# How does the size of a spectrogram relate to window length and frame rate?

I'm trying to understand the methodology from section 4 in this report about audio classification but I have some trouble understanding how they pre-process the data (dsp is not my area).

• $$30$$ seconds audio clips are available, sampled at $$22050\textrm{ samples/s}$$.
• The STFT is computed "on $$2048$$ sample windows at a frame rate of $$31.25\textrm{ frames/s}$$"

Somehow this results in spectrograms of size $$149\times 149$$ which are then feeded to a neural network.

• Does each spectrogram cover $$2048$$ samples of the audio clip?

• If so, is then $$149$$ the number of segments that we divide each spectrogram in?

• So that $$2048/149 = 13.745$$ is the number of samples that we use for computing the DFT in each segment? How can this be a non-integer?

To my understanding the frame rate is about how much overlap there are between windows, in this case the overlap would be $$22050/31.25 = 705.6 \textrm{ samples}$$, is that correct? How can this be a non-integer?

• "a report": which report? Cite! We can only guess from the numbers you're giving. Also, not all papers fully describe what they're doing, so this might simply be a case of "sorry, we don't know what the authors did, either". – Marcus Müller Apr 20 '17 at 9:55
• Ok, added a link. But i think i gave all the relevant information. – termachine Apr 20 '17 at 10:12