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Please, I have a recorded audio signal from experimental work. I have been able to plot the time domain graph (see attached) using Matlab software. By default, the y-axis values are present in a linear scale (Amplitude). I would like to plot the time domain graph such that the y-axis scale is is in decibel. I understand that using 20*log10(signal/ref. signal) should provide the decibel scale on the y-axis, however, this does not seem to work after several attempts.

** My code**

Let say the signa name is TD, so I use the code plot(20*log10(TD/20*10^-6)), the 20*10^-6 is my reference air pressure. The problem is that the entire signal is distorted.

Please, I would be glad if someone can assist me (specifically with a code in matlab to visualise the signal). I might not be doing something right. Thank you.

Thank you.

dpb
on 15 Jan 2021

Edited: dpb
on 15 Jan 2021

See the attached link https://www.dsprelated.com/freebooks/mdft/Decibels.html

In particular, note that "Signal intensity, power, and energy are always proportional to the square of the signal amplitude.power". When you just use a zero-mean time trace, the log10 is undefined for values <=0 which is what is happening with what you've tried so far.

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