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Raised cosine FIR filter design



b = firrcos(n,F0,df,fs) or, equivalently,

b = firrcos(n,F0,df,fs,'bandwidth') returns an order n lowpass linear-phase FIR filter with a raised cosine transition band. The filter has cutoff frequency F0, transition bandwidth df, and sampling frequency fs, all in hertz. df must be small enough so that F0 ± df/2 is between 0 and fs/2. The coefficients in b are normalized so that the nominal passband gain is always equal to 1. Specify fs as the empty vector [] to use the default value fs = 2.

b = firrcos(n,F0,df) uses a default sampling frequency of fs = 2.

b = firrcos(n,F0,r,fs,'rolloff') interprets the third argument, r, as the rolloff factor instead of the transition bandwidth, df. r must be in the range [0,1].

b = firrcos(...,'type') designs either a normal raised cosine filter or a square root raised cosine filter according to how you specify of the string 'type'. Specify 'type' as:

b = firrcos(...,'type',delay) specifies an integer delay in the range [0,n+1]. The default is n/2 for even n and (n+1)/2 for odd n.

b = firrcos(...,'type',delay,window) applies a length n+1 window to the designed filter to reduce the ripple in the frequency response. window must be a length n+1 column vector. If no window is specified, a rectangular (rectwin) window is used. Care must be exercised when using a window with a delay other than the default.

[b,a] = firrcos(...) always returns a = 1.


Design an order 20 raised cosine FIR filter with cutoff frequency 0.25 of the Nyquist frequency and a transition bandwidth of 0.25:

See Also

fir1, fir2, firls, firpm

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