fft

Purpose

Computes a 1- or 2-D Fast Fourier transform.

Format

y = fft(x)
Parameters:x (NxK matrix) – The values used to compute the Fast Fourier transform.
Returns:y (LxM matrix) – where L and M are the smallest powers of 2 greater than or equal to N and K, respectively.

Examples

This is example uses the FFT to find the frequency component of a signal buried in a noise. The first section sets up the parameters for the signal of sampling frequency 1 kHz and a signal duration of 1.5 secs

// Sampling frequency
Fs = 1000;

// Sampling period
big_T = 1/Fs;

// Length of signal
L = 1500;

// Time vector
t = seqa(0, big_T, L);

Now form the signal given by

\[0.7*sin(2\pi50t) + sin(2\pi120t)\]
// Compute signal
s = 0.7*sin(2*pi*50*t) + sin(2*pi*120*t);

Corrupt the signal with zero-mean white noise:

// Add white noise
x = s + 2*rndn(L,1);

Finally, compute the Fourier transform:

// Compute Fourier transform
y = fft(x);

Remarks

This computes the FFT of x, scaled by \(1/N\).

This uses a Temperton Fast Fourier algorithm.

If N or K is not a power of 2, x will be padded out with zeros before computing the transform.

See also

Functions ffti(), rfft(), rffti()