do an fft on the buffer to view the freq response.

with very narrow bandpasses the impluse response can get quite long.
also for low frequencies you would need very large fft sizes…
somewhere i have an external lying around that performs ffts of long
buffers (nonrealtime ) that i would be happy to share.
it only needs a help file.
but this is for osx only.

volker.


January 14, 2008 | 8:57 pm

Me too this been for a while i’ve been looking for an FFT of long size, so a sharing of this external is very welcomed !

Salvator



kjg
January 14, 2008 | 10:30 pm

Would you consider putting on maxobjects.com, Volker?


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