echo on
%  This script will add white Gaussian Noise to a 60 Hz sinusoid
%  at SNRs of 2 and 1/4.  The signal statistics and spectrum are
%  presented in plots.
%  Hit any key to continute ...
pause
t= [0:1023]/4096;    %  time axis, sampling rate 4096 Hz
f= 4096*[0:1023]/1024;    %  frequency axis for FFT
noise25 = sqrt(.25)*randn(1,1024); % Create noise array with average power .25 watts.
sig1 = sqrt(2)*cos(2*pi*60*t); % Create signal with average power 1 watt.
figure(1); plot(t,noise25); xlabel('Seconds'); ylabel('Volts'); title('Noise')
%  Hit any Key to continue
pause
%  Create a histogram of the noise samples with 20 bins
[n, x] = hist(noise25,20);
figure(2); bar(x,n); xlabel('Volts'); ylabel('Frequency of Occurrence'); title('Histogram of Noise Voltages');
%  Hit any Key to continue
pause

%  Create and plot signal plus noise
signo = sig1 + noise25;
figure(3); plot(t, signo); xlabel('Seconds'); ylabel('Volts'); title('Signal Plus Noise')
%  Hit any Key to continue
pause
%  Plot signal in the frequency domain
spec = fft(signo)/(4096*.25);  % Scale by sampling rate and segment duration
figure(4); plot(f(1:512), abs(spec(1:512))); xlabel('Hertz'); ylabel('Volts'); title('Signal Plus Noise Magnitude Spectrum')
%  Hit any Key to continue
pause
%  Increase noise power to 16 watts and plot;  Hit any key to continue
pause
noise16 = sqrt(16)*randn(1,1024); % Create noise array with average power 4 watts.
figure(1); plot(t,noise16); xlabel('Seconds'); ylabel('Volts'); title('Noise')
%  Hit any Key to continue
pause
%  Create a histogram of the noise samples with 20 bins
[n, x] = hist(noise16,20);
figure(2); bar(x,n); xlabel('Volts'); ylabel('Frequency of Occurrence'); title('Histogram of Noise Voltages');
%  Create and plot signal plus noise
%  Hit any Key to continue
pause
signo = sig1 + noise16;
figure(3); plot(t, signo); xlabel('Seconds'); ylabel('Volts'); title('Signal Plus Noise')
%  Hit any Key to continue
pause
%  Plot signal in the frequency domain
spec = fft(signo)/(4096*.25);  % Scale by sampling rate and segment duration
figure(4); plot(f(1:512), abs(spec(1:512))); xlabel('Hertz'); ylabel('Volts'); title('Signal Plus Noise Magnitude Spectrum')
echo off