![]() absolute value of STFT (amplitude), then loss of this information is fairly minimal: taking absolute value globally shifts frequencies of every row toward low frequencies, and most often very low frequencies, which permits a generous hop length. The good news is, if all you seek is the spectrogram, i.e. The lesser the overlap (greater hop length), the less dynamics are captured. For STFT, it refers to time-frequency modulation information: a row captures (within the window's resolution) the instantaneous frequency and amplitude of the signal over time. "Analysis information" is the very goal of transforming data in the first place (if all we cared for was preserving the input, simply don't do a transform). If hop length is 4, then 0.125 to 0.5 is aliased, and so on. Namely, from 0 to 0.5 times the sampling frequency, if "hop length" is 2, then analysis information for frequencies bewteen 0.25 and 0.5 is aliased. If there is overlap, but it is little, then analysis information is lost (but not synthesis, which is more fundamental). If there no overlap, then invertibility is lost, and so is information. Due to not overlapping you are "missing" the main event in the signal as it falls "between windows".ĥ0% overlap fixes this, since the n=128 is right in the center of the next overlapping window. If your input is a unit impulse at n = 128, you are at the very last sample of the first window, the weight here is tiny (0.00059297) and so your spectrum is down by more than -64 dB which is clearly wrong. If your input is a unit impulse at n = 64 you are in the middle of the first window, the weight is one and you get a flat spectrum at 0 dB. Let's say you have non-overlapping Hanning windows of length 128 centered around n = 64, 192, 320, etc. This depends very much on the signal, but here is an example. What will happen if I don't overlap the successive windows? ![]() ![]() How to calculate the number of points that need to be overlapped?įor many "normal" windows (hanning, hamming, etc.) 50% overlap works fine for most applications. This is can be conveniently done by overlapping the windows. Hence a sample at the edge must be weighted higher in the next (or previous) window. Any window weighs the samples in the middle higher than the one at the edges. Overlap is needed to make sure all samples are weighed equally (at least roughly).In order to reduce spectral leakage the window must fade out at the ends of the window.If you don't know what this is, just search this forum or ask a separate question. The main purpose of windowing is to manage the amount of spectral leakage.
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