Overlap add method
The overlap add method is a technique used in digital signal processing to combine multiple blocks of signal data in the frequency domain. It is commonly used in applications such as convolution, filtering, and fast Fourier transform (FFT) computations.

Appending zeros
In the overlap add method, zeros are appended to each data block before performing the frequency domain operations. These zeros help to reduce spectral leakage and improve the accuracy of the computations.

Choice C: M-1 zeros are appended at the last of each data block
In the given options, choice C states that M-1 zeros are appended at the last of each data block. This means that M-1 zeros are added after the original data in each block.

Explanation
To understand why M-1 zeros are appended at the last of each data block in the overlap add method, let's break it down step by step:

1. Splitting the input signal: The original input signal is divided into multiple overlapping blocks of length M. Each block contains M samples.

2. Windowing: A window function is applied to each data block to reduce the spectral leakage phenomenon. The window function helps in tapering the edges of the block, reducing the abrupt transitions at the beginning and end.

3. Zero-padding: After applying the window function, M-1 zeros are appended at the last of each data block. This is done to avoid circular convolution artifacts and ensure that the frequency domain operations are performed properly.

4. FFT computation: Each windowed and zero-padded data block is then transformed into the frequency domain using the fast Fourier transform (FFT) algorithm. The FFT computes the discrete Fourier transform of the block, giving us the frequency representation of the signal.

5. Frequency domain operations: In the frequency domain, various operations such as multiplication, filtering, or convolution can be performed on the transformed blocks.

6. Inverse FFT: After the frequency domain operations, the inverse FFT is applied to each block to obtain the time-domain representation of the processed signal.

7. Overlap and add: Finally, the processed blocks are overlapped and added together to reconstruct the complete output signal.

By appending M-1 zeros at the last of each data block, the overlap add method ensures that the frequency domain operations are performed correctly and the output signal is accurately reconstructed.

Thus, the correct option is C) M-1 zeros are appended at the last of each data block.