Audio encoding and decoding system realizing vector quantization using code book in communication system
First Claim
1. An audio encoding-decoding system comprising:
- an audio encoder which uses a code book to perform vector quantization on residual signals, corresponding to residuals of an analysis of linear predictive coding which is performed on audio signals by certain intervals of time, so as to produce vector quantization indexes, wherein the audio encoder provides a coded output which contains the vector quantization indexes and information representing a result of the analysis of the linear predictive coding;
information quantity control means for performing elimination of indexes which correspond to a part of the vector quantization indexes contained in the coded output of the audio encoder in response to an information quantity control request so as to control an information quantity of the coded output, said information quantity control means also adding information representing a control level of the information quantity to the coded output, wherein the indexes of the elimination correspond to the part of the vector quantization indexes which has low influence on reproduction of audio information; and
an audio decoder for decoding the coded output, whose information quantity is controlled by the information quantity control means, on the basis of the information representing the control level of the information quantity, thus reproducing the audio signals.
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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.
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Citations
14 Claims
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1. An audio encoding-decoding system comprising:
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an audio encoder which uses a code book to perform vector quantization on residual signals, corresponding to residuals of an analysis of linear predictive coding which is performed on audio signals by certain intervals of time, so as to produce vector quantization indexes, wherein the audio encoder provides a coded output which contains the vector quantization indexes and information representing a result of the analysis of the linear predictive coding; information quantity control means for performing elimination of indexes which correspond to a part of the vector quantization indexes contained in the coded output of the audio encoder in response to an information quantity control request so as to control an information quantity of the coded output, said information quantity control means also adding information representing a control level of the information quantity to the coded output, wherein the indexes of the elimination correspond to the part of the vector quantization indexes which has low influence on reproduction of audio information; and an audio decoder for decoding the coded output, whose information quantity is controlled by the information quantity control means, on the basis of the information representing the control level of the information quantity, thus reproducing the audio signals. - View Dependent Claims (2, 3, 4, 5, 6)
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7. An audio encoding-decoding system comprising:
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bit rate control means for determining a bit rate mode in response to conditions of communication lines; an encoder for performing an encoding process on audio signals input thereto, wherein a code book is used to perform vector quantization on residual signals corresponding to residuals of an analysis of linear predictive coding, which is performed on the audio signals, so that the encoder produces a compressive coded bit stream based on a result of the analysis of the linear predictive coding as well as indexes which correspond to a result of the vector quantization, wherein an amount of information of the indexes of the compressive coded bit stream is selectively reduced in response to the bit rate mode, the compressive coded bit stream together with information representing the bit rate mode being transmitted onto the communication lines; and a decoder for receiving the compressive coded bit stream transmitted thereto via the communication lines so as to perform a decoding process which is reverse to the encoding process of the encoder, so that the decoder reproduces the audio signals in response to the information representing the bit rate mode. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14)
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Specification