How do I plot a phase plot for FFT and code time history for down-sampled signal?
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Hello,
Thus far, i have completed this code which gave me a frequency vs amplitude graph. I'm ussure how to get a phase graph from this or time history of down sampled signal by a given rate etc I nwould be grateful for assistance for this.
data = [0 0.829668000000000
0.00833300000000000 0.829801000000000
0.0166670000000000 0.828810000000000
0.0250000000000000 0.829008000000000
0.0333330000000000 0.828352000000000
0.0416670000000000 0.827073000000000
0.0500000000000000 0.826807000000000
0.0583330000000000 0.826828000000000
0.0666670000000000 0.826857000000000
0.0750000000000000 0.827056000000000
0.0833330000000000 0.827139000000000
0.0916670000000000 0.828689000000000]
t = data(:,1);
s = data(:,2);
Ts= 0.0083;
Fs=1/Ts;
Fn= Fs/2;
L=4000;
smean=mean(s);
Fts=fft(s-smean)/L;
Fv= linspace(0,1,fix(L/2)+1)*Fn;
Iv=1:numel(Fv);
figure
plot(Fv,abs(Fts(Iv))*2)
grid
xlabel('frequency')
ylabel('Amplitude')
采纳的回答
Perhaps this —
data = [0 0.829668000000000
0.00833300000000000 0.829801000000000
0.0166670000000000 0.828810000000000
0.0250000000000000 0.829008000000000
0.0333330000000000 0.828352000000000
0.0416670000000000 0.827073000000000
0.0500000000000000 0.826807000000000
0.0583330000000000 0.826828000000000
0.0666670000000000 0.826857000000000
0.0750000000000000 0.827056000000000
0.0833330000000000 0.827139000000000
0.0916670000000000 0.828689000000000]
t = data(:,1);
s = data(:,2);
Ts= 0.0083;
Fs=1/Ts;
Fn= Fs/2;
L=size(data,1);
smean=mean(s);
NFFT = 2^nextpow2(L);
FTs=fft((s-smean).*hann(L))/L;
Fv= linspace(0,1,NFFT/2+1)*Fn;
Iv=1:numel(Fv);
figure
subplot(2,1,1)
plot(Fv,abs(FTs(Iv))*2)
grid
ylabel('Amplitude')
subplot(2,1,2)
plot(Fv,rad2deg(angle(FTs(Iv))))
grid
xlabel('Frequency')
ylabel('Phase (°)')
Also consider using unwrap for the radian phase, as: ‘rad2deg(unwrap(angle(FTs(Iv))))’. (I made a few improvements in my original code.)
.
4 个评论
omar ali
2023-5-7
Star Strider
2023-5-7
I am not certain what you mean by ‘time history’. That is generally shown by plotting the signal as a function of time, that being a time-domain plot.
If you want the frequency as a function of time, use the pspectrum function with the 'spectrogram' option. (I prefer pspectrum to spectrogram because the units are easier to interpret.)
The pspectrum function does not display phase. I have never displayed a phase plot as a function of time, although that could be possible by creating a matrix consisting of phase calculation vectors over different time windows corresponding to the pspectrum time windows, and then using surf to plot the resulting matrix. They would have to be displayed on different axes.
omar ali
2023-5-8
Star Strider
2023-5-8
As always, my pleasure!
I would do this instead —
F = 8
Fs = 30
[y, x] = butter(5, F/(Fs/2), 'low’)
inputSignal = s;
outSignal = filtfilt(y, x, inputSignal);
figure
plot(t, outSignal)
There is no reason to include the time vector in the signal being filtered, so I eliminated it here.
However if you want to concatenate two column vectors, use square brackets as [a, b] (although the comma is optional) and if you want to concatenate two row vectors [a; b] using the semicolon to create a second row (to vertically concatenate them). In all instances, the vectos must have the same row and column dimensions.
Actually, I would design the filter differently (I prefer elliptic filters because they are more computationally efficient), however to design a Butterworth filter I would begin with the buttord function, then butter, however producing zero-pole-gain output, and then use the zp2sos function to produce a second-order-section representation, and call filtfilt as:
outSignal = filtfilt(sos, g, inputSignal);
The filtering will be more effective and the filter will always be stable with these changes.
.
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