Digital Signal Processing Reference
In-Depth Information
G enerator
Formula
Dat a window
Time domain
List
Spectrum
Fr eq. dom ain
Slider
8
0,0125
Sample rate 1024
Bandwidth 208 Hz (516Hz)
7
0,0100
6
0,0075
5
4
0,0050
3
0,0025
2
0,0000
1
0
-0,0025
50
55
60
65
70
75
80
85
90
95
100
110
120
-350
-300
-250
-200
-150
-100
-50
0
50
100
150
200
250
300
ms
Hz
Sample rate 64
Bandwidth
13 Hz (26 Hz)
Illustration 216:
Digital lowpass with “smooth” conducting state region
By adding a suitable window (e.g. a “HAMMING” window) the Si-function begins and ends gently, i.e.
there are no steps at the beginning or the end of the time segment of (here) 1s. But the curve of the Si-func-
tion is changed as a result, as the whole signal segment is “weighted” by it. The effect is to make the curve
in the conducting state region straighter and the edge steepness decreases somewhat.
While the bandwidth of the lowpass at the top is 13 Hz, in the circuit at the bottom it is 64 Hz although the
same filter coefficients were used. The reason is the much higher sampling rate of 1024 compared with 64
top). The pulse response of the filter (Si-function) is as a result runs 16 times faster, it lasts only 1/16 of the
original time. According to the Uncertainty Principle the bandwidth must be 16 times as large: 16
<
13 =
208 Hz.
