Matab Spectrogram Colour Axis

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Ajay 2012-3-27

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Hello,

I am trying to perform audio analysis with Matlab s spectrogram. I tried with 50 msec Hamming window and 50 % overlap. on some mp3 and wav files sampled at 44 kHz. I am getting a very sparse plot in the spectrogram (ie most of the colour area is blueish) and only if I focus down to the lower most frequencies ( less than 500 Hz) I am able to see something.

So this could be due to color scaling but why is the spectrogram displayed by Matlab have such low values of amplitude at higher frequencies ? How do I set an appropriate colour range for the plot ? Because I intend to use spectrograms for my work , I would like to know if they are supposed to apear this way or not.

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Answer 1

Daniel Shub 2012-3-27

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It is probably not a color range issue. Rather, it sounds like your audio signal has a "pink" (1/f) spectrum where there is more power, for a given bandwidth at low frequencies than at high frequencies. You could smooth the spectrogram with a filter that changes bandwidth with frequency (think log/octave bin widths), but this is a pain.

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Ajay 2012-3-27

I plan to use this Spectrogram for feature extraction from audio for comparing audio similarity, so I would like to know whether waht you have suggested is needed or not. Also , whether the Spectrogram is a decent tool or I need to look at higher features like Ceptsral Coefficiets etc. and for that whether I could use these Spectrogram.

Daniel Shub 2012-3-27

Presumably you are not going to extract the features from the visual representation, so the color axis should not matter. As for what is the right domain to look for features in, there is a whole literature on that.

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