How to get the phase angle for an extracted fft plot?

Goodnight,

Basically I had a signal and ran the fft command, which I then extracted a specific section of the fft plot. Now for that section I'll like to find the associated phase angle. Below is my code.

 %%Import the mp3 file

[y,Fs] = audioread('Voice010.mp3');

%% Calculate size of the imported data

nfft = length(y);% length of the fft x=fft(y,nfft); mx=abs(x);%Absolute value f=Fs*(0:(nfft-1))/nfft;% Convert Time to the Frequency Domain mp3data = [f' mx];

%% Graph Displaying entire signal #1

figure(1); plot(f,mx,'-m','linewidth',0.25); xlim([80 500]); grid on; xlabel('Frequency,(Hz)'); ylabel('Amplitude,(Dimensionless)'); title('Sound Sample');

%% Extracting Data

mx_prime = mx>1000;

%% This matrix below contains all values for the amplitude greater than 1000

mx_1000 = mp3data(mx_prime,:);

%% Set the x limits

f_prime = (mx_1000(:,1)>80 & mx_1000(:,1)<250);

%% Combine the extracted data

mp3data_extracted = mx_1000(f_prime,:);

%% Graph displaying the extracted data #2

figure(2); hold on; plot(f,mx,'-m','linewidth',0.25); hold on; plot(mp3data_extracted(:,1),mp3data_extracted(:,2),'-b','linewidth',0.25); legend('Initial Data','Extracted data'); xlim([80 500]); grid on; xlabel('Frequency,(Hz)'); ylabel('Amplitude (Dimensionless)'); title('Sound Sample');

%% Graph 3 displaying the phase angle p=unwrap(angle(x)); figure(3); hold on; plot(f,p); xlim([80 500]); grid on; xlabel('Frequency,(Hz)'); ylabel('Phase / \pi'); title('Sound Sample');

Answer 1

[Star Strider]

‘I'll like to find the associated phase angle’

It seems to me you did that here:

p=unwrap(angle(x));

If you take the Fourier transform of the entire signal, there is no way for you to identify afterwards what a part of the signal contributed to the entire Fourier transform. You have to use the spectrogram function to get a time-frequency analysis. I have not attempted to get phase information from the spectrogram output, so I leave it to you to experiment with that.