這方面的內容忘得差不多了

給你找一個程式 你看看吧：

close all

%

fs=30;

t=0:1/fs:200;

x6=sin(2*pi*2*t)+sin(2*pi*4*t);

x66 = hilbert(x6);

xx = abs(x66+j*x6);

figure(1)

hold on

plot(t,x6);

plot(t,xx,"r")

xlim([0 5])

hold off

% 包絡演算法，未考慮邊界條件

d = diff(x6);

n = length(d);

d1 = d(1:n-1);

d2 = d(2:n);

indmin = find(d1.*d2

indmax = find(d1.*d20)+1;

envmin = spline(t(indmin),x6(indmin),t);

envmax = spline(t(indmax),x6(indmax),t);

figure

hold on

plot(t,x6);

plot(t,envmin,"r");

plot(t,envmax,"m");

hold off

xlim([0 5])