[Eeglablist] pop_resample kaiser window question

Andreas Widmann widmann at uni-leipzig.de
Thu May 2 05:27:04 PDT 2019


Hi Russell,

> In the pop_resample function on line 284: b = firws(m, fc, windows('kaiser', m + 1, 5)); % Anti-aliasing filter kernel
> 
> Is the value of beta for the kaiser window supposed to be 5 as it is or is it supposed to be 0.5 as is the default in the matlab Kaiser function?
It is supposed to be 5 as it is. You may compute dev from beta inverting the equations (see invkaiserbeta function from firfilt plugin). You will then notice that beta = 0.5 will give you a stopband attenuation of -21 dB what is not a sensible choice for an anti-aliasing filter. Our default beta = 5 (dev = 0.002) will give you a stopband attenuation of -54 dB what I would consider a reasonable compromise between filter order and anti-aliasing. This is the same attenuation a Hamming window (FIR sinc filter) would give you but with considerably lower filter order (filter length) using Kaiser instead of Hamming window.

Hope this helps! Best,
Andreas

> Thanks much!
> 
> Very respectfully,
> 
> Russell T. Toll, Ph.D.
> Assistant Professor
> Department of Psychiatry
> Center for Depression Research and Clinical Care
> UT Southwestern Medical Center
> 6363 Forest Park Rd, Suite BL 13.206
> Dallas, TX 75235-5479
> 
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