How to draw a high-contrast spectrogram?

Some software for sound analysis can draw spectrograms with higher contrast (backgrounds are almost zero). I was wondering what tricks may I use to generate similar spectrograms.

Figure-1 A spectrogram generated by matlab function spectrogram()

Figure-2 A spectrogram of the same audio signal generated by a software

Answer 1

[Sulaymon Eshkabilov]

Hi,

Use colormap()

[zhehao.nkd]

Hi, thank you very much! Could you please tell me more about the details, do you mean self-defining the colormap values?

[Sulaymon Eshkabilov]

colormap(jet); colormat(hsv); etc

[zhehao.nkd]

Thank you for your reply! But I am sorry that the way I ask my question may be misleading. Increasing the contrast by applying different colormaps may not be what I need. Instead, I would like to improve the contrast by cleaning the noisy background as the second Figure shows. Is there any possible solution?

Answer 2

[Andres Morales]

You can modify the spectrogram minimum thresholding value. This will zero values below the threshold:

https://www.mathworks.com/help/signal/ref/spectrogram.html#namevaluepairarguments