sound generation using MATLAB

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kartik singh
kartik singh 2019-3-14
评论： Stephan 2019-3-14
clc;
clear all;
close all;
fs=24000; %sampling frequency
f=100000; %frequency of the sound wave
t=0:1/fs:10;
y=sin(2*pi*f*t);
sound(y);
I generated a sound wave using the above code. Why is it audible? I set its frequency to more than 20kHz which is the limit of the human ear.
what's wrong here? Does it have to do with the speakers? or the code?

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采纳的回答

Image Analyst
Image Analyst 2019-3-14
It's called aliasing. Sampling at rate lower than the Nyquist frequency will give signals that look like they are oscillating at a lower frequency. See the Wikipedia article on it: Wikpedia on Aliasing
Aliasing_between_a_positive_and_a_negative_frequency.png

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Stephan
Stephan 2019-3-14
Hi,
think about your sampling frequency. Can it really work to sample a signal of 100kHz with a sample rate of 24kHz? Or do you get some useless stuff?
Consider:
fs=2.4; %bad sampling frequency
fs2 = 240 % good sampling frequency
f=10; %frequency of the sound wave
t=0:1/fs:2;
t2 = 0:1/fs2:2;
y=sin(2*pi*f.*t);
y2=sin(2*pi*f.*t2);
plot(t,y,t2,y2)
which gives the following plot:
bad_fs_vs_good_fs.PNG:
This does not look rigth for the blue line which corresponds to a much too low sample frequency. The higher sample rate gives a correct result.
https://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theorem
Best regards
Stephan
  2 个评论
kartik singh
kartik singh 2019-3-14
Thanks for the answer. My query got cleared.
Stephan
Stephan 2019-3-14
Did you notice, that you can accept useful answers and or vote for them? Feel free to do so, if the contributions were useful.

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