User`s guide

Overlap-Save FFT Filter
5-335
The circular convolution of each section is computed by multiplying the FFTs
of the input section and filter coefficients, and computing the inverse FFT of
the product.
y = ifft(fft(u(i:i+(L-1)),nfft) .* fft(b,nfft))
where nfft is specified by the FFT size parameter as a power-of-two value
greater (typically much greater) than
n+1. Values for FFT size that are not
powers of two are rounded upwards to the nearest power-of-two value to obtain
nfft.
The first
n points of the circular convolution are invalid and are discarded. The
Overlap-Save FFT Filter block outputs the remaining
nfft-n points, which are
equivalent to the linear convolution.
Latency
In single-tasking operation, the Overlap-Save FFT Filter block has a latency of
nfft-n+1 samples. The first nfft-n+1 consecutive outputs from the block are
zero; the first filtered input value appears at the output as sample
nfft-n+2.
In multitasking operation, the Overlap-Save FFT Filter block has a latency of
2*(nfft-n+1) samples. The first 2*(nfft-n+1) consecutive outputs from the
block are zero; the first filtered input value appears at the output as sample
2*(nfft-n)+3.
See “Excess Algorithmic Delay (Tasking Latency)” on page 3-91 and “The
Simulation Parameters Dialog Box” in the Simulink documentation for more
information about block rates and Simulink’s tasking modes.
Dialog Box