Page 203 - Asterisk™: The Future of Telephony

01111
01011
01010
01001
01000
00111
00110
00101
00100
00011
00010
Amplitude 00001
00000
10001
10010
10011
10100
10101
10110
10111
11000
11001
11010
11011
11100
1 2 3 4 5 6 7 8 9 10 1112 13 14 15 1617 18 19 202122 23 24 2526 27 28
Samples
Figure 7-8. The same waveform at double the resolution
We’ll also double our sampling frequency. The points plotted this time are shown in
Figure 7-8.
We now have twice the number of samples, at twice the resolution. Here they are:
00111 01000 01001 01001 01000 00101 10110 11000 11001 11001 11000 10111
10100 10001 00010 00111 01001 01010 01001 00111 00000 11000 11010 11010
11001 11000 10110 10001
When received at the other end, that information can now be plotted as shown in
Figure 7-9.
From this information, the waveform shown in Figure 7-10 can then be generated.
As you can see, the resultant waveform is a far more accurate representation of the
original. However, you can also see that there is still room for improvement.

Note that 40 bits were required to encode the waveform at 4-bit reso-
lution, while 156 bits were needed to send the same waveform using 5-
bit resolution (and also doubling the sampling rate). The point is, there
is a tradeoff: the higher the quality of audio you wish to encode, the
more bits required to do it, and the more bits you wish to send (in real
time, naturally), the more bandwidth you will need to consume.

Digital Telephony | 175