Determining frequency content of a .wav file

Hi all,

The code I have written I think is correct. I am comparing two sound sources and not getting the desired outcome, one of the sound sources has a higher frequency content when it should be lower! I think there is something wrong with my Fourier Transform?

My code is as follows, any help would be much appreciated:

read in the .wav file

[y,fs]= audioread('CD152DEP1_20170829_160000.wav');
% y=samples
% fs=sampling frequency

Starttime=0;
Endtime=30;
time= Endtime-Starttime;
Sample=time.*fs;
Starty=Starttime.*fs
Endy=Endtime.*fs
t=linspace(Starttime,Endtime,Sample); 
%linspace function that creates evenly spaced time vector
y2=y((Starty+1):Endy,:);
figure;
subplot(3,1,1)
plot(t,y2);
xlabel('Time (seconds)') 
ylabel('Amplitude')
title('Day 1 Bolt 16.00') 
hold on 
%a is normalised into seconds for plot
%xlim([0 350])
%b= 45/350
%X = [b, b];
%Y = [0.8,0.5];
%a = annotation('textarrow',X,Y,'String','Lander crossing');

%%frequnecy analysis

Nfft=2048;
f=linspace(0,fs,Nfft); 
%f is freq vector, 0 starting freq, fs is end freq, Nfft is length of
%vector
G=abs(fft(y2,Nfft));
%G is the fft of y in the same number of points as the sample

%calculating the phase
phase = unwrap(angle(fft(y,Nfft)));
%subplot of phase and freq
subplot(3,1,2),plot((f(1:Nfft/2)),(G(1:Nfft/2)))
xlabel('Frequency(Hz)')  
ylabel('Amplitude')

xlim([0 1000])

hold on 
subplot(3,1,3), plot((f(1:Nfft/2)),(phase(1:Nfft/2)))
xlabel('Frequency(Hz)') 
ylabel('Phase(radians)')
xlim([0 1000])

[Star Strider]

You seem to be calculating the two-sided Fourier transform. That can be confusing to interpret.

See the documentation for fft (link) for the implementation you likely want.

[Image Analyst]

Try the pwelch() function and attach your two audio files if you need more help.

[Edward Jones]

Thank you for the responses, what would be the best approach to a extract the frequency content and plot it against the amplitude? I do not understand what you mean about it being two sided? I have tried pwelch but it does not seem to work for just plotting frequency vs amplitude?

The two files post audio read are attached

[Abhi Sundararaman]

I recommend walking through the example in our documentation for "fft", like Star Strider said. It will give you the process for plotting the fft in the way you expect:

https://www.mathworks.com/help/matlab/ref/fft.html#buuutyt-7