phaseplot(f,op1,op2, ... ); phaseplot(f,fs,op1,op2, ... );
phaseplot(f) plots the phase of f using a dgt.
phaseplot(f,fs) does the same for a signal with sampling rate fs Hz.
phaseplot should only be used for short signals (shorter than the resolution of the screen), as there will otherwise be some visual aliasing, such that very fast changing areas will look very smooth. phaseplot always calculates the phase of the full time/frequency plane (as opposed to sgram), and you therefore risk running out of memory for long signals.
phaseplot takes the following flags at the end of the line of input arguments:
| 'tfr',v | Set the ratio of frequency resolution to time resolution. A value \(v=1\) is the default. Setting \(v>1\) will give better frequency resolution at the expense of a worse time resolution. A value of \(0<v<1\) will do the opposite. |
| 'wlen',s | Window length. Specifies the length of the window measured in samples. See help of pgauss on the exact details of the window length. |
| 'nf' | Display negative frequencies, with the zero-frequency centered in the middle. For real signals, this will just mirror the upper half plane. This is standard for complex signals. |
| 'tc' | Time centering. Move the beginning of the signal to the middle of the plot. This is usefull for visualizing the window functions of the toolbox. |
| 'thr',r | Keep the coefficients with a magnitude larger than r times the largest magnitude. Set the phase of the rest of the coefficients to zero. This is useful, because for small amplitude the phase values can be meaningless. |
| 'timeinv' | Display the phase as computed by a time-invariant dgt. This is the default. |
| 'freqinv' | Display the phase as computed by a frequency-invariant dgt. |
| 'fmax',y | Display y as the highest frequency. |
| 'colorbar' | Display the colorbar. This is the default. |
| 'nocolorbar' | Do not display the colorbar. |
For the best result when using phaseplot, use a circulant color map, for instance hsv.
The following code shows the phaseplot of a periodic, hyperbolic secant visualized using the hsv colormap:
phaseplot(psech(200),'tc','nf'); colormap(hsv);
The following phaseplot shows the phase of white, Gaussian noise:
phaseplot(randn(200,1)); colormap(hsv);
R. Carmona, W. Hwang, and B. Torrésani. Practical Time-Frequency Analysis: continuous wavelet and Gabor transforms, with an implementation in S, volume 9 of Wavelet Analysis and its Applications. Academic Press, San Diego, 1998.