How to create an envelope on a specific signal

could anybody please guide me how i can find the lower & upper envelope on a signal? would you give me a simple example?thank you

Answer 1

[Star Strider]

Use the hilbert function:

t = linspace(0,5*pi,1000);
s = sin(t) .* cos(15*t);
hs = hilbert(s);

figure(1)
plot(t, s)
plot(t,-abs(hs),'r-', t,abs(hs),'-r', 'LineWidth',1.5)
hold off
grid

produces:

[maryam]

thank you very much. it is very helpful :)

[Star Strider]

My pleasure!

[Taher Sahara]

In the envelope created as in the image if I want to find the width of one wave packet how can I do that? Please help

[Star Strider]

Taher Sahara — Post this as a new Question.

[Saeed Haidar]

hello guys,

can someone help me create an envelope to my signal, here's the code:

fs = 44100;
c5=key(52,8,fs);
a4=key(49,8,fs);
b4=key(51,8,fs);
e4=key(44,8,fs);
e5=key(56,8,fs);
d5=key(54,8,fs);
f5=key(57,8,fs);
line1= [ e4 a4 b4 c5 a4 ];
line2= [ e4 a4 b4 c5 a4 ];
line3= [ e4 a4 b4 c5 b4 a4 c5 b4 a4 e5 e5 e5 d5  e5 f5 f5];
song=[line1 line2 line3];
sound(song,fs,24);
function wave= key(p,n,fs)
t=0:1/fs:4/n;
idx=440*2^((p-49)/12);
tt=4/n:1/fs:0;
wave=(sin(2*pi*idx*t)).*exp(tt);
wave=wave./max(wave);
end

[Scott MacKenzie]

@Saeed Haidar. You comment is about something quite different -- adding an envelope (attack, sustain, decay) to the notes in a melody. If you are still interested in this, please post as a separate question.