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2. CHARACTERISTICS OF TELEPHONE
LINE (ANALOG)
2.1
Telephone Line Band
A human voice spectrum has the characteristics shown in Fig. A-3.
The greater part of voice energy is concentrated between 0 to 4000 Hz as
shown in the Fig. A-3. That is, if this frequency band is transmitted, the
naturalness of the voice will be slightly lost. However, the content (infor-
mation) of the telephone conversation can be satisfactorily transmitted.
For this reason, telephone lines are designed for voice transmission in a
frequency bandwidth of 300 to 3400 Hz.
A–4
40
30
20
10
0
2000
4000
Fig. A-3 Voice Spectrum
0
-3
The band of telephone lines
0
300
1000
Fig. A-4 Ideal Frequency Characteristics of a Telephone Lines
Telephone line
frequency band
6000
8000
10000
Frequency (Hz)
2000
3000
Frequency (Hz)
12000
3400
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