MAS.632 Conversational Computer Systems - MIT OpenCourseWare

Spmcb ldg
1000
9OO
*0 4) 700
= 600
a
S
500
cc 400
Time
o80
300
200
100
8o0
600
400
C,
V 200
=
100
2 80
cc 60
40
Time
Figure 3.12. Use of a logarithmic scale disperses the signal density over
the range of the coder. The top figure shows a linearly encoded signal; the
bottom shows the same signal logarithmically encoded.
compensate for this effect, sampling rates significantly in excess of the Nyquist
rate (e.g., in the range of 16 to 32 kHz) are usually used. The second error mode
occurs when the delta-modulated signal has a low value such as in moments of
silence. The reconstructed signal must still alternate up and down (see the right
side of Figure 3.14) as the 1-bit coder cannot indicate a "no-change" condition.
This is called quieting noise.
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