Simple Signal Smoothing via Signal Averaging using Matlab

posted in: MATLAB (MATrix LABoratory) | 0

Signal averaging is aimed to smooth signals which contain noise. The simple averaging process implemented here is using the idea of adding / summing several sequence of signals which each of them contains random noise. Next, the result of summation process is then divided by number of signal sequence added which then produced an averaged signal which has lower noise level than any of the original single signal. The implementation of the simple signal averaging is carried out using Matlab.

The complete code of signal averaging is shown below added with brief explanations

% taking average of sinusoidal signal with randomized noise
% Jonny Latuny, Feb. 21, 2012

close all; % close all open windows
clear all; % clear all previous / existing variables in workspace

dt = 1/1000; % define dt value
t = dt:dt:200*dt; % devine array of t
sine = sin(2*pi*100*t); % generate a sinusoidal signal based on t value

signal_all = []; % provide empty container to store summation result

for i = 1:10 % perform 10 loops in which 10 parts of signal are produced
y_noisy = sine + randn(size(t)); % signal + randonm noise
eval(['signal_' num2str(i) ' = y_noisy;']); % using eval to generate sequential signal segment
signal_all = [signal_all; eval(['signal_' num2str(i);])]; % concatenate all 10 signal into 1 matrix

signal_avr = sum(signal_all) / i; % calculating the average value

FT = fft(y_noisy,512); % FFT of a single signal
P = FT.* conj(FT)/512; % provide FFT result for plotting

FT_avr = fft(signal_avr,512); % FFT of averaged signal
P_avr = FT_avr.* conj(FT_avr)/512; % provide FFT result for plotting

subplot(2,1,1) % subplot 1
plot(P), axis([0 250 0 30]);
title('Spectrum of Single Signal (10th)');
xlabel('data points');

subplot(2,1,2) % subplot 2
plot(P_avr,'r-'), axis([0 250 0 30]);
title('Spectrum of Averaged Signal');
xlabel('data points');

Plot of Signal Averaging Example












The above composite plot shows the results of the simple signal averaging.

The top subplot shows FFT result of a single signal which contains noise.

The bottom subplot shows FFT result of the averaged signal which calculated using 10 sequences of signal samples as implemented in Matlab codes above.