Signal Processing

I hope that someday Octave will include more signal processing functions. If you would like to help improve Octave in this area, please contact bug-octave@che.utexas.edu.

fft (a)

Compute the FFT of a using subroutines from FFTPACK.

fft2 (a)

Compute the two dimensional FFT of a.

fftconv (a, b, N)

This function returns the convolution of the vectors a and b, a vector with length equal to the 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)

With two arguments, fftfilt filters x with the FIR filter b using the FFT. Given the optional third argument, N, fftfilt uses the overlap-add method to filter x with b using an N-point FFT.

filter (b, a, x)

This function returns the solution to the following linear, time-invariant difference equation: where An equivalent form of this equation is: where In terms of the z-transform, y is the result of passing the discrete- time signal x through a system characterized by the following rational system function: When called as

[y, sf] = filter (b, a, x, si)

filter uses 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.

freqz

Compute the frequency response of a filter. [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

ifft (a)

Compute the inverse FFT of a using subroutines from FFTPACK.

ifft2

Compute the two dimensional inverse FFT of a.

sinc (x)

Returns