Sine wave changing amplitude

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Nuchto
Nuchto 2014-11-6
评论： chirag hb 2018-1-22
Can you have a sine wave with varying amplitudes? I think this concept does not exist.

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回答（3 个）

Image Analyst
Image Analyst 2014-11-6
See attached demo (make_wav_file.m, below the plot) where I vary the amplitude and frequency of a sound wave.
  2 个评论
Tahariet Sharon
Tahariet Sharon 2017-10-27
编辑：Tahariet Sharon 2017-10-27
Yes, but the initial qustion was about changing the amplitude of a SINE wave, not a complex wave.
Image Analyst
Image Analyst 2017-10-27
My demo DOES modify the amplitude of a sine wave. Perhaps you overlooked this line of code in it:
% Construct the waveform:
y = int16(Amplitude .* sin(2.*pi.*t./T));
The amplitude array is changing according to 2 ways in my demo: an exponential decay and another lower frequency since wave, but you could alter the amplitude in whatever way you want. So I'm not sure why the "but" is in your comment.

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Orion
Orion 2014-11-6
编辑：Orion 2014-11-6
Sure you can.
a sine wave is defined by
y = A*sin(w*t+phi).
if you define A as a function(vector) dependant of the time, then you get a sine wave with varying amplitudes.
t = 0:0.01:10;
w = 8*pi;
phi = 0;
A = floor(t); % why not
y = A.*sin(w*t+phi);
plot(t,y);
I did it in matlab, but you can obviously do it with simulink (don't know what tool you're using).
Youssef Khmou
Youssef Khmou 2014-11-6
Nuchto, That is the amplitude modulation, it is possible to simulate that type of signals:
x=real(exp(j*2*pi*(0:0.1:10)));
y=rand(size(x)).*x;
subplot(1,2,1), plot(x);
subplot(1,2,2); plot(y): title(' random amplitude');
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Image Analyst
Image Analyst 2014-11-7
But sometimes the imaginary part is zero. Here is the table:
Time Domain Frequency Domain
real hermitian (real=even, imag=odd)
imaginary anti-hermitian (real=odd, imag=even)
even even
odd odd
real and even real and even (i.e. cosine transform)
real and odd imaginary and odd (i.e. sine transform)
imaginary and even imaginary and even
imaginary and odd real and odd

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