Manual STFT to obtain spectrogram of an audio signal

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Fernanda Cortes
Fernanda Cortes 2019-6-14
回答： UMAIR RASOOL 2020-8-1
Hi, Im trying to obtain the notes that are on an audio signal by using the spectrogram to know the frequencies on it, but i dont know why this code plots me an empty graph. Can sombody help me please.
[x,fs]= audioread("estrellita.mp3");
dt = 1/44100;
t=0:dt:(117204*dt)-dt;
S = zeros(501,117);
windowlength = 1e3;
k = 1;
for jj = 1:117
y = x(k:k+windowlength-1)';
ydft = fft(y).*gausswin(1e3);
S(:,jj) = ydft(1:501);
k = k+windowlength;
end
F = 0:44100/1000:44100/2;
T = 0:(1e3*dt):(117000*dt)-(1e3*dt);
surf(T,F,20*log10(abs(S)),'EdgeColor','none')
axis xy; axis tight; colormap(jet); view(0,90);
xlabel('Time');
ylabel('Frequency (Hz)');
set(gca,'YDir','Normal')
xlabel('Time (secs)')
ylabel('Freq (Hz)')
title('Short-time Fourier Transform spectrum')

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回答（1 个）

UMAIR RASOOL
UMAIR RASOOL 2020-8-1
close all
clear all
clc
[y,Fs]=audioread('black_hole.mp3');
Y=fft(y,Fs);
L= (1:length(Y))*Fs/length(Y);
plot(L,abs(Y))
xlabel('Frequency');
ylabel('Amplitude');
title('(Magnitude Spectrum')
windowSize = 256;
windowOverlap = [];
freqRange = 0:Fs;
spectrogram(y(:,1), windowSize, windowOverlap, freqRange, Fs, 'xaxis');

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