Variable matrix decoder

• US 4,941,177 A
• Filed: 07/22/1988
• Issued: 07/10/1990
• Est. Priority Date: 03/07/1985
• Status: Expired due to Term

• Current Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Original Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Inventors: Mandell, Douglas E., Davis, Mark F., Allen, Ioan R., Todd, Craig C.
• Primary Examiner(s): Isen, Forester W.
• Application Number:
  US07/222,847
• Time in Patent Office: 718 Days
• Field of Search: 381/22, 381/21, 381/20, 381/19, 381/18
• US Class Current: 381/22
• CPC Class Codes: H04S 3/02 of the matrix type, i.e. in which input signals are combined algebraically, e.g. after having been phase shifted with respect to each other
• CPC Class Codes: H04S 5/005 of the pseudo five- or more-channel type, e.g. virtual surround

Abstract

The decoder of this invention decodes at least two channel signals in a directional information system where at least four input signals containing directional information have been encoded into the two or more channel signals. The decoder generates a first control signal substantially proportional to the logarithm of the ratio of the amplitudes of two of the channel signals to detect, as between two of the channel signals, whether the amplitude of one signal dominates that of the other. The decoder also generates a second control signal substantially proportional to the logarithm of the ratio of the amplitudes of the sum and the difference between two of the channel signals to detect the dominant signal in terms of amplitude. The decoder includes a matrix means responsive to the two or more channel signals and the two control signals for generating a number of output signals according to an algorithm. The control signals generated are used to steer the directional information systems in such manner through the matrix means that the directional effects of the output signals are enhanced. Two decoders of the type described above may be used to decode the high frequency and low frequency portions of the channel signals where the high and low frequency portions are separated by means of two crossover filters. The crossover frequency of the two crossover filters is controlled so that it is approximately at the top end of the signal frequencies intended for the center loudspeaker. Very low frequency signal components are separately processed and evenly distributed among the left, center and right channels.

Claims

1. A decoder for decoding two or more channel signals in a directional information system wherein at least four input signals containing directional information are encoded into the two or more channel signals, said decoder comprising:

first means for generating at least a first dominance signal indicative of the ratio of the amplitudes of a pair of the channel signals;

second means for generating at least a second dominance signal indicative of the ratio of the amplitudes of the sum of and the difference between said pair of the channel signals; and

matrix means responsive to said two or more channel signals and to said at least two dominance signals for generating a plurality of output signals for which directional effects of the output signals are enhanced, wherein the first dominance signal D_LR and the second dominance signal D_CS are given by;

##EQU11## where L_T, R_T are two channel signals

space="preserve" listing-type="equation">P=L.sub.T +R.sub.T, M=L.sub.T -R.sub.T ;

and a, k are constants;

wherein said matrix means includes means for deriving three directional control signals E_L, E_R and E_C.

2. The decoder of claim 1, wherein said means for deriving three directional control signals E_L, E_R, E_C derives the three directional control signals according to the following equations:

##EQU12##

3. The decoder of claim 2, wherein the matrix means generates the three outputs signals L'"'"', R'"'"', C'"'"', so that the three output signals are defined by means of the equations below:

##EQU13## where V is a 1 by 4 matrix;

G_L, G_R, G_C, are 4 by 2 matrices of predetermined coefficients;

b is a constant and

F_L, F_R, R_C, are given by;

F_L =a^b.E_L

F_R =a^b.E_R

F_C =a^b.E_C.

4. The decoder of claim 3, wherein the value of b is about 0.839.

5. The decoder of claim 3, wherein the G_L, G_R, G_C matrices are as follows:

##EQU14##

6. The decoder of claim 3, wherein the G_L, G_R, G_C matrices are derived from four equations Q×

G_L =H_L, Q×

G_R =H_R, Q×

G_C =H_C, where ##EQU15##

7. The decoder of claim 3, wherein the matrix means further comprises:

means for generating 6 product signals wherein each of the product signals is the product of either L_T lor R_T with one of 3 signals F_L, F_C, F_R ; and

means for adding weighted sums of the six product signals to obtain output signals L'"'"', C'"'"', R'"'"'.

8. The decoder of claim 7, wherein said product signals generating means includes six voltage controlled amplifiers for generating the six product signals.

9. The decoder of claim 3, wherein the matrix means further comprises:

means for generating the 3 signals F_L, F_C, F_R from E_L, E_R l, E_C l; and

means for performing the matrix multiplications V×

G_L, V×

G_R, V×

G_C.

10. The decoder of claim 1, further comprising a threshold detection means for detecting the amplitudes of the dominance signals, an averaging means and a switch, wherein the threshold detection means causes an average value of the dominance signals over a preceding time period to be applied to the matrix means upon detecting that the amplitudes of the dominance signals are below a predetermined threshold, so that the directional enhancements are determined by the average value of the dominance signals.

11. The decoder of claim 1, further comprising an averaging means for applying an average value of the dominance signals over a preceding time period to the matrix means, so that the directional enhancement of the output signals by the matrix means is in accordance with the average value.

12. The decoder of claim 11, wherein the averaging means has two different time constants, one time constant being operative when at least one dominance signal has an amplitude greater than a threshold value and the other time constant being operative when neither of the dominance signals have an amplitude above said threshold value.

13. The decoder of claim 12, wherein said averaging means comprises:

a variable resistor whose resistance varies inversely with the amplitudes of the dominance signals, said resistor connected between the first or second dominance signal generating means and the matrix means; and

an impedance means forming a low pass filter configuration with the resistor.

14. The decoder of claim 12, wherein said impedance means comprises:

a first and a second capacitor means connected in series between ground and a first point in the connection between the variable resistor and the matrix means;

a first resistor means forming a charge path for the first capacitor means, the first capacitor means having a capacitance much smaller than that of the second capacitor means so that the voltage across the first capacitor means responds more quickly than that across the second capacitor means to changes in the amplitudes of the dominance signals, so that when dominance signals increase in amplitudes, the averaging means will respond mainly to the voltage across the first capacitor means, thereby enabling the decoder to use the dominance signals to steer the decoder.

15. The decoder of claim 14, said decoder further comprising means for discharging the second capacitor means so that when the amplitudes of both dominance signals decrease to substantially zero, the first capacitor means is discharged through the first resistor means in a much shorter time than the second capacitor means, so that the directional enhancement of the output signals by the matrix means is substantially determined by the voltage across the second capacitor means before the second capacitor means has been discharged, and so that no directional enhancement is applied when the second capacitor means has been substantially discharged.

16. The decoder of claim 13, wherein said variable resistor is a transconductance amplifier.

17. A method for decoding two or more channel signals using a directional information system wherein at least four input signals containing directional information have been encoded into the two or more channel signals, said method comprising:

generating at least a first dominance signal indicative of the ratio of the amplitudes of a pair of the channel signals;

generating at least a second dominance signal indicative of the ratio of the amplitudes of the sum of and the difference between said pair of the channel signals; and

generating a plurality of output signals for which directional effects of the output signals are enhanced in response to said two or more channel signals and to said at least two dominance signals, wherein the first dominance signal D_LR and the second dominance signals D_CS are given by ##EQU16## where L_T, R_T are two channel signals

space="preserve" listing-type="equation">P=L.sub.T +R.sub.T, M=L.sub.T -R.sub.T ;

and a, k are constants.

wherein said output signals generating step includes deriving three directional control signals E_L, E_R, E_C.

18. The method of claim 17, wherein said output signals generating step derives the control signals E_L, E_R, E_C according to the following equations:

##EQU17##

19. The method of claim 18, wherein the output signals generating step generates the three output signals L'"'"', R'"'"', C'"'"', so that the three output signals are defined by means of the equations below:

##EQU18## where V is a 1 by 4 matrix;

G_L, G_R, are 4 by 2 matrices of predetermined coefficients;

b is a constant and

F_L, F_R, F_C are given by;

##EQU19##

20. The method of claim 19, wherein the G_L, G_R, G_C matrices are as follows:

##EQU20##

21. The method of claim 19, further comprising the step of deriving the G_L, G_R, G_C matrices from four equations Q×

G_L =H_L, Q×

G_R =H_R, Q×

G_C =H_C, where ##EQU21##

22. The method of claim 19, wherein the output signals generating step further comprises:

generating 6 product signals wherein each of the product signals is the product of either L_T or R_T with one of 3 signals F_L, F_C, F_R ; and

adding weighted sums of the six product signals to obtain output signals L'"'"', C'"'"', R'"'"'.

23. The method of claim 19, wherein the output signals generating step further comprises:

generating the 3 signals F_L, F_C, F_R from E_L, E_R, E_C ; and

performing the matrix multiplications V×

G_L, V×

G_R ;

V×

G_C.

24. A decoder for decoding two or more channel signals in a directional information system wherein at least four input signals containing directional information are encoded into the two or more channel signals, said decoder comprising:

first means for generating at least a first dominance signal indicative of the ratio of the amplitudes of the sum of and the difference between said pair of the channel signals; and

matrix means responsible to said two or more channel signals and to said at least two dominance signals for generating a plurality of output signals for which directional effects of the output signals are enhanced, wherein the first dominance signal D_LR and the second dominance signal D_CS are given by;

##EQU22## where L_T, R_T are two channel signals

space="preserve" listing-type="equation">P=L.sub.T +R.sub.T, M=L.sub.T -R.sub.T ;

and a is a constant,

and wherein said matrix means includes means for deriving four directional control signals E_L, E_R, E_C, E_S according to the following equations;

##EQU23##

25. The decoder of claim 24, further comprising a threshold detection means for detecting the amplitudes of the dominance signals, an averaging means and a switch, wherein the threshold detection means causes an average value of the dominance signals over a preceding time period to be applied to the matrix means upon detecting that the amplitudes of the dominance signals are below a predetermined threshold, so that the directional enhancements are determined by the average value of the doninance signals.

26. The decoder of claim 24, wherein the directional control signals deriving means derives the four output signals L'"'"', R'"'"', C'"'"', S'"'"', so that the four signals are defined by means of the equations below:

##EQU24## where V is a 1 by 5 matrix;

G_L, G_R, G_C, G_S are 5 by 2 matrices of predetermined coefficients;

b is a constant and

F_L, F_R, F_C, F_S are given by;

##EQU25##

27. The decoder of claim 26, wherein the value of b is about 0.839.

28. The decoder of claim 26, wherein the G_L, G_R, G_C, G_S matrices are as follows:

##EQU26##

29. The decoder of claim 26, wherein the G_L, G_R, G_C, G_S matrices are derived from four equations Q×

G_L =H_L, Q×

G_R =H_R, Q×

G_C =H_C, Q×

G_S =H_S, where ##EQU27##

30. The decoder of claim 26, wherein the matrix means further comprises:

means for generating 8 product signals wherein each of the signals is the product of either L_T or R_T with one of 4 signals F_L, F_C, F_R, F_S ; and

means for adding weighted sums of the eight product signals to obtain output signals L'"'"', C'"'"', R'"'"', S'"'"'.

31. The decoder of claim 30, wherein said product signals generating means includes eight voltage controlled amplifiers for generating the eight product signals.

32. The decoder of claim 26, wherein the matrix means further comprises:

means for generating the 4 signals F_L, F_C, F_R, F_S from E_L, E_R, E_C, E_S ; and

means for performing the matrix multiplications V×

G_L, V×

G_R, V×

G_C, V×

G_S.

33. The decoder of claim 24, further comprising an averaging means for applying an average value of the dominance signals over a preceding time period to the matrix means, so that the directional enhancement of the output signals by the matrix means is in accordance with the average value.

34. The decoder of claim 33, wherein the averaging means has two different time constants, one time constant being operative when at least one dominance signal has an amplitude greater than a threshold value and the other time constant being operative when neither of the dominance signals have an amplitude above said threshold value.

35. The decoder of claim 34, wherein said averaging means comprises:

a variable resistor whose resistance varies inversely with the amplitudes of the dominance signals, said resistor connected between the first or second dominance signal generating means and the matrix means; and

an impedance means forming a low pass filter configuration with the resistor.

36. The decoder of claim 34, wherein said impedance means comprises:

a first and a second capacitor means connected in series between ground and a first point in the connection between the variable resistor and the matrix means;

a first resistor means forming a charge path for the first capacitor means, the first capacitor means having a capacitance much smaller than that of the second capacitor means so that the voltage across the first capacitor means responds more quickly than that across the second capacitor means to changes in the amplitudes of the dominance signals, so that when dominance signals increase in amplitudes, the averaging means will respond mainly to the voltage across the first capacitor means, thereby enabling the decoder to use the dominance signals to steer the decoder.

37. The decoder of claim 36, said decoder further comprising means for discharging the second capacitor means so that when the amplitudes of both dominance signals decrease to substantially zero, the first capacitor means is discharged through the first resistor means in a much shorter time than the second capacitor means, so that the directional enhancement of the output signals by the matrix means is substantially determined by the voltage across the second capacitor means before the second capacitor means has been discharged, and so that no directional enhancement is applied when the second capacitor means has been substantially discharged.

38. The decoder of claim 35, wherein said variable resistor is a transconductance amplifier.