Adaptive differential pulse code modulation system
AssigneeFujitsu Limited
InventorsTomoyoshi Takebayashi, Kaoru Yamamoto, Tsuyoshi Miyazaki, Kazuo Murano, Hiromi Mori
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Abstract
An adaptive differential pulse code modulation system includes an adaptive quantizer and an adaptive predictor which have a coding characteristic optimized to a voice signal, and a quantizer and a predictor which have a coding characteristic optimized to a voice band MODEM signal. This system is normally used as a coding system optimized to the voice signal, and when this system detects a MODEM training signal, it becomes a coding system optimized to the MODEM signal.
Claims6
An adaptive differential pulse code modulation system, comprising:
- an adaptive quantizer and an adaptive predictor which have a coding characteristic optimized to a voice signal;
- a quantizer and a predictor which have a coding characteristic optimized to a voice band modem signal;
- and
- means, coupled to said adaptive quantizer, said adaptive predictor, said quantizer and said predictor, for detecting a modem training signal and comprising:
- a phase synchronizing circuit which can detect a carrier frequency in a restricted region at a center of the carrier frequency;
- and
- means for detecting whether output power of the carrier frequency is larger than a predetermined threshold value, said modem training signal being detected, after detecting the carrier frequency by detecting that an output of said phase synchronizing circuit has not changed in polarity during a predetermined period, and that the output power is larger than a predetermined threshold value during said predetermined period, said system normally being used as a coding system optimized to said voice signal, and when said system detects a modem training signal, said system becomes a coding system optimized to said modem signal.
An adaptive differential pulse code modulation system, comprising:
- an adaptive quantizer and an adaptive predictor which have coding characteristics optimized to a voice signal;
- a fixed quantizer and a fixed predictor which have coding characteristics optimized to a voice band modem signal;
- and
- means, coupled to said adaptive quantizer, said adaptive predictor, said fixed quantizer and said fixed predictor, for detecting a modem training signal and activating said adaptive quantizer and predictor or said fixed quantizer and predictor, said system normally being used as a coding system optimized to said voice signal, and when said system detects a modem training signal, said system becomes a coding system optimized to said modem signal.
Dependencies are inferred from the claim text.