Block diagram of digital speech transmission:
The speech is transformed by an encoder into a sequence of bits,transmitted over a channel, and then converted back into an audible signal.
Speech is often coded as parameters that represent the signal economically while still allowing speech reconstruction at the receiver with minimal loss.
The terms coding and coder include both the analysis and the synthesis stages of speech processing:
"whatever is done by the encoder must be undone by decoder, to reproduce the output speech".
- motivation:
to develop systems for transmission of speech over low - bandwith telegraph cables
- first analysis - synthesis method
Advantages:
- easier to manipulate
- combination with other data
- it has improved quality and reliability
- can be made secure
- digital encryption stronger then analog "scrambling"
why?
- to minimize transmission cost
- to provide cost - effective storage
- to conserve bandwith
- to consereve disk space in voice storage system
- voice communication
- voice mail
- pager messages
- teleconferencing
- land - line telephone
- satellite telephony
- secure communication