I am trying to find a 'threshold value' for separation of the noise components and the signal components in the received signal r1. How can I do that?

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Milan Saliya 2015-6-30

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https://ww2.mathworks.cn/matlabcentral/answers/225975-i-am-trying-to-find-a-threshold-value-for-separation-of-the-noise-components-and-the-signal-compon

编辑： Image Analyst 2015-6-30

I want to set all frequency components below that threshold to 0 and store this as a modified filtered spectrum, ( take care for the symmetry of the complex spectrum for a real signal) and inverse FFT this modified spectrum to obtain the corresponding real signal rx. The sequence of tones rx is a received signal after noise suppression, so DTMF codes can be detected. How can I do that?? Please help me

Signal1= 0.5*[ sin(2*pi*f1(5)*t)+sin(2*pi*f2(5)*t)]; 
r1= Signal1+ randn(size(t)); % Random noise signal 
R1= fft(r1, 512); % fft of S1
p= R5.* conj(R5)/512; % power spectrum
f= 1000*(0:256)/512; % frequency scale