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A–4

2. CHARACTERISTICS OF TELEPHONE 

LINE (ANALOG)

2.1

Telephone Line Band

A human voice spectrum has the characteristics shown in Fig. A-3.

Fig. A-3   Voice Spectrum

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.

Fig. A-4   Ideal Frequency Characteristics of a Telephone Lines

Telephone line
frequency band

Frequency (Hz)

40

30

20

10

0

2000

4000

6000

8000

10000

12000

V

oice

Le

v

e

l

(dB)

0

-3

300

1000

2000

3000

3400

0

T

ransmittance

(dB)

Frequency (Hz)

The band of telephone lines