short time fourier transform (STFT) frequency axis

[JBarney]

Could someone please explain the frequency axis output of the short-time fourier transform spectrogram? The help menu indicates that the number of output columns will be equal to (# of input samples)/2. I would expect that the number of output frequency bins would be equal to half the size of the fft and that the bin width would be determined by the sample rate.

[Xy]

STFT is implemented using the windowed Fourier transform. Before applying the Fourier transform, the windowed signal can be zero-padded to get the same length as the input signal. So in this case, the FFT length is equal to the signal length. Such zero padding can get a smooth spectrogram for the detailed visual investigation of frequency contents.

NISH DSP

[JuanCarlos]

If you want to process large ammounts of data it would be a good idea to cut it in subsets. This would reduce the number of points passed to the STFT vi creating smaller FFTs. This in part would reduce the processing time.

Just my 2 cents.

Juan Carlos
N.I.

[Xy]

For the large data set, the JTFA functions in Advanced Signal Processing Toolset 7.0 are the better choices. In these functions, the frequency bins are determined by the "num of freq bins" setting.