FFT (DSP Blockset)

Compute the FFT of the input.

Library

Transforms, in General DSP

Description

The FFT block computes the fast Fourier transform (FFT) of each input channel independently at each sample time. The block assumes that the input is an M-by-N frame matrix. Each of the N frames in the matrix contains M sequential time samples from an independent signal.

The illustration below shows a 6-by-4 matrix input:

The Number of channels parameter specifies the number of independent channels (columns), N, in the matrix. The output is complex and has the same dimension and sample rate as the input (i.e., the FFT is computed at M frequency points for each channel).

The FFT operation for a single-channel input (Number of channels = 1) is shown below.

The input frame size, M, must be a power of two. To work with other frame sizes, use the Zero Pad block to pad or truncate the input frame to a power-of-two length.

Dialog Box

Number of channels: The number of columns (frames) in the input matrix.