How can I plot some fft data in a different way?

2021 7 21
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更新时间：2021 7 22
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Dear all,
I usual plot spectrograms plotting time vs. frequency vs. amplitude. I have collected some records through a microphone and each of the recordings are named usign a parameter, so called 'ϕ'. I would like to plot a single spectrogram similar to the one in the attached picture containing my data. File structure is 2 colums (time and amplitude) and 10000 rows.
Could you please help me making this "ϕ vs. frequency vs. amplitude" plot by using the two signal files attached?
I would sincerly appreciate it since I am litterally freaking out trying to fixing this issue.

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Yazan
Yazan 2021-7-21
Define for us first the relation between time and ϕ. As you said, the spectrogram helps you plot the instantaneous spectra. To plot the instantaneous spectra as a function of ϕ, you need to define the relation between ϕ and time.
Well, there's not a mathematical or physical relation between time and ϕ. The latter is just a parameter useful for me to recognize the differences between the two cases.
Probably I didn't explain myself in the best way: I would like to plot the spectrogram of my two signal close to each other but I would like to plot values of ϕalong the x-axis (similarly to the attached picture).
Yazan
Yazan 2021-7-22
编辑：Yazan 2021-7-22
Where are the values of ϕ? In the txt files, I can see time and amplitude. Also, what do you mean by close to each others? on the same axes (appending the first signal with the second?)? Or two subplots?
Francesco Pignatelli
编辑：Francesco Pignatelli 2021-7-22
Values of ϕ are in the file name: 0.66 and 0.68,respectively.
When I say close to each other I mean attached/stitched. I attach an example regarding what I would like to have.

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Yazan
Yazan 2021-7-22
编辑：Yazan 2021-7-22

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The first column in the txt files you provided is a DateTime vector, so again, I am not able to understand how ϕ is defined. I will assume that the seconds in the DateTime vector represent ϕ.
clc, clear, close all
% read data
opts = detectImportOptions('CH4_NO_PILOT_RE_10K_PHI_066.txt');
opts.VariableNames = {'Time', 'Amp'};
opts.DataLines = [5 inf];
ch1 = readtable('CH4_NO_PILOT_RE_10K_PHI_066.txt', opts);
ch2 = readtable('CH4_NO_PILOT_RE_10K_PHI_068.txt', opts);
% get the time instants at which the signal is sampled
ch1.Time = seconds(ch1.Time - ch1.Time(1));
ch2.Time = seconds(ch2.Time - ch2.Time(1));
% sampling period
Ts = ch1.Time(2) - ch1.Time(1);
% downsample by a factor of 5 to reduce the number of datapoints
% this part can be skipped
sig1 = resample(ch1.Amp, 1, 5);
sig2 = resample(ch2.Amp, 1, 5);
Ts = Ts*5;
% histogram computation
[sp1, f, t] = pspectrum(sig1, 1/Ts, 'spectrogram', 'OverlapPercent', 25, 'Leakage', 0.8);
sp2 = pspectrum(sig2, 1/Ts, 'spectrogram', 'OverlapPercent', 25, 'Leakage', 0.8);
% append the second histogram with the first
spTot = pow2db([sp1, sp2]); t = [t; t]; Nt = length(t)/2;
% plot
figure,
ax = axes(gcf);
imagesc(1:2*Nt, f./1000, spTot);
cb = colorbar; axis xy
% label the x-axis as phi (usually it should be time)
xlabel('\phi', 'FontSize', 15),
% label the other axes
ylabel('Frequency (KHz)', 'FontSize', 15)
cb.Label.String = 'Power (dB)';
% change the x-axis ticks
ax.XTick = Nt*(0.5:0.5:2);
ax.XTickLabel = arrayfun(@(x) num2str(x), t(ax.XTick), 'UniformOutput', false);
% vertical line to separate the two histograms
xline(Nt, 'LineWidth', 3, 'LineStyle', '--', 'Color', 'r')
% annotate the figure
annotation('textbox', 'Position', [0.18,0.8,0.22,0.1], 'String', 'Histogram 1',...
'FontSize', 15)
annotation('textbox', 'Position', [0.5,0.8,0.22,0.1], 'String', 'Histogram 2',...
'FontSize', 15)

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I have tested your code and it seems working regularly out of the following two lines:
[sp1, f, t] = pspectrum(sig1, 1/Ts, 'spectrogram', 'OverlapPercent', 25, 'Leakage', 0.8);
sp2 = pspectrum(sig2, 1/Ts, 'spectrogram', 'OverlapPercent', 25, 'Leakage', 0.8);
since my Matlab complains with the following error message:
"The denominator in matrix division for duration arrays must be a real scalar double value."
that I have fixed just by not using Ts as duration but as a value.
The latest thing regarding ϕ: what I want is something similar to the following:
So that it is possible to distinguish the first dataset from the second one.
Yazan
Yazan 2021-7-22
Use the following
% change the x-axis ticks
ax.XTick = Nt*([0.5 1.5]);
ax.XTickLabel = [{'\phi = 0.66'}, {'\phi = 0.68'}];
Now it is perfect! Thank you very much for your help Yazan, I really appreciate it :)
I hope to "meet" you again in this MATLAB comunity. Bye :)

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Chunru
Chunru 2021-7-22
Ran in:

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Ran in:
% Assume there are 3 spec (corresponding to phi)
nf = 20; nt=15; nspec = 3;
sp = randn(nf, nt, nspec);
% reshape the spectrogram to 2D
sp = reshape(sp, [nf, nt*nspec]);
% multiple spectrograms
imagesc(sp);
% annotation
h = gca;
h.XTick = 0.5+(0:nspec-1)*nt;
h.YTick = [];
grid on
phi = [1.2 3.4 5.6];
h.XTickLabel = string(phi);
xlabel('\phi')

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Hello Chunru, thank you very much for your efforts, I really appreciate it :)

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