Source: http://www.google.com/patents/US5291557?dq=5,666,293
Timestamp: 2013-12-05 09:01:50
Document Index: 26052352

Matched Legal Cases: ['art 3', 'art 3', 'art.5', 'art 3', 'art 3', 'art.7']

Patent US5291557 - Adaptive rematrixing of matrixed audio signals - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Advanced Patent Search | Sign inAdvanced Patent SearchPatentsIn a system in which a low-bit rate encoder and decoder carries matrixed audio signals, an adaptive rematrix rematrixes matrixed signals from an unmodified 4:2 matrix encoder to separate and isolate quiet components from loud ones, thereby avoiding the corruption of quiet signals with the low-bit-rate...http://www.google.com/patents/US5291557?utm_source=gb-gplus-sharePatent US5291557 - Adaptive rematrixing of matrixed audio signalsPublication numberUS5291557 APublication typeGrantApplication numberUS 07/959,730Publication dateMar 1, 1994Filing dateOct 13, 1992Priority dateOct 13, 1992Fee statusPaidAlso published asCA2142092A1, CA2142092C, DE69311569D1, DE69311569T2, EP0664943A1, EP0664943B1, WO1994009608A1Publication number07959730, 959730, US 5291557 A, US 5291557A, US-A-5291557, US5291557 A, US5291557AInventorsMark F. Davis, Stephen D. VernonOriginal AssigneeDolby Laboratories Licensing CorporationPatent Citations (3), Non-Patent Citations (14), Referenced by (32), Classifications (6), Legal Events (6) External Links: USPTO, USPTO Assignment, EspacenetAdaptive rematrixing of matrixed audio signalsUS 5291557 AAbstract In a system in which a low-bit rate encoder and decoder carries matrixed audio signals, an adaptive rematrix rematrixes matrixed signals from an unmodified 4:2 matrix encoder to separate and isolate quiet components from loud ones, thereby avoiding the corruption of quiet signals with the low-bit-rate coding quantization noise of loud signals. The decoder is similarly equipped with a rematrix, which tracks the encoder rematrix and restores the signals to the form required by the unmodified 2:4 matrix decoder. The encoder adaptive rematrix selects the matrix output signals or the amplitude weighted sum and difference of the matrix output signals. The choice of whether the matrix output signals or the sum and difference of the matrix output signals are selected is based on a determination of which results in fewer undesirable artifacts when the output audio signals are recovered in the decoder. The adaptive rematrix may operate on frequency component representations of signals rather than the time-domain signals themselves.
6. An adaptive audio encoding matrix, comprising4:2 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. 7. Apparatus for use in an encoder for a signal transmission or storage and retrieval system in which audio signals in the encoder are represented as frequency components and the frequency components are subject to bit-rate reduction encoding, the encoder having a noise level which varies with signal amplitude level, the encoder receiving the audio output signals of a 4:2 audio signal matrix, the apparatus adaptively rematrixing frequency component representations of the 4:2 matrix output signals, comprisingmeans 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 means for applying the frequency component representations of the matrix output signals to the bit-rate reduction encoding if one of the matrix output signals has the smallest amplitude and for applying the sum and difference of the matrix output signals to the bit-rate reduction encoding if one of the sum difference of the matrix output signals has the smallest amplitude. 8. The apparatus of claim 7 wherein the sum of the matrix output signals is an amplitude weighted sum and the difference of the matrix output signals is an amplitude weighted difference.
18. The apparatus of claim 3 or 11 wherein said 4:2 audio matrix means provides two output signals in response to four input signals generally in accordance with the relationships L.sub.T =L+0.707C+0.707S, and R.sub.T =R+0.707C-0.707S where, L is Left channel signal, R is the Right channel signal, C is the Center channel signal and S is the Surround channel signal. 19. The apparatus of claim 3 or 11 wherein the combined action of said 4:2 audio matrix means and said adaptive rematrixing 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 ##EQU6## 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 ' where, L is Left channel signal, R is the Right channel signal, C is the Center channel signal, S is the Surround channel signal and k is a constant. 20. 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 comprisingmeans 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. 21. The apparatus of claim 20 wherein the sum of the encoding matrix output signals is an amplitude weighted sum and the difference of the encoding matrix output signals is an amplitude weighted difference.
24. The apparatus of claim 22 wherein said 4:2 audio matrix means provides two output signals in response to four input signals generally in accordance with the relationships L.sub.T =L+0.707C+0.707S, and R.sub.T =R+0.707C-0.707S where, L is Left channel signal, R is the Right channel signal, C is the Center channel signal and S is the Surround channel signal and said complementary 2:4 audio decoding matrix means provides four output signals in response to two input signals generally in accordance with the relationships ##EQU7## 25. The apparatus of claim 22 wherein the combined action of said 4:2 audio matrix means and said adaptive rematrixing means provides as its output two signals L.sub.T and R.sub.T generally in accordance with a first set of 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 a second set of relationships ##EQU8## 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 ', where L, C, R, and S are the four audio signals received by the encoding matrix means, and wherein the combined action of said decode adaptive rematrixing means and said complementary 2:4 audio decoding matrix means provides as its output four signals L', C', R', S' representing the four audio signals applied to the 4:2 audio matrix encoding means generally in accordance with the relationships ##EQU9## when the control signal indicates that the adaptive encoding matrixing encoded the L.sub.T and R.sub.T signals in accordance with said first state of relationships, and wherein the second state of said adaptive 2:4 audio matrix decoding means provides as its output four signals L', C', R', S' representing the four audio signals applied to the 4:2 audio matrix encoding means generally in accordance with the relationships ##EQU10## when the control signal indicates that the adaptive encoding matrix encoded L.sub.T ' and L.sub.T ' in accordance with said second state of relationships, where the subscript D indicates decoded values of the respective signals. 26. An adaptive audio encoding and decoding matrix system for use with signal coding, transmission, or storage and retrieval, comprisingadaptive 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. 27. 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, comprisingadaptive 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. 28. The apparatus of claim 27 wherein the sum of the encoding matrix output signals is an amplitude weighted sum and the difference of the encoding matrix output signals is an amplitude weighted difference.
35. 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. 36. The apparatus of claim 35 wherein said adaptive 2:4 audio matrix decoding means provides as its output four signals L', C', R', S' representing the four audio signals applied to the 4:2 adaptive audio matrixing generally in accordance with the relationships ##EQU13##
L.sub.T =L+0.707C+0.707S                                   (Eqn. 1)
R.sub.T =R+0.707C-0.707S                                   (Eqn. 2)
where L is the Left channel signal, R is the Right channel signal, C is the Center channel signal and S is the Surround channel signal. Thus, the matrix encoder output signals are weighted sums of the four source signals. L.sub.T and R.sub.T are the matrix output signals.
The MP 2:4 decode matrix is defined by the following relationships: ##EQU1## where L' represents the decoded Left channel signal, R' represents the decoded Right channel signal, C' represents the decoded Center channel signal and S' represents the decoded Surround channel signal. Thus, the matrix decoder forms its output signals from weighted sums of the 4:2 encoder matrix output signals L.sub.T and R.sub.T.
As one example of this problem, assume that a 100 dB SPL (sound pressure level) signal is applied to the Center input channel of an MP matrix encoder with no signals (0 dB SPL) applied to the Left, Right or Surround inputs. In accordance with Equations 1 and 2, the encoder applies this signal equally to its L.sub.T and R.sub.T outputs, attenuated 3 dB, resulting in L.sub.T and R.sub.T signals at an equivalent level of 97 dB SPL. Assume further that a low-bit-rate encoder processing these signals has an instantaneous signal-to-noise ratio (SNR) of 30 dB. The 97 dB L.sub.T and R.sub.T correlated signals will each acquire 97-30=67 dB of uncorrelated noise. This uncorrelated noise will be masked in each of the MP matrix decoded Left, Center and Right channels by the respective 97 dB signals. However, when the MP matrix decoder reconstructs the Surround channel by subtracting R.sub.T from L.sub.T, the 97 dB correlated signal components cancel but the 67 dB noise components add because they are uncorrelated, resulting in 67 dB SPL of noise in the Surround channel with no signal to mask the noise.
In the preferred embodiment, the identity matrix form of the encode adaptive matrix applies L.sub.T and R.sub.T as shown in Equations 1 and 2, while the alternate sum/difference matrix form of the encode adaptive matrix applies a weighted sum L.sub.T '=1/2(L.sub.T +R.sub.T) in lieu of L.sub.T and a weighted difference R.sub.T '=1/2(L.sub.T -R.sub.T) in lieu of R.sub.T. The controller portion of the encode adaptive matrix selects either the identity matrix or the alternate matrix based on the amplitudes of L.sub.T, R.sub.T, L.sub.T ' and R.sub.T '.
The combined action of a 4:2 MP encode matrix and the adaptive rematrix thus provides either the standard MP matrix encoder outputs L.sub.T and R.sub.T as given by Equations 1 and 2 or alternate outputs L.sub.T ' and R.sub.T ' given by the relationships:
L.sub.T '=1/2(L.sub.T +R.sub.T)=1/2(L+R)+0.707C            (Eqn. 7)
R.sub.T '=1/2(L.sub.T -R.sub.T)=1/2(L-R)+0.707S            (Eqn. 8)
The 0.5 weighting shown in Equations 7 and 8 may be varied so long as the combined effect of the encode adaptive rematrix and the decode adaptive rematrix is substantially that of an identity matrix. Thus, equations 7 and 8 may be expressed more generally as: ##EQU3## where "k.sub.1 " is a constant subject to the aforementioned constraints.
The adaptive rematrix in the encoder and the adaptive rematrix in the decoder function essentially in the same way at the same time. They differ from each other only in the amplitude weighting or scaling applied to their respective output signals and in that the encoder adaptive rematrix has a controller. Because they operate together as part of a system, the way in which the amplitude weighting or scaling is apportioned between the encode rematrix and the decode rematrix is arbitrary so long as the output of the decode rematrix remains substantially unchanged as the encode and decode rematrix track with each other in switching between their two states. The combination of the encode rematrix and the decode rematrix is an identity matrix for both modes of operation. Thus, although in the preferred embodiment disclosed the encode and decode rematrices have amplitude scalings of 0.5 and 1.0, these weightings may be varied so long as the combination of the encode and decode rematrix remains substantially an identity matrix. It should be noted that the L.sub.T ' and R.sub.T ' values applied to the four-way controller in the encode rematrix should incorporate the amplitude scaling employed in the encode rematrix.
Taken in isolation, the combined action of the decode adaptive rematrix and the standard 2:4 MP matrix decoder provide either the standard MP matrix decoder output as given by Equations 3 though 6 (but replacing "L.sub.T " with "(L.sub.T).sub.D " and "R.sub.T " with (R.sub.T).sub.D in each instance in order to indicate that the terms are decoded representations of the signals) or an alternate output given by the relationships: ##EQU4## where (L.sub.T ').sub.D and (R.sub.T ').sub.D are the two alternate outputs resulting from the combination of 4:2 MP encode matrix and the encode adaptive rematrix defined by Equations 7 and 8. The subscript D indicates that these are the decoded values of L.sub.T ' and R.sub.T '. Under these conditions, the outputs of the adaptive rematrix 26 are (L.sub.T ').sub.D +(R.sub.T ').sub.D and (L.sub.T ').sub.D -(R.sub.T ').sub.D, respectively. The alternate decode matrix output given by Equations 9 through 12 is a 90 degree rotation of the standard MP decode matrix output given by Equations 3 through 6.
The 1.0 weighting of the alternate adaptive rematrix output may be varied so long as the combined effect of the encode adaptive rematrix and the decode adaptive rematrix is substantially that of an identity matrix. Thus, the outputs of the adaptive rematrix in its alternate sum/difference form may be expressed more generally as k.sub.2 [(L.sub.T ').sub.D +(R.sub.T ').sub.D ] and k.sub.2 [(L.sub.T ').sub.D -(R.sub.T ').sub.D ], respectively, where "k.sub.2 " is a constant subject to the aforementioned constraints.
If the weighted values of L, R, C and S corresponding to L.sub.T ' and R.sub.T ' in Equations 7 and 8 are substituted for (L.sub.T ').sub.D and (R.sub.T ').sub.D in equations 9 through 12, the output of the 2:4 MP matrix decoder is the same as in equations 3 through 6. Thus, under both modes of operation the 2:4 matrix decoder desired signal components remains the same, however, undesired noise components are reduced in the manner of the example set forth below.
In explaining the problem addressed by the invention, a specific example is given above in which 67 dB of noise results in the Surround channel output from the 2:4 MP decode matrix. In the example, the signal applied to the Center channel is 100 dB. Thus, applying teachings of the invention, L.sub.T and R.sub.T are each 97 dB, L.sub.T '=1/2(L.sub.T +R.sub.T)=97 dB and R.sub.T '=1/2(L.sub.T -R.sub.T)=-∞ dB (i.e. zero) and of the four signals L.sub.T, R.sub.T, L.sub.T ' and R.sub.T ', the smallest is the difference signal (R.sub.T ') which results in selection of the alternate matrix by the adaptive rematrix.
Selecting the alternate matrix as the adaptive rematrix causes L.sub.T '=1/2(L.sub.T +R.sub.T) and R.sub.T '=1/2(L.sub.T -R.sub.T) to be sent instead of L.sub.T and R.sub.T, respectively. Thus, the 97 dB L.sub.T and R.sub.T signals are converted to a 97 dB sum signal (L.sub.T ') and a -∞ dB (i.e., zero) difference signal (R.sub.T '). The 97 dB sum signal (L.sub.T ') will still pick up 67 dB of noise, while the zero amplitude difference signal picks up no noise. The decode adaptive rematrix reconstructs (L.sub.T ').sub.D +(R.sub.T ').sub.D and (L.sub.T ').sub.D -(R.sub.T ').sub.D from (L.sub.T ').sub.D and (R.sub.T ').sub.D, resulting in two 97 dB signals, each with 67 dB of noise, output from the adaptive rematrix to the 2:4 decode matrix. However, in this case the noise in each of the signals is identical instead of being uncorrelated. Consequently, when the 2:4 MP matrix decoder reconstructs the Surround channel by subtracting the two signals, the 97 dB signal components will cancel and so will the 67 dB noise components, resulting in -∞ dB SPL (i.e., no noise or signal) from the Surround channel, a useful improvement.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIGS. 1A and 1B of the drawings, encoding and decoding arrangements embodying various aspects of the invention are shown. The embodiments of FIGS. 1A and 1B are time-domain embodiments of the invention. The invention may also be expressed in frequency-domain embodiments, described below. In FIG. 1A, four audio signal source inputs L, C, R and S representing the Left, Center, Right and Surround sound channel inputs are shown applied to a 4:2 encoder matrix 2 which produces two output signals L.sub.T and R.sub.T which are weighted sums of the four source signals. The matrix preferably encodes the signals according to the MP encode matrix equations, Equations 1 and 2. The 4:2 matrix 2 may operate either in the analog domain or digital domain or some combination thereof. If it operates wholly or partially in the digital domain, the input and output signals may be parallel as suggested by the drawing or, alternatively, serially multiplexed.
The L.sub.T and R.sub.T encode matrix output signals are applied to an adaptive matrix 4. In some instances, the encode matrix 2 may be widely separated from the adaptive rematrix 4 temporally and/or spatially. For example, the four source signals may have been MP matrix encoded onto the SVA soundtracks of a motion picture many years before they are applied to the adaptive rematrix 4. The adaptive rematrix takes one of two forms: an identity, no change matrix and a sum/difference matrix. Thus, the outputs A and B from the adaptive rematrix 4 are either L.sub.T and R.sub.T from the identity matrix as shown in Equations 1 and 2 or L.sub.T '=1/2(L.sub.T +R.sub.T) in lieu of L.sub.T and R.sub.T '=1/2(L.sub.T -R.sub.T) in lieu of R.sub.T from the alternate sum/difference matrix. A control signal on line 6 indicates which form of the rematrix is in use.
Functional details of the encode adaptive rematrix 4 including its controller are shown in the block diagram of FIG. 2. The L.sub.T and R.sub.T input signals are applied to an alternate matrix 8 and to one pair of input poles of a double-pole double-throw switch 10. The alternate matrix 8 provides as its outputs the weighted sum and weighted difference of its inputs, namely L.sub.T '=1/2(L.sub.T +R.sub.T) and R.sub.T '=1/2(L.sub.T -R.sub.T). The L.sub.T and R.sub.T input signals and the L.sub.T ' and R.sub.T ' alternate matrix output signals are applied to a four-way amplitude comparator 12. Comparator 12 compares the amplitudes, preferably the RMS amplitudes, of L.sub.T, R.sub.T, L.sub.T ' and notes which is smallest. The signals may be frequency weighted. If the amplitude of L.sub.T or R.sub.T is smallest, the comparator 12, via line 14, causes switch 10 to select the identity matrix (i.e., the L.sub.T and R.sub.T inputs), else the comparator causes switch 10 to select the alternate matrix (i.e., the L.sub.T ' and R.sub.T ' inputs). The comparator 12 may choose the identity matrix or the alternate matrix periodically or aperiodically. The choice may, for example, be made in accordance with characteristics of the input signals L.sub.T and R.sub.T, at regular intervals, and/or in accordance with the encoding operations of an encoder associated with the adaptive rematrix. In the preferred embodiment described hereinafter, audio signals are divided into blocks by an encoder and the state of the adaptive rematrix is chosen for each block.
Referring now to the decoder arrangement of FIG. 1B, input 20 receives the encoded audio signals A and B and the control signal from a transmission channel or a storage and retrieval channel. A decoder 22, similar to the encoder 16, provides audio output signals (A).sub.D and (B).sub.D and, on line 24, the control signal. The subscripts indicated that these are decoded audio signals which may have suffered some degradation by transmission or storage and retrieval. (A).sub.D and (B).sub.D may be either (L.sub.T).sub.D and (R.sub.T).sub.D or (L.sub.T ').sub.D and (R.sub.T ').sub.D, respectively, depending on the form of the encode rematrix.
The decoded audio signals, (A).sub.D and (B).sub.D, and the control signal are applied to a decode adaptive rematrix 26. The decode adaptive rematrix reconstructs the two channels and provides either its inputs (L.sub.T).sub.D and (R.sub.T).sub.D or the sum and difference of its inputs (L.sub.T ').sub.D +(R.sub.T ').sub.D and (L.sub.T ').sub.D -(R.sub.T ').sub.D if the control signal indicates that the alternate matrix bit is selected.
As in FIG. 1A, four audio signal source inputs L, C, R and S representing the Left, Center, Right and Surround sound channel inputs are applied to a 4:2 encoder matrix 2 which produces two output signals L.sub.T and R.sub.T which are weighted sums of the four source signals. The matrix preferably encodes the signals according to the MP encode matrix equations, Equations 1 and 2. The 4:2 matrix 2 may operate either in the analog domain or digital domain or some combination thereof.
The L.sub.T and R.sub.T outputs of encode matrix 2 are applied to respective buffers 30 and 32. In some instances, the encode matrix 2 may be widely separated temporally and/or spatially from the buffers 30 and 32 and the subsequent blocks in FIG. 3A. Blocks 30 and 32 and the subsequent blocks in FIG. 3A operate in the digital domain. Thus, if the L.sub.T and R.sub.T signals from encode matrix 2 are analog, they must be converted to digital form by suitable means (not shown) prior to application to blocks 30 and 32. In the preferred embodiment, the digital form is 16- or more bit linear PCM and the PCM input signals in the time domain are divided into blocks and windowed along with buffering in blocks 30 and 32. As is well known in the art, windowing of the time-domain blocks is required when certain transforms are employed.
The encode adaptive rematrix 38 receives, via lines 35 and 37, the frequency component representations of the L.sub.T and R.sub.T signals and provides either the same frequency components, (L.sub.T).sub.f and (R.sub.T).sub.f, at its output or the weighted sum and difference thereof, (L.sub.T ').sub.f =1/2(L.sub.T +R.sub.T).sub.f and (R.sub.T ').sub.f =1/2(L.sub.T -R.sub.T).sub.f in a manner similar to adaptive rematrix 4 of FIG. 1A. The "f" subscript indicates that the signal is a frequency component representation.
The signals on lines 74 and 76 and the control signal are applied to the decode adaptive rematrix 78. The adaptive rematrix reconstructs the frequency components representing the two channels and provides either its inputs [(L.sub.T).sub.f ].sub.D and [(R.sub.T).sub.f ].sub.D or the sum and difference of its inputs [(L.sub.T ').sub.f ].sub.D +[(R.sub.T ').sub.f ].sub.D and [(L.sub.T ').sub.f ].sub.D -[(R.sub.T ').sub.f ].sub.D if the control signal indicates that the alternate matrix bit is selected.
The audio signal frequency component outputs from the adaptive rematrix 78 are applied via lines 80 and 82 to respective inverse transforms 84 and 86 to transform the frequency components into time-domain signals. In the preferred embodiment in which the encoding arrangement overlaps and windows blocks of buffered input signals, the decoding arrangement has overlap-add and window blocks 92 and 94 receiving the outputs of the inverse transforms via lines 88 and 90. The optional blocks 92 and 94 window, overlap and add adjacent sample blocks to cancel the weighting effects of the encoding analysis window and the decoding synthesis window. Blocks 92 and 94 provide the L.sub.T ' and R.sub.T ' signals on lines 96 and 98 to the 2:4 decode matrix 28 which provides the four audio signal outputs L', C', R' and S'. The prime marks indicate that the four signals representative of the original source signals L, C, R and S are not precisely the same due to inherent shortcomings of 4:2:4 audio matrices and also due to possible degradation of the two-channel signal during transmission or storage and retrieval.
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U.S. Classification381/22, 381/23International ClassificationH05H5/00, H04S3/02Cooperative ClassificationH04S3/02European ClassificationH04S3/02Legal EventsDateCodeEventDescriptionAug 17, 2005FPAYFee paymentYear of fee payment: 12Aug 16, 2001FPAYFee paymentYear of fee payment: 8Aug 21, 1997FPAYFee paymentYear of fee payment: 4Dec 10, 1996CCCertificate of correctionOct 13, 1992ASAssignmentOwner name: DOLBY LABORATORIES LICENSING CORPORATION, CALIFORNFree format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:DAVIS, MARK FRANKLIN;REEL/FRAME:006361/0478Effective date: 19921012Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:VERNON, STEPHEN D.;REEL/FRAME:006361/0482Oct 13, 1992AS02Assignment of assignor's interestOwner name: DOLBY LABORATORIES LICENSING CORPORATION 100 POTREOwner name: VERNON, STEPHEN D.Effective date: 19921012RotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided 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