# Hop size in STFT

I am reading the documentation of scipy.signal.stft function: https://docs.scipy.org/doc/scipy/reference/generated/scipy.signal.stft.html#scipy.signal.stft. My question: is the 'noverlap' parameter of this function equivalent with STFT hop size?

• You might want to check out this answer for a reasonably complete description of STFT and how FFT size, overlap %, and Hop size are all related. Dec 2, 2021 at 5:32
• This answer might also be useful, if you're using a rectangular window and doing fast convolution. Dec 2, 2021 at 5:41

The hop size $$M$$ is the number of samples between each successive FFT. The 'noverlap' parameter is the number of samples $$n$$ to overlap between segments (and will default to $$N/2$$ where $$N$$ is the FFT frame size). The relationship between hop size, frame size and overlap is:

$$M$$ = $$N - n$$

If there is no overlap then this would simply be the total number of samples in the FFT frame. In certain uses the overlap is given as an "Overlap Factor", where a factor of 2 would refer to a 50% overlap (stated here in case that was a source of the OP's confusion; 'noverlap' is clearly stated in the documentation as the number of samples and does not represent "overlap factor").