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From: Jerry Avins on 14 Jan 2010 15:40
Clay wrote:
> On Jan 14, 3:20 pm, Jerry Avins <j...(a)ieee.org> wrote:
>> Lane wrote:
>>> I'm implementing an algorithm for detecting heartbeats within an EKG
>>> signal. There is an initial filtering pass that is described in the
>>> paper like this: "In our implementation a 27 tap linear phase FIR
>>> filter is used. The cut-off frequencies are 18 Hz and 35 Hz." Our
>>> data is sampled at 256 Hz. I know this should be simple for a DSP
>>> expert, but I don't have the first clue how to compute the
>>> coefficients for such a filter. Can someone tell me what they are?
>>> And then tell me what formula you used so I don't have to bother this
>>> group again? Thanks a million.
>> From the two cutoff frequencies, I assume that what is described is a
>> band-pass filter. It is nevertheless a description, not a specification.
>> Even knowing the number of taps, trade-offs can be made between the
>> sharpness of cutoff, the attenuation in the stop band, and the ripple in
>> the passband. For these, I suggest that you ask the authors of the paper.
>>
>> For coefficient calculation, you might likehttp://www.dsptutor.freeuk.com/FIRFilterDesign/FIRFilterDesign.html. It
>> assumes a 8,000 Hz sample rate, so you must scale your band edges by
>> 8000:250, or 32:1. The silly Java program does only even taps. 26 or 28
>> ought to work fine. There are better programs, but this one is to hand.
>> A quick look tells me that the stopband attenuation with fewer than 40
>> taps will be poor with this windowed-sinc design. You might want to
>> download a free trial copy of ScopeFIR fromhttp://www.iowegian.com.
>>
>> Jerry
>> --
>> Engineering is the art of making what you want from things you can get.
>
> Hey Jerry, try out my program - it is free and will certainly let you
> do even or odd numbers of taps.
>
> http://www.claysturner.com/dsp/fir.zip

Thanks. It's downloaded.

Jerry
--
Engineering is the art of making what you want from things you can get.
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