Como fazer gráfico de frequência fft

Good Morning! I'm trying to plot the fft graph, but I have to set the frequency, but I'm not getting it.

close all

clear all

clc;

load('testmarcio.mat');

x = dados;

M = length (x); % comprimento do sinal

p = (1-0.67); % sobreposição

% Divisão de blocos

n = 5; % número de blocos

N = fix (M/(1 + (n-1)*p)); % comprimento do bloco

m1 = 1;

m2 = N;

z2 = 0;

for v = 1:n

x1 = x(m1:m2); % um pedaço

Z1 = fft(x1); %transformada de Fourier

z2 = z2 + conj(Z1); %conjugado de z1

m1 = m1 + fix(p*N); % inicio

m2 = m1 + N-1; %final

end

% Módulo da Transformada de Fourier

z = abs(z2);

plot(abs(z2));

%title('Espectro do sinal(Domínio da frequência)')

%ylabel('Amplitude');

%xlabel('Frequência (Hz)');

Answer 1

[Mathieu NOE]

hello

we cannot test your code as you don't provide the mat file (use the paperclip button)

otherwise I can suggest you to look at my code below and test it (you probably have a wav file somewhere in your PC). The adaptation to a mat file should be easy

hope it helps !

clc
clearvars

   
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% FFT parameters
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
NFFT = 2000;    % then df = 1 Hz
OVERLAP = 0.75;


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% load signal
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

[signal, Fs]=audioread('09_52_00.wav');
dt = 1/Fs;

[samples,channels] = size(signal);

% time vector 
time = (0:samples-1)*dt;


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% display 1 : time domain plot
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
figure(1),
plot(time,signal);grid on
title(['Time plot  / Fs = ' num2str(Fs) ' Hz ']);
xlabel('Time (s)');ylabel('Amplitude');

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% display 2 : averaged FFT spectrum
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

[freq, spectrum_raw] = myfft_peak(signal,Fs,NFFT,OVERLAP);

figure(2),plot(freq,20*log10(spectrum_raw));grid on
df = freq(2)-freq(1); % frequency resolution 
title(['Averaged FFT Spectrum  / Fs = ' num2str(Fs) ' Hz / Delta f = ' num2str(df,3) ' Hz ']);
xlabel('Frequency (Hz)');ylabel('Amplitude (dB)');

function  [freq_vector,fft_spectrum] = myfft_peak(signal, Fs, nfft, Overlap)
% FFT peak spectrum of signal  (example sinus amplitude 1   = 0 dB after fft).
% Linear averaging
%   signal - input signal, 
%   Fs - Sampling frequency (Hz).
%   nfft - FFT window size
%   Overlap - buffer percentage of overlap % (between 0 and 0.95)

[samples,channels] = size(signal);

% fill signal with zeros if its length is lower than nfft
if samples<nfft
    s_tmp = zeros(nfft,channels);
    s_tmp((1:samples),:) = signal;
    signal = s_tmp;
    samples = nfft;
end

% window : hanning
window = hanning(nfft);
window = window(:);

%    compute fft with overlap 
 offset = fix((1-Overlap)*nfft);
 spectnum = 1+ fix((samples-nfft)/offset); % Number of windows
%     % for info is equivalent to : 
%     noverlap = Overlap*nfft;
%     spectnum = fix((samples-noverlap)/(nfft-noverlap));	% Number of windows

    % main loop
    fft_spectrum = 0;
    for i=1:spectnum
        start = (i-1)*offset;
        sw = signal((1+start):(start+nfft),:).*(window*ones(1,channels));
        fft_spectrum = fft_spectrum + (abs(fft(sw))*4/nfft);     % X=fft(x.*hanning(N))*4/N; % hanning only 
    end
    fft_spectrum = fft_spectrum/spectnum; % to do linear averaging scaling

% one sidded fft spectrum  % Select first half 
    if rem(nfft,2)    % nfft odd
        select = (1:(nfft+1)/2)';
    else
        select = (1:nfft/2+1)';
    end
fft_spectrum = fft_spectrum(select,:);
freq_vector = (select - 1)*Fs/nfft;
end

[Mathieu NOE]

hello again

problem solved ?