Cutting of unused frequencies in specgram matplotlib

Question

I have a signal with sampling rate 16e3, its frequency range is from 125 to 1000 Hz. So if i plot a specgram i get a pretty small colorrange because of all the unused frequencys

Answer 1

These days, there's an easier way to do this than when the question was asked: you can use matplotlib.pyplot.axis to set ymin and ymax to your desired frequencies. It's quite easy; here's a snippet from my program:

plt.specgram(xmit, NFFT=65536, Fs=Fs)
plt.axis(ymin=Fc-Fa*10, ymax=Fc+Fa*10)
plt.show()