Overlap-Save FFT Filter (Obsolete)
Implement overlap-save method of frequency-domain filtering
Filtering / Filter Implementations
The Overlap-Save FFT Filter block has been replaced with the Frequency-Domain FIR Filter block. Existing instances of the Overlap-Save FFT Filter block continue to run.
The block accepts vector or matrix inputs, and treats each column of the input as an individual channel. The block unbuffers the input data into row vectors such that the length of the output vector is equal to the number of channels in the input. The data output rate of the block is M times faster than its data input rate, where M is the length of the columns in the input (frame-size).
Overlapping sections of input
u are circularly convolved
with the FIR filter coefficients
The numerator coefficients for H(z)
are specified as a vector by the FIR coefficients
parameter. The coefficient vector,
b = [b(1) b(2) ...
b(n+1)], can be generated by one of the filter design
functions in the Signal Processing Toolbox™ product, such as
fir1. All filter states
are internally initialized to zero.
When either the filter coefficients or the inputs to the block are complex,
the Output parameter should be set to
Complex. Otherwise, the default
Real, instructs the block to take only the real
part of the solution.
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 you specify
nfft in the FFT size
parameter as a power of two value greater (typically
much greater) than
Values for FFT size that are not powers of two are
rounded upwards to the nearest power-of-two value to obtain
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
In single-tasking operation, the Overlap-Save
FFT Filter block has a latency of
samples. The first
nfft-n+1 consecutive outputs
from the block are zero; the first filtered input value appears at
the output as sample
In multitasking operation, the Overlap-Save FFT
Filter block has a latency of
samples. The first
outputs from the block are zero; the first filtered input value
appears at the output as sample
- FFT size
The size of the FFT, which should be a power of two value greater than the length of the specified FIR filter.
- FIR coefficients
The filter numerator coefficients.
The complexity of the output;
Complex. When the input signal or the filter coefficients are complex, this should be set to
Oppenheim, A. V. and R. W. Schafer. Discrete-Time Signal Processing. Englewood Cliffs, NJ: Prentice Hall, 1989.
Proakis, J. and D. Manolakis. Digital Signal Processing. 3rd ed. Englewood Cliffs, NJ: Prentice-Hall, 1996.
Supported Data Types
Double-precision floating point
Single-precision floating point
|Overlap-Add FFT Filter||DSP System Toolbox|