Digital Signal Processing Reference
In-Depth Information
Si gnal s
Time domain
AM-Generator
LP Filter
2, 0
1, 5
1, 0
0, 5
0, 0
-0,5
-1,0
-1,5
-2,0
4
3
2
1
0
-1
-2
-3
-4
1, 00
0, 75
0, 50
0, 25
0, 00
-0,25
-0,50
-0,75
-1,00
-1,25
50
100
200
300
400
500
600
700
800
900
ms
Illustration 23:
Signal and information
A generator module produces in the first instance three different signals the lower two of which are subse-
quently "manipulated". The information value of the above signals increases from the top to the bottom.
The signal above is a sine whose course can be predicted exactly. After a time there is therefore no new
information. The middle signal is a modulated sine signal, the amplitude follows a certain sinusoidal pat-
tern. Finally the signal bottom right has a rather "random" course (it is filtered noise). It can be least well
predicted but contains, for example, all the information about the special characteristics of the filter.
As an example first choose a periodic sawtooth voltage with the period length T = 10 ms
(Frequency f = 200Hz). If one listens carefully several tones of different frequency can
be heard. The higher the tone the weaker they seem in this case. If one listens longer one
finds that the second lowest tone is exactly one octave higher than the lowest, i.e. twice
as high as the base tone.
In the case of all the other periodic forms of signal there are several tones to be heard
simultaneously. The triangle signal in Illustration 22 sounds soft and round, very similar
to a recorder note. The "saw tooth" sounds much sharper, more like the tone of a violin.
In this signal there are more stronger high tones (overtones) than in the "triangle".
Apparently the overtones contribute to the sharpness of the tone.
