Research Review By:
Kroon, Peter Acoustics and Speech Research Department, Bell Laboratories, Lucent Technologies, Murray Hill, New Jersey.
- Speech-compression techniques
- CELP coder
- System attributes
- Low-bit-rate and scalable coders
- Additional Readings
The use of a digital representation for speech signals has many advantages. The signal can be more easily manipulated, combined with other signals such as video or data, and made less sensitive to transmission errors. A drawback of digital representations is that for high-fidelity reproduction the number of bits per second is high. A digital representation can be obtained by sampling the analog signal with a frequency at least twice that of the highest frequency occurring in the signal. For each of the samples, the amplitude has to be encoded with a digital number. The most simple form of coding is pulse-code modulation (PCM), which requires 8–16 bits per sample. A telephone-bandwidth (200–3400 Hz) speech signal is typically sampled 8000 times per second by using 8–12 bits per sample. The resulting bit rate for the digital representation is 64,000–96,000 bits per second.
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