Branch : Computer Science and Engineering
Subject : Wireless Communication
Speech Coding
Introduction:
Service providers accommodate a limited allocated bandwidth in which they provide a service to more users which makes the bandwidth a precious commodity. Low bit rate speech coding met this challenge and provide a good service within this range. The lower the bit rate at which the coder can deliver toll quality speech, the more speech channels can be compressed within a given bandwidth.The goal of all speech coding systems is to transmit speech with the highest possible quality using the least possible channel capacity
Hierarchy of speech coders:
Figure 15.1 |
Characteristics of Speech Signals:
- Nonuniform probability distribution of speech amplitude
- Nonzero auto-correlation between successive speech samples
- Non-flat nature of the speech spectra
- Existence of voiced and unvoiced segments in-speech
- Quasi-periodicity of voiced speech signals
- The most basic: Speech is band-limited
- The band limited property of speech signals makes sampling possible
- The aforementioned properties allow quantization,