| 摘要 |
A vocoder transmitter (12) sends coded speech to a vocoder receiver (16) over a limited-bandwidth channel (14). The transmitter includes a LPC-residual-based first gain estimator (46), which gain value works well with women's voices, but less so with men's. A second, analysis-by-synthesis, gain estimator (42) therein, uses a unit-gain version (342) of the receiver's synthesizer, whose input (24) and output (310) speech power is estimated, to produce the second gain value from their ratio (312). The second gain value has been found to work well with men's voices, but to produce "explosive" artifacts with women's. A combiner (518) weights these two gain estimates, under control of the estimated pitch, to produce the vocoder gain estimate transmitted to the vocoder receiver (16). In a particular embodiment the first gain estimate predominates at low pitch periods, and the second gain estimate at higher ones, with crossover at about 45 sample lags for an 8000 Hz sampling rate.
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