Explain overlap-add and overlap-save methods for fast convolution.

Both methods use FFT for efficient convolution of long signals with shorter filters. Overlap-Add: Divide input into non-overlapping blocks, FFT-convolve each with filter, results overlap and are added. Overlap-Save: Divide input into overlapping blocks, FFT-convolve, discard corrupted samples from circular convolution, save valid portion. Both achieve O(N*log(N)) complexity vs O(N*M) direct convolution. Choice depends on implementation: overlap-add has simpler input handling, overlap-save avoids explicit addition. Block size selection balances FFT efficiency vs latency. Essential for real-time processing of long signals.