Frequency spectrum of a sound signal

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Lok Hua Lee
Lok Hua Lee on 20 Oct 2019
Commented: Keira Duffy on 20 Sep 2021
Hi guys, I would like to know some hints on how to plot frequency spectrum of magnitude and phase spectra of an audio signal in both omega and frequency as x-axis parameter (plot separately). Thanks. My code is as below and i'm not sure what's going on.
[y,fs] = audioread('test.wave');
N = length(y);
t = (0:N-1/fs);
n = (0:N-1);
y = y(:,1);
% spectral analysis
w = hanning(N, 'periodic');
[X, f] = periodogram(y, w, N, fs, 'power');
X = 20*log10(sqrt(X)*sqrt(2));
% plot the signal spectrum
figure(1);
subplot(2,1,1);
semilogx(f, X, 'r');
xlim([0 max(f)]);
grid on;
set(gca, 'FontName', 'Times New Roman', 'FontSize', 14);
title('Amplitude spectrum of the signal');
xlabel('Frequency, Cycles/Second');
ylabel('Magnitude, dB');
subplot(2,1,2);
semilogx((2*pi*f), X, 'r');
xlim([0 max(2*pi*f)]);
grid on;
set(gca, 'FontName', 'Times New Roman', 'FontSize', 14);
title('Amplitude spectrum of the signal');
xlabel('Angular Frequency, Radian/Sample');
ylabel('Magnitude, dB');

Answers (1)

Kaashyap Pappu
Kaashyap Pappu on 23 Oct 2019
Using a test sound file of my own, I was able to generate the plots attached. The function “audioread” works if the suffix of the sound file name is ‘.wav’ not ‘.wave’.
A similar question has been addressed here.
Hope this helps!
  2 Comments
Keira Duffy
Keira Duffy on 20 Sep 2021
When you do magnitudeY = abs(Y); you automatically assumed that it is in decibels but it is not. Dont you need to take the log10 to convert it?

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