How do I use a loop to remove all of the noise signal segments?

So there is a signal that has 0.5 secs of silence, followed by 1 sec worth of noise, another 0.5 secs of silence, and 1 sec sine wave starting at 100Hz. This pattern continues until the sine wave reaches 1000Hz. I need to use a loop to remove the noises and silence to preserve the sine waves segments. Any tips on how I can do this? Thank you!

[Jon]

Could you please attach an example signal?

[Francisco Cano]

It's a signal of noise, silence and sine waves. It starts out with 0.5secs of noise, 0.5 secs of silence, and then a sec long sine wave. After the first 0.5 secs of noise and 0.5 of silence, it starts with a 100Hz sine wave and does this 10 times until it reachs a 1000Hz sine wave

[dpb]

If you want somebody to play with your signal, make it easy for them...attach a .mat file with some sample data; don't expect somebody else to try to reproduce your data for you....

[Francisco Cano]

Oh sorry! I will attach it to this comment. Thank you again.

Answer 1

[Chunru]

load signal

% detect the env
y = sqrt(2)* movstd(x, [200 200]);

figure
plot(x); hold on
plot(y)

% extract signal 
z = x(y>0.8);

figure
spectrogram(z, 2048, 1024)