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Overlap-Add/Save

This example shows how to filter a sinusoid using the Overlap-Add and Overlap-Save FFT blocks.

The overlap-add algorithm filters the input signal in the frequency domain. The input is divided into non-overlapping blocks which are linearly convolved with the FIR filter coefficients. The linear convolution of each block is computed by multiplying the discrete Fourier transforms (DFTs) of the block and the filter coefficients, and computing the inverse DFT of the product. For filter length M and FFT size N, the last M-1 samples of the linear convolution are added to the first M-1 samples of the next input sequence. The first N-M+1 samples of each summation result are output in sequence.

The overlap-save algorithm also filters the input signal in the frequency domain. The input is divided into overlapping blocks which are circularly convolved with the FIR filter coefficients. The circular convolution of each block is computed by multiplying the DFTs of the block and the filter coefficients, and computing the inverse DFT of the product. For filter length M and FFT size N, the first M-1 points of the circular convolution are invalid and discarded. The remaining N-M+1 points which are equivalent to the true convolution are "unrolled" as output by the Unbuffer block.

References

Overlap-Add Algorithm: Proakis and Manolakis, Digital Signal Processing, 3rd ed, Prentice-Hall, Englewood Cliffs, NJ, 1996, pp. 430 - 433.

Overlap-Save Algorithm: Oppenheim and Schafer, Discrete-Time Signal Processing, Prentice-Hall, Englewood Cliffs, NJ, 1989, pp. 558 - 560.

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