Click in the beginning and end of pure tone

I am wondering why there is a kind of clicking sound in the beginning

but especially in the end of a pure tone.

What I am doing:

spl_rms = 60;
spl_p0 = 20e-6;
spl_max = spl_p0 * 10^(60/20) * sqrt(2);          
fs = 20000;
fsig = 1000;
n = 0:1*fs - 1;
t = n/fs;
sig = spl_max*sin(2*pi*fsig*t);
sound(sig, fs);

What is the reason for this clicking sound in the end?

What can I do against it, so how can I modify `sig` to improve this?

[Rik]

I don't see any reason why that would be the case. Are you sure the problem is in Matlab and not your audio device?

You could try to add a low amplitude signal (essentially 0) at the end of sig, to see whether the click is at the end of any sound() call, or whether is is in your signal.

[Dominik Deml]

Sorry, my fault. It is not because of Matlab, it is because of my audio device BUT I want to use Matlab to fix this problem.

Answer 1

[Les Beckham]

Try adding ramps at the beginning and end to avoid the discontinuities of starting and stopping the tone.

spl_rms = 60;
spl_p0 = 20e-6;
spl_max = spl_p0 * 10^(60/20) * sqrt(2);          
fs = 20000;
fsig = 1000;
n = 0:1*fs - 1;
t = n/fs;
sig = spl_max*sin(2*pi*fsig*t);

ramp = linspace(0, 1, 200);
sig(1:200) = sig(1:200) .* ramp;
sig(end-199:end) = sig(end-199:end) .* flip(ramp);
tiledlayout('Horizontal', 'TileSpacing', 'compact')
nexttile
plot(sig)
xlim([1 500])
grid on
nexttile
plot(sig)
xlim([19500 20000])
grid on

% sound(sig, fs);

[Dominik Deml]

This sounds way better than the original sound, thanks! But I still don't understand what causes this problem. What do the discontinuities in the end effect? Do the discontinuities add new frequencies?

[Les Beckham]

Your are quite welcome.

Absolutely, the discontinuities add new frequencies to the sound. When you have what amounts to a step in the sound amplitude it creates a very high frequency (which you hear as the "click").

Thank you for accepting the answer.

[Dominik Deml]

Wow, thank you so much!

[Les Beckham]

You are quite welcome.