I hope that someday Octave will include more signal processing
functions. If you would like to help improve Octave in this area,
fftconv (a, b, N)
length (a) + length (b) - 1. If a and b are the coefficient vectors of two polynomials, the returned value is the coefficient vector of the product polynomial. The computation uses the FFT by calling the function
fftfilt. If the optional argument N is specified, an N-point FFT is used.
fftfilt (b, x, N)
fftfiltfilters x with the FIR filter b using the FFT. Given the optional third argument, N,
fftfiltuses the overlap-add method to filter x with b using an N-point FFT.
filter (b, a, x)
[y, sf] = filter (b, a, x, si)
filteruses the argument si as the initial state of the system and and returns the final state in sf. The state vector is a column vector whose length is equal to the length of the longest coefficient vector minus one. If si is not set, the initial state vector is set to all zeros.
[h, w] = freqz (b)returns the complex frequency response h of the FIR filter with coefficients b. The response is evaluated at 512 angular frequencies between 0 and The output value w is a vector containing the 512 frequencies.
[h, w] = freqz (b, a)returns the complex frequency response of the rational IIR filter whose numerator has coefficients b and denominator coefficients a.
[h, w] = freqz (b, a, n)returns the response evaluated at n angular frequencies. For fastest computation n should factor into a small number of small primes.
[h, w] = freqz (b, a, n, "whole")evaluates the response at n frequencies between 0 and