Page 206 - Asterisk™: The Future of Telephony

Sign-bit Cord-bit Step-bit
11
10

11 Low accuracy
01
00
11
0
10
10 Reduced accuracy
01
00
11
01 10 Accurate
01
00
Amplitude 00 11 10 01 00 10 01 11 Highly accurate
00
Highly accurate
00
01 01 Accurate
10
11
00
01
10 Reduced accuracy
10
1
11
00

01
11 Low accuracy
10

11
Samples

Figure 7-11. Five-bit companding
A quantized sample might look like Figure 7-12. It yields the following bit stream:
00000 10011 10100 10101 01101 00001 00011 11010 00010 00001 01000 10011
10100 10100 00101 00100 00101 10101 10011 10001 00011 00001 00000 10100
10010 10101 01101 10100 00101 11010 00100 00000 01000
Aliasing

If you’ve ever watched the wheels on a wagon turn backward in an old Western movie,
you’ve seen the effects of aliasing. The frame rate of the movie cannot keep up with the
rotational frequency of the spokes, and a false rotation is perceived.

178 | Chapter 7: Understanding Telephony