MATLAB: SYNTAX – obtain [pxx ,f] vectors from periodogram(_ fs); <— Errors in user's current usage

audio processingfigureMATLABnfftperiodogrampsdSignal Processing Toolboxsignalssyntaxwindow

QUESTION: How do I correctly use [pxx, f] = periodogram(y_soundsource_data,window,nfft, Fs);
I need the pxx and f vectors to be able to index to find maxima.
For context … trying to get the PSD local maxima, for 3 specific frequency ranges. I want both the x-frequency values and the PSD-y values.
(This was my trial yesterday which was very wrong —>https://dsp.stackexchange.com/questions/56468/normalizing-vectors-to-be-the-same-size-to-retain-psd-data)
I sent an email to someone, and he said to use the [pxx, f]= periodogram(_ Fs) version of the periodogram call.
Where pxx= the PSD y value vector and f= the x values which correspond to the frequency values that match 1:1 to the pxx points
Matlab Documentation Says:
matlabPeriodogram.JPG
Undesired Behavior:
  • When I do use [pxx, f] = periodogram(y_soundsource_data,window, nfft, Fs); a window maker pops up and it doesn't automatically plot or
calculate anything.
  • Tried function call–> [pxx, f]=periodogram([],Fs); which should give the PSD-estimate with default values, but then, it caused an error.
Code
    %% audioread .wav file
[y Fs]= audioread('100-daddy1.wav');
%% y=source signal
sourceFig=figure(1);
plot(y);
xlabel('milliseconds'); ylabel('amplitude'); title('spectrogram = voice source signal');
%% PSD - Power Spectral Density <-- peaks here should give formants
filterfcn=figure(2);
PSD=periodogram(y); %calculate the power spectral density of the source signal
plot(PSD);
ylabel('magnitude || intensity of signal'); xlabel('frequency in Hz'); title('PSD of Source');
xlim([0, .35*10^4]);
%% PSD with modified window <--- window is the same length as x
PSD_mod_window= periodogram(y, window);
figure(4);
plot(PSD_mod_window); % don't understand why a window pops up or how to use it. Thought window, was supposed to be a vector of length x?
%% [pxx,f] = periodogram(_,fs)
%fs is the fourth input to periodogram 
% to use default values, do [], for preceding args
[pxx4, f]= periodogram( [], Fs);
disp(sizeof(pxx4));
disp(sizeof(f));
How do I correctly use [pxx, f] = periodogram(y_soundsource_data,window,nfft, Fs); ?
I need the pxx and f vectors to be able to index to find maxima.

Best Answer

https://www.mathworks.com/help/signal/ref/periodogram.html
The reason window plotter came up, was because you used the window gate way function as an input argument to the call: [pxx, f] = periodogram(y_soundsource_data,window, nfft, Fs).
Deconstructing the [pxx, f]= periodogram(y_soundsource_data, window, nfft, Fs);
  1. You can get y_soundsource_data and Fs<-- sampling frequency, from the audioread function. file[y Fs]= audioread('100-daddy1.wav');
  2. window and nfft are not understood by the periodogram function UNLESS you define them.
  • y_soundsource_data and Fs are understood, because audioread returns the data metrics.
  • nfft - refers to the number of points used in the DFT. A larger nfft value will lead to a better estimation. nfft MUST be an integer. You can't have half a point.
  • window = vector of the size of the y_soundsource_data. 1:length_y_soundsource_data
  • both window and nfft need to be defined before you call the periodogram function.
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