Digitization & quantization in telephony
The Nyquist result is used in digitization where a voice-grade signal (of bandwidth 4 kHz) is sampled at 8000 samples/s.
- The inter-sample time (125 usec) is a well-known constant in telephony.
Now each of these analog sample is digitized using 8 bits
- These are also called quantization levels
- This results in a 64kbps voice circuit, which is the basic unit of multiplexing in telephony.
- T-1/T-3, ISDN lines, SONET etc are built using this unit
If the quantization levels are logarithmically spaced we get better resolution at low signal levels. Two ways:
- ?-law (followed in US and Japan), and A-law (followed in rest of world) => all international calls must be remapped.