Audio encoding and decoding system realizing vector quantization using code book in communication system

Abstract

An audio encoding-decoding system is constructed between a transmitting station and a receiving station which are connected together through communication lines. The transmitting station corresponds to an encoder which performs an encoding process on audio signals input thereto to produce compressive coded bit streams. Herein, the encoder uses a code book or conjugate structure code books to perform vector quantization on residual signals corresponding to residuals of an analysis of linear predictive coding which is performed on the audio signals. Indexes are produced in response to a result of the vector quantization. The encoder produces the compressive coded bit stream based on the indexes and a result of the analysis of the linear predictive coding. A bit rate mode is determined for the compressive coded bit stream in response to conditions of the communication lines. For example, when a congestion occurs in communications of the communication lines, the bit rate mode designates a low bit rate, so that the encoder reduces an amount of information of the bit stream by eliminating a part of the indexes which has a low influence to reproduction of the audio signals, e.g., a part of the indexes which corresponds to high frequency components of the audio signals. The receiving station corresponds to a decoder which receives the compressive coded bit streams which are transmitted thereto via the communication lines together with the bit rate mode. The decoder performs a decoding process, which is reverse to the encoding process of the encoder, on the compressive coded bit streams in response to the bit rate mode.

Dependencies are inferred from the claim text.