|Signal Processing Toolbox|
Raised cosine FIR filter design
b = firrcos(n,F0,df,fs)
returns an order
b = firrcos(n,F0,df,fs,'
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
df/2 is between
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
b = firrcos(n,F0,df)
uses a default sampling frequency of
b interprets the third argument,
r, as the rolloff factor instead of the transition bandwidth,
r must be in the range
b designs either a normal raised cosine filter or a square root raised cosine filter according to how you specify of the string
'normal', for a regular raised cosine filter. This is the default, and is also in effect when the '
type' argument is left empty,
'sqrt', for a square root raised cosine filter.
b specifies an integer delay in the range
[0,n+1]. The default is
n/2 for even
(n+1)/2 for odd
b 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] 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:
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