Learning Experience: Overlap Add Method and Overlap Save Method

Experiment Performed and Conclusions Inferred:

We performed block processing using two methods, overlap add method and overlap save method. 

Overlap-Add method: In this method, the signal was decomposed into smaller signals depending upon the number of samples that allows circular convolution to be equivalent to linear convolution and zero padding was done prior to the FFT to prevent the wrapping around of values. Using Fast Fourier Transform method, linear convolution of the input signal was found. The output of the signals result into overlapping of the values for the same indexes, hence the final output consists of the addition of all of the overlapped outputs.

Overlap-Save Method: In overlap-save method the last part of the previous block is used as the first part of the next block. No zero padding is done of the data, hence the circular convolution is not equal to the linear convolution. The output of the convolution of different blocks are wrapped around. These portions are useless and they are simply discarded.  

While the computational time for OAS and OAM is the same, since OSM does not require the addition of the overlapped output, it is faster than OAM.