Matlab, fdesign, sample rate

Question

I am using the function fdesign.lowpass in Matlab, on a signal that is sampled at 8kHz. I am making a filter for a speech signal and want to filter out gaussian noise, i have found the fundamental freq. to be around 343Hz with FFT.

So I am using the command in Matlab:

fdesign.lowpass('Fp,Fst,Ap,Ast',319,378,0.25,1,8000);

Should my sample rate be 8000/2?

score 0 · Answer 1 · answered Oct 14 '16 at 14:54

0

Should my sample rate be 8000/2?

No, the Fs argument should be the actual sampling rate, so in your case 8000. The other frequency arguments would then be interpreted to be in Hz and should then be less than 8000/2 (which is what you have now).

Note also that I doubt that you only want 1dB of stopband attenuation as specified with Ast if you want to see any sort of significant out-of-band noise reduction. Also, you might want to increase your passband cutoff frequency (Fp) to actually include your signal's fundamental frequency (and perhaps a few harmonics as well, depending on your application).

answered Oct 14 '16 at 14:54

SleuthEye

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' fdesign.lowpass('Fp,Fst,Ap,Ast',1000,1600,1,50,8000); ' – AprilDC Oct 15 '16 at 21:03
' fdesign.lowpass('Fp,Fst,Ap,Ast',1000,1600,1,50,8000); ' Does that look better? – AprilDC Oct 15 '16 at 21:03
That's more in line with what I'd expect for a typical application. – SleuthEye Oct 16 '16 at 00:17

Matlab, fdesign, sample rate

1 Answers1