Speech encoding communication system

Abstract

A speech encoding communication system for use with a land mobile radio telephone system which decreases an unfamiliar feeling to a sound output caused by a cyclic tone variation of background noise. On the transmission side, an audition weighting filter selectively receives a sound signal or an output of a low-pass filter for the sound signal in response to VOX mode information. In a sound absent condition based on the VOX mode information, a power quantizer outputs a power index calculated by an average of the power over a long period, and an LPC analyzer outputs a unique value as an LPC and an LSP quantizer outputs a quantized LSP index and a quantized LPC obtained when the LPC has the unique value in the sound absent condition. Further, an adaptive codebook search unit controls an adaptive codebook index to a unique value without performing searching processing. On the reception side, a power controller receives a quantized power, VOX mode information and a sound signal. When the VOX mode information represents a sound absent interval and background noise is to be produced, the power controller calculates an average of the quantized power over a long period and controls the power of the sound signal.