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Thread Subject:
design filter

Subject: design filter

From: ghazale

Date: 11 Oct, 2013 10:15:05

Message: 1 of 2

In MATLAB I have to pass cut-off frequency for designing a filter. But this Cut-off frequency is in radians-per-sample. How do I convert my analog Cut off frequency in Hz, into the required radians-per-sample for MATLAB?

Subject: design filter

From: Wayne King

Date: 11 Oct, 2013 13:31:05

Message: 2 of 2

"ghazale " <ghazale.boroumand@gmail.com> wrote in message <l38j39$1m1$1@newscl01ah.mathworks.com>...
> In MATLAB I have to pass cut-off frequency for designing a filter. But this Cut-off frequency is in radians-per-sample. How do I convert my analog Cut off frequency in Hz, into the required radians-per-sample for MATLAB?

If you know the frequency in Hz and the sampling frequency you can do it easily.

Assume that T = 1/(sampling frequency), in other words, T is the sampling interval.

To convert your frequency in Hz to radians/sample

f*(2*pi*T)

The above gives you the frequency in radians/sample. For example, assume the sampling frequency is 1000 Hz and the frequency you want to convert is 100 Hz.

The equivalent frequency in radians/sample is

100*(2*pi*0.001)

Note that in designing filters, MATLAB often uses normalized frequency where a factor of pi is factored out, so that 1 is actually pi.

That means that the above would actually be:

(100*2*pi*0.001)/pi

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