System information

important point: the quality of the digitally encoded waveform is affected by the reso-
lution and rate at which it is sampled. At too low a sampling rate, and with too low a
sample resolution, the audio quality will not be acceptable.
Increasing the sampling resolution and rate
Let’s take another look at our original waveform, this time using 5 bits to define our
quantization intervals (Figure A-7).
Figure A-7. The same waveform, on a higher-resolution overlay
In reality, there is no such thing as 5-bit PCM. In the telephone network,
PCM samples are encoded using 8 bits. Other digital audio methods
may employ 16 bits or more.
We’ll also double our sampling frequency. The points plotted this time are shown in
Figure A-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 A-9.
604 | Appendix A: Understanding Telephony