Units of spectrogram and pspectrum questions

Hi

I have a time signal as follows:

I am trying out "pspectrum" and "spectrogram" to see this signal in frequency-time domain and frequency domain.

The left picture is the result of "pspectrum" and at the right "spectrogram". Now i have some questions regarding the units of the amplitude. With "pspectrum" the unit is expressed as db and with "spectrogram" the unit is expressed as db/Hz. What is the difference between these two units?

My second question and also the most important one is as follows: I need to extract the signal information from these figures, so im using the output arguments with these two. For both functions you get a mxn matrix but both has other values. i want to know what the units are from these two, how can i calculate amplitude in "volts" from these values? The matrix at the top is the result of "pspectrum" and the bottom matrix is the result of "spectrogram". With spectrogram i know i need to use abs(x) to get the amplitude information.

Summarized: i want to know what the units of these two output arguments are and how can i transform them to a unit expressed in "volt"?

PS: the time domain is a sinus with a frequency of 50Hz. The top matrix show the values corresponding with the frequency 50Hz wich is 0.0032. for the bottom matrix row #80 corresponds with 50Hz)

any help would be appreciated!

With kind regards

Answer 1

[Frantz Bouchereau]

spectrogram by default plots the magnitude of the power spectral density and hence the units at db/Hz. pspectrum computes and plots power spectrum so the units are simply dB.

pspectrum outputs short-time power spectrum columns in linear units (Watts with respect to a 1 Ohm load).

HTH