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How to make the x-axis on a logarithmic scale while keeping the y-axis in dB?

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gaurav Nanda
gaurav Nanda 2012-4-25
Hello,
I have calculated the PSD of my signal in dB.
lets say,
f=frequency
Nc= (PSD)Power spectral density in dB
plot(f,Nc);
Now, I would like to change the x-axis to logarithmic scale while keeping the y-axis in dB and plot it. Could you please tell me how to do that?
Thanks
Gaurav

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采纳的回答

Wayne King
Wayne King 2012-4-25
semilogx(f,10*log10(Nc))

更多回答（2 个）

Sean de Wolski
Sean de Wolski 2012-4-25
Wayne's method is probably best. However, if you need finer control you can set the axes' xscale property to log.
h = axes;
set(h,'xscale','log')
gaurav Nanda
gaurav Nanda 2012-4-25
Thanks for the help.
I also need to perform curve fitting and to find the value of (C)
This is how I am doing it
g = fittype('a+b./(f.^c)',... 'independent', 'f',... 'coefficients', {'a','b','c'});
f1 = fit(f, Nc, g)
where a= thermal noise
b/f^c is pink noise
I have defined the fittype but I am not able to find the value of c.

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