Can I adjust spectogram frequency axes?
The MATLAB documentation examples for the spectrogram function gives examples that have the frequency axis set to [0 500]. Can I change this to something like [0 100]? Obviously running the axis command will do this for me, but that adjusts the end result and "blows up" the resultant plot, make it pixelated. I am basically looking to build a spectrogram that only looks for frequencies between 0-100, not rescaling after building the spectrogram.
Here's an example from that documentation:
T = 0:0.001:2;
X = chirp(T,0,1,150);
spectrogram(X,256,250,256,1E3,'yaxis');
This produces the following:
Everything below 350Hz is unneeded. Is there a way to not include everything between 350 to 500 when building the spectrogram, rather than adjusting axes after the fact?
Answer
From the documentation:
[S,F,T] = spectrogram(x,window,noverlap,F) uses a vector F of frequencies in Hz. F must be a vector with at least two elements. This case computes the spectrogram at the frequencies in F using the Goertzel algorithm. The specified frequencies are rounded to the nearest DFT bin commensurate with the signal's resolution. In all other syntax cases where nfft or a default for nfft is used, the short-time Fourier transform is used. The F vector returned is a vector of the rounded frequencies. T is a vector of times at which the spectrogram is computed. The length of F is equal to the number of rows of S. The length of T is equal to k, as defined above and each value corresponds to the center of each segment.
Does that help you?