Understanding the Spectrogram function

The y- axis of the spectrogram plot shows normalized frequencies that go up to 1, but the 's' matrix that stores the spectrogram properties has values that go up to 3000. Why is that?

Answer 1

[Priyank Sharma]

The output 's' of the functioni is the Short-time Fourier transform which is returned as a matrix.

In the matrix, time increases across the columns of s and frequency increases down the rows, starting from zero.

If x is a signal of length Nx, then s has k columns, where

• k = ⌊(Nx – noverlap)/(window – noverlap)⌋ if window is a scalar.
• k = ⌊(Nx – noverlap)/(length(window) – noverlap)⌋ if window is a vector.