Gaussian Filter
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Hi,
i'm searching for a Gaussian Filter to filter an 1d trace (125 Hz, x-axis:time, y-axis:signal) with a cutoff=4 Hz. Is there a function in matlab?
Thanks for your efforts!
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Rick Rosson
2011-6-29
In the Signal Processing Toolbox, please try either filterbuilder or guassfir.
HTH.
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David Young
2011-6-30
A Gaussian filter does not have a sharp frequency cutoff - the attenuation changes gradually over the whole range of frequencies - so you can't specify one. This follows from the fact that the Fourier transform of a Gaussian is itself a Gaussian.
What you usually specify is the frequency at which you require a certain attenuation. This is inversely proportional to the "width" of the Gaussian in the temporal domain. (It's not really a width - again it's the time at which the curve drops to a certain fraction of its maximum.)
You can find the detailed formulae and a proper description of all this (better than will fit into a MATLAB Answers answer) in signal processing textbooks. There's a starting point on the web at the Wikipedia article.
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Rick Rosson
2011-6-30
Please review the function reference page in the MATLAB documentation:
doc gaussfir
This page provides information on how to specify the 3 dB points.
HTH.
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Michele Bertoni
2018-6-27
Hi to all, I'm a bit confused.... First of all, I can't understand why should I apply low-pass gaussian filter to digital (1-D such audio or else) signal.... I've always seen IIR Butterworth or similar, maybe is it a zero-phase?
Taking a look to Wikipedia gaussian filter page I can understand gaussian on both time and frequency domain have same shape, ok. St=sigma (in time domain) Sf=sigma (in frequency domain)
St*Sf=1/(2*pi) ok, clear.
It's also said Sf is equivalent to cut-off frequency, in this case: Fs = sampling frequency fc = cut-off frequency St = sigma (in time domain) in number of samples fc=Fs/(2*pi*St)
But in this case fc equals to -6dB, while it's used correction factor c for different cut-off value.
Ok, let's take fcarl example: Fs = 125Hz fc = 4Hz I get St = 5, so I need to take gaussian kernel from -5 to 5 (11 values), is this right? But about coefficient values? Thanks,
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