FFT overlap for feature extraction – DSP and Plugin Development Forum

FFT is periodic, so usually you’d usually apply a window function to suppress discontinuity at the “wrap-around” point (=frame boundary). When you’re reconstructing with IFFT, you’d then do overlap so that you can arrange windows from adjacent frames to add together to unity to avoid gain modulation. This doesn’t fully solve other issues that periodicity can cause, but at least it helps suppress the most obvious ones. The case of overlap with fast-convolution is a bit different, because there we arrange frame artifacts to cancel out exactly, but again the overlapping is there to deal with something specific.

If you’re doing pure analysis, you generally still want a window, but if we’re not going to be doing IFFT then the time offset from one frame to another is effectively a free parameter. If you skip data, then there’s the possibility you miss something important, if you overlap the data you get results that vary smoother from frame to frame and there’s less chance that something important never aligns with the part of the frame where the window function is large… but there’s nothing special about overlap here, we’re just looking at the signal at more points in time, so the question is basically “what is good enough for you?”