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

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

Answer 1

[Wayne King]

   semilogx(f,10*log10(Nc))

Answer 2

[Sean de Wolski]

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')

Answer 3

[gaurav Nanda]

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.