166
|
5 Methods for Discrete Processing and Analysis of Biosignals
0
1
2
3
4
5
time t /s
-1
-0.5
0
0.5
1
amplitude
without noise
with noise
0
2
4
6
8
10
frequency f / Hz
-300
-200
-100
0
amplitude / dB
without noise
with noise
0
1
2
3
4
5
time t /s
-1
-0.5
0
0.5
1
amplitude
averaged
with noise
0
2
4
6
8
10
frequency f / Hz
-300
-200
-100
0
amplitude / dB
averaged
with noise
0
1
2
3
4
5
time t /s
-1
-0.5
0
0.5
1
amplitude
averaged
with noise
0
2
4
6
8
10
frequency f / Hz
-300
-200
-100
0
amplitude / dB
averaged
with noise
0
5
10
15
20
25
30
35
40
45
50
Number of averages N
5
10
15
20
25
SNR / dBc
Fig. 5.12: Coherent averaging using the example of a noisy periodic signal (top left): after a 5-fold
(centre left) and after a 50-fold coherent averaging (bottom left); the spectra of the signals compared
to the non-noisy signal (top right) and the noisy signals (centre right, bottom right) clearly shows
the reduction of the signal-noise-distance. The greater the number of averages N, the better the SNR
in dBc (bottom).
%% graphical representation of the SNR
subplot(4,2,7:8);
plot(1:N,SNR)
xlabel('Number of averages N');
ylabel('SNR / dBc');