How do I present an audio signal in a time domain plot using MATLAB, such that the y-axis is in decibel (dB) instead of of a linear scale?

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.

[Cris LaPierre]

Share what you have so we can help you fix your code. What error are you getting? What is wrong about the values you are getting when you convert your y values to dB?

[Kwaku Owusu]

Please, I have attached the signal for observation. 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.

[dpb]

"I have attached the signal..."

Nothing was attached.

[Kwaku Owusu]

Sorry, it's now attached. Thank you.

[Mathieu NOE]

hello

do not forget to take the abs of your time data before doing the 20*log10 action

spl = 20*log10(abs(TD/20*10^-6))

maybe some smoothing may be needed (=> movmean)

make sure that TD signal unit is Pascals

[Kwaku Owusu]

Thank you very much, Mathieu.

Answer 1

[dpb]

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.

[Kwaku Owusu]

Thank you