Unit for linear power in line spectrum analysis

I am analysing a sound wave. I use audioread function of matlab for my analysis and plot my time series and frequency domain curves. When I use frequency domain I get linear and lograthmic plot. In lograthmic plot unit is "dB" I am confused what shoild be the unit in my linear plot. Should it be "V" or "Pa".

I want to know what units should I use here and what maths I should use to back it up, for my conversion from dB to linear scale.

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%===line spectrum

fSep=1/(N*h);

disp(['FFT frequency separation = ' num2str(fSep) ' Hz'])

[Y,f,YdB]=SimpleLineSpectrum2(y,h,0,fny);

figure

subplot(211)

plot(f,Y,'LineWidth',1.5),grid

title(['Line Spectrum of ' name ],'fontweight','bold','fontsize',10)

ylabel('Linear power') % "I want to know what UNIT should i use here"

xlabel('Frequency (Hz)')

axis([fL fR 0 max(Y)])

subplot(212)

plot(f,YdB,'LineWidth',1.5),grid

title('Line Spectrum in dB','fontweight','bold')

ylabel('power (dB)')

xlabel('frequency (Hz)')

axis([fL fR dBmin 0])

pause

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