Adaptive rematrixing of matrixed audio signals

An adaptive audio encoding matrix, comprising

• 4:2 audio matrix means receiving four audio source signals L, C, R, and S for providing two matrix encoded audio signals L.sub.T and R.sub.T in response thereto, and
• means for adaptively changing the matrix encoding characteristics of said 4:2 audio matrix means such that the matrix means provides as its output two signals L.sub.T and R.sub.T generally in accordance with the relationships
• L.sub.T =L+0.707C+0.707S,
• and
• R.sub.T =R+0.707C-0.707S
• when L.sub.T or R.sub.T has the smallest amplitude among L.sub.T, R.sub.T, k(L.sub.T +R.sub.T), and k(L.sub.T -R.sub.T) and provides as its output two signals L.sub.T ' and R.sub.T ' generally in accordance with the relationships ##EQU5## when k(L.sub.T +R.sub.T) or k(L.sub.T -R.sub.T) has the smallest amplitude among L.sub.T, R.sub.T, L.sub.T ' and R.sub.T 'where k is a constant.

An adaptive 4:2 audio matrix and encoder for a signal transmission or storage and retrieval system, said matrix and encoder adapted to receive four audio input signals, comprising

• 4:2 matrix means receiving said four input signals for providing two matrix output signals,
• means for dividing the matrix output signals into frequency components,
• bit-rate reduction encoding means, said bit-rate reduction encoding means having a noise level which varies with signal amplitude level, and
• adaptive rematrixing means for determining which of the signals among the matrix output signals and the sum and difference of the matrix output signals has the smallest amplitude, and for applying frequency components representing the matrix output signals to the coding, transmission, or storage and retrieval if one of the matrix output signals has the smallest amplitude and for applying frequency components representing the sum and difference of the matrix output signals to the coding, transmission, or storage and retrieval if one of the sum and difference of the matrix output signals has the smallest amplitude.

In a system for coding, transmission, or storage and retrieval of audio signals received from a 4:2 audio signal encoding matrix and applied to a complementary 2:4 audio decoding matrix, the system having a noise level which varies with signal amplitude level, apparatus comprising

• means for determining which of the signals among the encoding matrix output signals and the sum and difference of the encoding matrix output signals has the smallest amplitude,
• means for applying the encoding matrix output signals to the coding, transmission, or storage and retrieval if one of the encoding matrix output signals has the smallest amplitude and for applying the sum and difference of the encoding matrix output signals to the coding, transmission, or storage and retrieval if one of the weighted sum and weighted difference of the encoding matrix output signals has the smallest amplitude, said means for applying also applying a control signal to the coding, transmission, or storage and retrieval indicating if the encoding matrix output signals or the sum and difference of the encoding matrix output signals is being applied to the transmission or storage, and
• means receiving said matrix output signals or the sum and difference of the matrix output signals, and said control signal from the coding, transmission, or storage and retrieval, said means recovering unaltered, for use by the complementary 2:4 decoding matrix, the received signals when said means for applying applied the matrix encoder output signals to the coding, transmission, or storage and retrieval and for recovering the sum and difference of the received signals, for use by the complementary 2:4 decoding matrix, when the means for applying applied the sum and difference of the matrix encoder output signals to the coding, transmission, or storage and retrieval.

In a 4:2:4 matrix system for coding, transmission, or storage and retrieval of four audio signals on a two-channel medium, the system having a channel noise level which varies with signal amplitude level, apparatus comprising

• 4:2 audio encoding matrix means receiving said four audio signals for providing two matrix encoded output signals,
• adaptive rematrixing means for determining which of the signals among the encoding matrix output signals and the sum and difference of the encoding matrix output signals has the smallest amplitude, and for applying the encoding matrix output signals to the coding, transmission, or storage and retrieval if one of the encoding matrix output signals has the smallest amplitude and for applying the sum and difference of the encoding matrix output signals to the coding, transmission, or storage and retrieval if one of the sum and difference of the matrix output signals has the smallest amplitude, said adaptive matrix means also applying a control signal to the coding, transmission, or storage and retrieval indicating if the encoding matrix output signals or the sum and difference of the encoding matrix output signals is being applied to the coding, transmission, or storage and retrieval,
• decode adaptive rematrixing means receiving said encoding matrix output signals or the sum and difference of the encoding matrix output signals and said control signal from the coding, transmission, or storage and retrieval, said means recovering the received signals unaltered when said adaptive rematrixing means applied the matrix encoder output signals to the coding, transmission, or storage and retrieval and for recovering the sum and difference of the received signals when the adaptive rematrixing means applied the sum and difference of the matrix encoder output signals to the coding, transmission, or storage and retrieval, and
• complementary 2:4 audio decoding matrix means receiving the unaltered received signals or the sum and difference of the received signals for providing four matrix output signals representing the four audio signals applied to the 4:2 audio matrix encoding means.

An adaptive audio encoding and decoding matrix system for use with signal coding, transmission, or storage and retrieval, comprising

• adaptive 4:2 audio matrix means receiving four audio source signals L, C, R, and S for providing two matrix encoded audio signals L.sub.T and R.sub.T in response thereto for application to signal coding, transmission, or storage, the output signals L.sub.T and R.sub.T having characteristics such that
• L.sub.T =L+0.707C+0.707S,
• and
• R.sub.T =R+0.707C-0.707S
• when L.sub.T or R.sub.T has the smallest amplitude among L.sub.T, R.sub.T, k(L.sub.T +R.sub.T), and k(L.sub.T -R.sub.T), where k is a constant, and the output signals L.sub.T and R.sub.T having characteristics such that ##EQU11## when L.sub.T ' or R.sub.T ' has the smallest amplitude among L.sub.T, R.sub.T, L.sub.T ' and R.sub.T ', said means for adaptively changing the matrix encoding characteristics of said 4:2 audio matrix also producing a control signal indicating which set of relationships define the output signals L.sub.T, R.sub.T, L.sub.T ' and R.sub.T ', and
• complementary adaptive 2:4 audio matrix decoding means receiving said signals L.sub.T and R.sub.T or L.sub.T ' and R.sub.T ' along with said control signal from said coding, transmission, or storage and retrieval for providing four decoded signals L', C', R' and S' representative of said four audio source signals.

Apparatus for use in a signal coding, transmission, or storage and retrieval system in which audio signals are divided into frequency components and the frequency components are subject to bit-rate reduction encoding before application to the coding, transmission, or storage and retrieval, and the encoded signals from the coding, transmission, or storage and retrieval are subject to bit-rate reduction decoding and the decoded frequency components are assembled into representations of the audio signals applied to the system, the system having a noise level which varies with signal amplitude, the system receiving the two audio output signals of a 4:2 audio signal encoding matrix and the system applying the representations of the audio signals to a 2:4 audio signal decoding matrix, comprising

• adaptive rematrixing means receiving said frequency components for determining which of the signals among the encoding matrix output signals and the sum and difference of the encoding matrix output signals has the smallest amplitude, and for applying frequency components representing the encoding matrix output signals to the bit-rate reduction encoding if one of the encoding matrix output signals has the smallest amplitude and for applying the sum and difference of the encoding matrix output signals to the bit-rate reduction encoding if one of the sum and difference of the matrix output signals has the smallest amplitude, said adaptive matrix means also producing a control signal indicating if frequency components representing the encoding matrix output signals or the sum and difference of the encoding matrix output signals are being applied to the bit-rate reduction encoding, and
• decode adaptive rematrixing means receiving said control signal and frequency component representations of said encoding matrix output signals or the sum and difference of the encoding matrix output signals from the bit-rate reduction decoding, said means recovering the received signals unaltered when said adaptive rematrixing means applied frequency representations of the matrix encoder output signals to the bit-rate reduction encoding and recovering frequency component representations of the sum and difference of the received signals when the adaptive rematrixing means applied frequency representations of the sum and difference of the matrix encoder output signals to the coding, transmission, or storage and retrieval.

In a system in which the noise level varies with signal amplitude level, apparatus for adaptively rematrixing signals received from coding, transmission, or storage and retrieval in response to a control signal also received from the coding, transmission, or storage and retrieval for applying the adaptively rematrixed signals to a 2:4 audio decoding matrix, the received signals resulting from encoding by a 4:2 audio signal encoding matrix and adaptive rematrixing of the encoding matrix output signals such that in one state of the adaptive rematrixing the signals applied to the coding, transmission, or storage and retrieval are the output of the encoding matrix and in another state of the adaptive rematrixing the signals applied to the coding, transmission, or storage and retrieval are the amplitude weighted sum and difference of the output of the encoding matrix, said control signal indicating the state of the adaptive rematrixing, comprising

• decode adaptive rematrixing means receiving said matrix output signals or the amplitude weighted sum and difference of the matrix output signals from the coding, transmission, or storage and retrieval for producing audio signals representing the output of said 4:2 encoding matrix for application to said 2:4 decoding matrix, said means having a first state for recovering the signals unaltered from the coding, transmission, or storage and retrieval and a second state for recovering the sum and difference of the signals from the coding, transmission, or storage and retrieval, and
• means receiving said control signal from said coding, transmission, or storage and retrieval for controlling said decode adaptive rematrixing means in response to said control signal, such that the decode adaptive rematrixing means operates in said first state when the matrix encoder output signals are applied to the coding, transmission, or storage and retrieval and the decode adaptive rematrixing means operates in said second state when the sum and difference of the matrix encoder output signals are applied to the coding, transmission, or storage and retrieval.

In a system in which the noise level varies with signal amplitude level, apparatus for adaptively matrix decoding signals received from coding, transmission, or storage and retrieval in response to a control signal also received from the coding, transmission, or storage and retrieval, the received signals resulting from encoding of four audio source signals prior to application to said coding, transmission, or storage and retrieval by adaptive 4:2 audio signal matrix encoding such that in a second state of the adaptive matrix the matrix outputs are the sum and difference of the outputs of the adaptive matrix in its first state, said control signal indicating the state of the adaptive matrix, comprising

• decode adaptive dematrixing means receiving from said coding, transmission, or storage and retrieval the signals from the adaptive 4:2 audio signal encoding for producing four audio signals representing the four audio source signals, the dematrixing means including 2:4 matrix decoding means and means for adaptively applying the received signals to said 2:4 matrix decoding means in a first state of operation and the sum and difference of the received signals to said 2:4 matrix decoding means in a second state of operation, and
• means receiving said control signal from said coding, transmission, or storage and retrieval for controlling said decode adaptive dematrixing means in response to said control signal, such that the decode adaptive dematrixing means operates in the first state when the adaptive matrix encoding is in the first state and operates in the second state when the adaptive matrix encoding is in the second state.

In a system in which the noise level varies with signal amplitude level, apparatus for adaptively rematrixing and 2:4 matrix decoding signals received from coding, transmission, or storage and retrieval in response to a control signal also received from the coding, transmission, or storage and retrieval, the received signals resulting from encoding of four audio source signals prior to application to said coding, transmission, or storage and retrieval by a 4:2 audio signal encoding matrix and adaptive rematrixing of the encoding matrix output signals such that in one state of the adaptive rematrixing the signals applied to the coding, transmission, or storage and retrieval are the output of the encoding matrix and in another state of the adaptive rematrixing the signals applied to the coder, transmission or storage are the amplitude weighted sum and difference of the output of the encoding matrix, said control signal indicating the state of the adaptive rematrixing, comprising

• decode adaptive rematrixing means receiving said encoding matrix output signals or the sum and difference of the encoding matrix output signals and said control signal from the coding, transmission, or storage and retrieval, said means recovering the received signals unaltered when said adaptive rematrixing means applied the matrix encoder output signals to the coding, transmission, or storage and retrieval and for recovering the sum and difference of the received signals when the adaptive rematrixing means applied the sum and difference of the matrix encoder output signals to the coding, transmission, or storage and retrieval, and
• complementary 2:4 audio decoding matrix means receiving the unaltered received signals or the sum and difference of the received signals for providing four matrix output signals representing the four audio signals applied to the 4:2 audio encoding matrix.

Apparatus for adaptively matrix decoding signals received from coding, transmission, or storage and retrieval in response to a control signal also received from the coding, transmission, or storage and retrieval, the received signals resulting from the adaptive audio 4:2 matrix encoding of four audio source signals L, C, R, and S such that the adaptive matrix encoding operates in a first state providing two matrix encoded audio signals L.sub.T and R.sub.T having characteristics such that

• L.sub.T =L+0.707C+0.707S,
• and
• R.sub.T =R+0.707C-0.707S
• when L.sub.T or R.sub.T had the smallest amplitude among L.sub.T, R.sub.T, k(L.sub.T +R.sub.T), and k(L.sub.T -R.sub.T), where k is a constant and the adaptive matrix encoding operates in a second state providing two matrix encoded audio signals L.sub.T ' and R.sub.T ' having characteristics such that ##EQU12## when L.sub.T ' or R.sub.T ' had the smallest amplitude among L.sub.T, R.sub.T, L.sub.T ' and R.sub.T ', the adaptive audio matrix encoding also producing a control signal indicating which set of relationships defined the output signals L.sub.T and R.sub.T or L.sub.T ' and R.sub.T ', comprising
• decode adaptive 2:4 audio matrix decoding means receiving said L.sub.T and R.sub.T or L.sub.T ' and R.sub.T ' signals from said coding, transmission, or storage and retrieval for providing four decoded signals L', C', R' and S' representative of the corresponding four audio source signals, the decode adaptive 2:4 audio matrix decoding means including 2:4 matrix decoding means and means for adaptively applying the received signals to said 2:4 matrix decoding means in a first state of operation and the sum and difference of the received signals to said 2:4 matrix decoding means in a second state of operation, and
• means receiving said control signal from said coding, transmission, or storage and retrieval for controlling said decode adaptive matrix decoding means in response to said control signal, such that the decode adaptive matrix decoding means operates in the first state when the adaptive matrix encoding is in the first state and operates in the second state when the adaptive matrix encoding is in the second state.

In a system in which the noise level varies with signal amplitude level, apparatus for use in a decoder complementary to an encoder in which audio signals are divided into frequency components and the frequency components are subject to bit-rate reduction encoding, the decoder receiving the output of the encoder via transmission or storage and retrieval, wherein the decoder bit-rate-reduction decodes and assembles decoded frequency components into representations of the audio signals applied to the encoder, the encoder receiving the two audio output signals of a 4:2 audio signal encoding matrix and the decoder applying decoded representations of the audio signals to a 2:4 audio signal decoding matrix, the encoder adaptively rematrixing frequency component representations of the 4:2 encoding matrix output signals such that in one state of the adaptive rematrixing the signals applied to the bit-rate reduction for transmission or storage are frequency components representations of the output of the encoding matrix and in another state of the adaptive rematrixing the signals applied to the bit-rate reduction encoding for transmission or storage are frequency component representations of the sum and difference of the output of the encoding matrix, said adaptive matrixing producing a control signal indicating the state of the adaptive rematrixing, comprising

• decode adaptive rematrixing means receiving from the decoder bit-rate reduction decoded frequency component representations of said 4:2 encoder matrix output signals unaltered or the sum and difference thereof for producing frequency components which are assembled by the decoder into representations of the audio signals applied to the encoder by the 4:2 encoding matrix, the decode adaptive rematrixing means having a first state with characteristics substantially the same as the first state of the adaptive matrix encoding and a second state with characteristics substantially the same as the second state of the adaptive matrix encoding, and
• means receiving said control signal from said transmission or storage and retrieval for controlling said decode adaptive rematrixing means in response to said control signal, such that the decode adaptive rematrixing means operates in said first state when the matrix encoder output signals are applied to the transmission or storage and retrieval and the decode adaptive rematrixing means operates in said second state when the sum and difference of the matrix encoder output signals are applied to the transmission or storage and retrieval.

In a system for coding, transmission, or storage and retrieval of audio signals received from a 4:2 audio signal encoding matrix and applied to a complementary 2:4 audio decoding matrix, the system having a noise level which varies with signal amplitude level, a method comprising

• determining which of the signals among the encoding matrix output signals and the sum and difference of the encoding matrix output signals has the smallest amplitude,
• applying the encoding matrix output signals to the coding, transmission, or storage and retrieval if one of the encoding matrix output signals has the smallest amplitude and applying the sum and difference of the encoding matrix output signals to the coding, transmission, or storage and retrieval if one of the sum and difference of the encoding matrix output signals has the smallest amplitude, and also applying a control signal to the coding, transmission, or storage and retrieval indicating if the encoding matrix output signals or the sum and difference of the encoding matrix output signals is being applied to the transmission or storage, and
• receiving said matrix output signals or the sum and difference of the matrix output signals, and said control signal from the coding, transmission, or storage and retrieval, and recovering unaltered, for use by the complementary 2:4 decoding matrix, the received signals when the matrix encoder output signals are applied to the coding, transmission, or storage and retrieval and recovering the sum and difference of the received signals, for use by the complementary 2:4 decoding matrix, when the sum and difference of the matrix encoder output signals are applied to the coding, transmission, or storage and retrieval.

In a system in which the noise level varies with signal amplitude level, a method for adaptively rematrixing signals received from coding, transmission, or storage and retrieval in response to a control signal also received from the coding, transmission, or storage and retrieval for applying the adaptively rematrixed signals to a 2:4 audio decoding matrix, the received signals resulting from encoding by a 4:2 audio signal encoding matrix and adaptive rematrixing of the encoding matrix output signals such that in one state of the adaptive rematrixing the signals applied to the coding, transmission, or storage and retrieval are the output of the encoding matrix and in another state of the adaptive rematrixing the signals applied to the coding, transmission, or storage and retrieval are the sum and difference of the output of the encoding matrix, said control signal indicating the state of the adaptive rematrixing, comprising

• receiving said matrix output signals or the sum and difference of the matrix output signals from the coding, transmission, or storage and retrieval and producing audio signals representing the output of said 4:2 encoding matrix for application to said 2:4 decoding matrix, recovering unaltered the matrix output signals from the coding, transmission, or storage and retrieval in a first state of operation and recovering the sum and difference of the matrix output signals from the coding, transmission, or storage and retrieval in a second state of operation, and
• receiving said control signal from said coding, transmission, or storage and retrieval and controlling the state of operation in response thereto such that when the matrix encoder output signals are applied to the coding, transmission, or storage and retrieval, the operation is in the first state and when the sum and difference of the matrix encoder output signals are applied to the coding, transmission, or storage and retrieval, the operation is in the second state.