我試圖找到頻譜中的峰值，但我只需要提取基頻及其諧波的峰值，紅色矩形。如何排除基頻之前的任何東西，只包括基頻及其3次諧波。我使用此代碼，但它沒有幫助。任何的想法？
pks = findpeaks(q);
findpeaks(q,'MinPeakDistance',99)
%findpeaks(q,'MinPeakHeight',0.0004)
xlim([0.1 500])
使用時：
Fs = 1000;
t = 0:0.001:1-0.001; % 250-Hz sine wave modulated at 100 Hz
x = [1 cos(2*pi*100*t)].*cos(2*pi*250*t);
%envspectrum(x,Fs)
[ES,F]=envspectrum(x,Fs);
%%
findpeaks(ES,F)
% Now for only > 99 Hz (choose the freq you fancy)
idx = F >= 99; % greater than 99 Hz
findpeaks(ES(idx),F(idx)) % idx only select those F > 99
% Good? Keep the values of amplitud and location (in frequencies) of the ES
[pks,loc] = findpeaks(ES(idx),F(idx));
% If you just want to have the first 5 peaks (or the n? you choose):
% Select only 3 first.
if length(pks) > 3 % Check you didnt get less peaks
pks = pks(1:3);
loc = loc(1:3);
end
% To plot the peaks in the envelope
plot(F(idx),ES(idx),loc,pks,'r*')
我明白了：
結果如下：
uj5u.com熱心網友回復：
編輯以通過示例適應新代碼。我們正在應用信號的包絡頻譜 - [ES,F] = envspectrum(sig,Fs);-，所以我們知道信號及其頻率采樣 (fs)。
還是一樣的程序。您可以僅計算findpeaks()高于 250 Hz 的信號樣本的值。為此，您可以為想要的頻率值定義一個邏輯陣列：
idx = F >= 250; % 250 Hz
并將此邏輯索引應用于您要應用該函式的信號和頻率的包絡頻譜findpeaks()：
[pks,loc] = findpeaks(ES(idx),F(idx));
例子：
% Let's create a signal with fs = 2500 Hz
% This is just to create an example, don't worry about these lines
fs = 2500;
f0 = 25;
n = 8;
d = 0.02;
p = 0.12;
t = 0:1/fs:1-1/fs;
z = [1 0.5 0.2 0.1 0.05]*sin(2*pi*f0*[1 2 3 4 5]'.*t)/5;
% z: our signal
% t: time array of the signal (to plot)
% How does the signal look?
plot(t,z)
% Calculating the envelope signal and its spectrum
[ES,F]=envspectrum(z,fs);
% Plot the envelop if you want:
envspectrum(z,fs)
% ES: Envelope spectrum of the signal
% F: array of frequencies used for the spectrum (half our fs for Nyquist Theorem)
% Find the peaks of the envelope spectrum
% Let's see how it is for all the envelope
findpeaks(ES,F)
% Now for only > 250 Hz (choose the freq you fancy)
idx = F >= 250; % greater than 250 Hz
findpeaks(ES(idx),F(idx)) % idx only select those F > 250
% Good? Keep the values of amplitud and location (in frequencies) of the ES
% Use 'NPeaks' input to tell function to select only 5 first peaks it can find.
[pks,loc] = findpeaks(ES(idx),F(idx), 'NPeaks', 5);
% To plot the peaks in the envelope
plot(F(idx),ES(idx),loc,pks,'r*')
% Note in this example the first peak (in 250 Hz) is not selected
% because is not a local maximum when we narrow the envelope.
% If the function select false peaks somehow, you can use
%'MinPeakHeight' to specify an absolute amplitude, 'MinPeakProminence '
%for a relative amplitude or 'Threshold' inputs for a better fit.
https://uk.mathworks.com/matlabcentral/answers/768537-use-findpeaks-on-specific-frequency-range
https://uk.mathworks.com/help/signal/ref/findpeaks.html#responsive_offcanvas
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標籤：MATLAB