Biomedical Engineering Reference
In-Depth Information
MATLAB provides several windowing functions including these:
w = rectwin(L)
returns a rectangular window of length
L
in the column vector
w
,
L
∈
Z
+
.
w = bartlett(L)
returns an
L
-point Bartlett window in the column vector
w
.
w = hamming(L)
returns an
L
-point symmetric Hamming window in the column vector
w
.
Figures 3.1, 3.2, and 3.3 show the time function of a 65-point window and its
Fourier transform magnitude in decibels for rectangular, Bartlett, and Hamming
windows, respectively.
3.1.1.3 The Autocorrelation Function and Estimation of the Power Spectrum
The spectral characteristics of a deterministic signal can easily be determined using
(3.1) to (3.5). However, the EEG is a highly complex signal and can therefore be
Time domain
Frequency domain
40
1
30
0.8
20
0.6
10
0.4
0
0.2
10
−
20
−
0
0
0.2
0.4
0.6
0.8
10
20
30
40
50
60
Samples
Normalized frequency (
×π
rad/sample)
Figure 3.1
Rectangular window of
L
= 65 and its Fourier transform magnitude in decibels.
Time domain
Frequency domain
40
1
20
0.8
0
0.6
−
20
0.4
−
40
0.2
−
60
−
80
0
0
0.2
0.4
0.6
0.8
10
20
30
40
50
60
Normalized frequency (
rad/sample)
Samples
×π
Figure 3.2
Bartlett window of
L
= 65 and its Fourier transform magnitude in decibels.
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