How can I smooth out my spectral phase plot in Matlab?

In summary, spectral phase in Matlab refers to the variation in the phase of a signal as a function of frequency. To plot spectral phase, the <code>angle()</code> and <code>plot()</code> functions can be used. It is possible to plot the spectral phase of a specific signal by selecting the signal and applying the appropriate functions. The spectral phase plot in Matlab can be interpreted by looking at the linearity and slope, which indicate the amount of phase change over a given frequency range. Other tools in Matlab for analyzing spectral phase include the <code>unwrap()</code> and <code>hilbert()</code> functions.
  • #1
snatcos
4
0
Hi everyone,

I have this Matlab code :

function PH = testing
close all;
x = [0:1e-3:10-1e-3];
ph = -(x-5).^2;
y = exp(-(x-5).^2./(0.2^2)).*exp(i*2*pi*ph);

Y = fft(y);
Y = fftshift(Y);
PH = angle(Y);
X = (x(2) - x(1))^-1*linspace(0,1,length(x));

figure
plot(x,ph);
figure
plot(X,PH);
end

I build a gaussian curve with quadratic phase and Fourier Transform it. I expect to have a quadratic phase (with opposite sign) in the spectral domain, but I cannot have it correctly. The plot of PH shows jumps between adjacent points. Even using unwrap.m I cannot plot it well.

Thanks in advance for any help
 
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  • #2
.</code>It seems like the problem is caused by the finite length of the time domain signal. To solve this issue, you can try zero-padding your signal before taking the FFT. This will increase the frequency resolution and should help to reduce the jumps in the phase plot. For example, you can add zeros to the end of your x array with the following command:x = [x, zeros(1,length(x))];Then take the FFT of the new array. This should produce a smoother phase plot.Hope this helps!
 

1. What is spectral phase in Matlab?

Spectral phase in Matlab refers to the variation in the phase of a signal as a function of frequency. It is commonly used in signal processing and communication applications to analyze and manipulate the spectral content of a signal.

2. How can I plot spectral phase in Matlab?

To plot spectral phase in Matlab, you can use the angle() function to calculate the phase of the signal and then use the plot() function to graph the phase against frequency.

3. Can I plot the spectral phase of a specific signal in Matlab?

Yes, you can plot the spectral phase of a specific signal in Matlab by first selecting the signal using the appropriate indexing method, and then applying the angle() and plot() functions to the selected signal.

4. How can I interpret the spectral phase plot in Matlab?

The spectral phase plot in Matlab shows the phase of the signal at different frequencies. A flat line indicates that the signal has a constant phase across all frequencies, while a non-linear plot indicates a varying phase. The slope of the plot also indicates the amount of phase change over a given frequency range.

5. Are there any other tools in Matlab for analyzing spectral phase?

Yes, Matlab also offers the unwrap() function, which can be used to remove any discontinuities in the spectral phase plot. Additionally, the hilbert() function can be used to calculate the analytic signal, which can then be used to obtain the instantaneous phase and group delay of a signal.

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