# US 2014/0153744 A1 · Audio Precompensation Controller Design Using a Variable Set of Support Loudspeakers

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- Number: US 2014/0153744 A1
- Document ID: US20140153744A1
- Status: Published application
- Kind: A1
- Application number: 14/009,215
- Filed: 2012-03-22
- Published: 2014-06-05
- Earliest claimed: 2012-03-22
- Assignees: Dirac Research AB
- Inventors: Lars-Johan Brannmark; Anders Ahlen; Adrian Bahne
- Web page: https://patentgrep.com/patent/US20140153744A1

## CPC

- H04R 3/04: for correcting frequency response
- H04S 7/301: {Automatic calibration of stereophonic sound system, e.g. with test microphone}
- H04S 5/00: Pseudo-stereo systems, e.g. in which additional channel signals are derived from monophonic signals by means of phase shifting, time delay or reverberation
- H04S 7/305: {Electronic adaptation of stereophonic audio signals to reverberation of the listening space (H04S7/301 takes precedence)}
- H04R: LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS (producing sounds with frequency not determined by supply frequency G10K)
- H04S: STEREOPHONIC SYSTEMS

## Abstract

Disclosed is a method and a system to determine an audio precompensation controller for an associated sound generating system including a total of N≧2 loudspeakers, each having a loudspeaker input. The audio precompensation controller has a number L≧1 inputs for L input signals and N outputs for N controller output signals, one to each loudspeaker. For each one of at least a subset of the N loudspeaker inputs, an impulse response is estimated at each measurement position. For each one of the L input signal(s), a selected one of the N loudspeakers is specified as a primary loudspeaker and a selected subset S including at least one of the N loudspeakers as support loudspeaker(s).

## Claims

### Claim 1

A method for determining an audio precompensation controller for an associated sound generating system comprising a total of N>2 loudspeakers, each having a loudspeaker input, said audio precompensation controller having a number L>1 inputs for L input signal(s) and N outputs for N controller output signals, one to each loudspeaker of said sound generating system, said audio precompensation controller having a number of adjustable filter parameters, with said method comprising the steps of:
estimating, for each one of at least a subset of said N loudspeaker inputs, an impulse response at each of a plurality M>2 of measurement positions, distributed in a region of interest in a listening environment, based on sound measurements at said M measurement positions;
specifying, for each one of said L input signal(s), a selected one of said N loudspeakers as a primary loudspeaker and a selected subset S including at least one of said N loudspeakers as support loudspeaker(s), where said primary loudspeaker is not part of said subset;
specifying, for each primary loudspeaker, a target impulse response at each of said M measurement positions with said target impulse response having an acoustic propagation delay, where said acoustic propagation delay is determined based on the distance from the primary loudspeaker to the respective measurement position; and
determining, for each one of said L input signal(s), based on the selected primary loudspeaker and the selected support loudspeaker(s), filter parameters of said audio precompensation controller so that a criterion function is optimized under the constraint of stability of the dynamics of said audio precompensation controller, with said criterion function including a weighted summation of powers of differences between the compensated estimated impulse responses and the target impulse responses over said M measurement positions.

### Claim 2 (depends on 1)

The method of claim 1, wherein L>2, and said method comprises the step of merging all of said filter parameters, determined for said L input signals, into a merged set of filter parameters for said audio precompensation controller, wherein said audio precompensation controller with said merged set of filter parameters is configured for operating on said L input signals to generate said N controller output signals to said loudspeakers to attain said target impulse responses.

### Claim 3 (depends on 1)

The method of claim 1, wherein said audio precompensation controller is configured for controlling the acoustic response of P primary loudspeakers, where P<L and P≦N, by the combined use of said P primary loudspeakers and, for each primary loudspeaker, an additional number of support loudspeakers 1<S<N−1 of said N loudspeakers.

### Claim 4 (depends on 1)

The method of claim 1, wherein said audio precompensation controller has the ability of producing output zero to some of said N loudspeakers for some setting of its adjustable filter parameters.

### Claim 5 (depends on 1)

The method of claim 1, wherein said step of determining filter parameters of said audio precompensation controller is based on a Linear Quadratic Gaussian (LQG) optimization of the parameters of a stable, linear and causal multivariable feedforward controller based on a given target dynamical system, and a dynamical model of the sound generating system.

### Claim 6 (depends on 1)

The method of claim 1, wherein each one of said N controller output signals of said audio precompensation controller is fed to a respective loudspeaker via an all-pass filter including a phase compensation component and a delay component, yielding N filtered controller output signals.

### Claim 7 (depends on 1)

The method of claim 1, wherein said criterion function includes penalty terms, with said penalty terms being such that said audio precompensation controller, obtained by optimizing said criterion function, produces signal levels of constrained magnitude on a selected subset of said precompensation controller outputs, yielding constrained signal levels on selected loudspeaker inputs to said N loudspeakers for specified frequency bands.

### Claim 8 (depends on 7)

The method of claim 7, wherein said penalty terms are differently chosen a number of times and said step of determining filter parameters of said audio precompensation controller is repeated for each choice of said penalty terms, resulting in a number of instances of said audio precompensation controller, each of which produces signal levels with individually constrained magnitudes to said S support loudspeakers for specified frequency bands.

### Claim 9 (depends on 1)

The method of claim 1, wherein said criterion function includes, firstly, a set of models describing a range of possible errors in the estimated impulse responses, and secondly, an aggregation operation, where said aggregation operation is a sum, a weighted sum or a statistical expectation over said set of models.

### Claim 10 (depends on 1)

The method of claim 1, wherein said step of determining filter parameters of said audio precompensation controller is also based on adjusting filter parameters of said audio precompensation controller to reach a target magnitude frequency response of said sound generating system including said audio precompensation controller, in at least a subset of said M measurement positions.

### Claim 11 (depends on 10)

The method of claim 10, wherein said step of adjusting filter parameters of said audio precompensation controller is based on the evaluation of magnitude frequency responses in at least a subset of said M measurement positions and thereafter determining a minimum phase model of said sound generating system including said audio precompensation controller.

### Claim 12 (depends on 1)

The method of claim 1, where the target impulse responses are nonzero and include adjustable parameters that can be modified within prescribed limits.

### Claim 13 (depends on 12)

The method of claim 12, where the adjustable parameters of the target impulse responses, as well as the adjustable parameters of the audio precompensation controller, are adjusted jointly, with the aim of optimizing said criterion function.

### Claim 14 (depends on 1)

The method of claim 1, wherein said step of estimating, for each one of at least a subset of said N loudspeaker inputs, an impulse response at each of a plurality M of measurement positions is based on a model describing the dynamical response of said sound generating system at said M measurement positions.

### Claim 15 (depends on 1)

The method of claim 1, wherein said audio precompensation controller is created by implementing said filter parameters in an audio filter structure.

### Claim 16 (depends on 15)

The method of claim 15, wherein said audio filter structure is embodied together with said sound generating system to enable generation of said target impulse response at said M measurement positions in said listening environment.

### Claim 17 (depends on 1)

The method of claim 1, wherein said sound generating system is a car audio system or mobile studio audio system and said listening environment is part of a car or a mobile studio.

### Claim 18 (depends on 1)

The method of claim 1, wherein said sound generating system is a cinema theatre audio system, concert hall audio system, home audio system, or a professional audio system and said listening environment is part of a cinema theatre, a concert hall, a home, a studio, an auditorium, or any other premises.

### Claim 19

A system for determining an audio precompensation controller for an associated sound generating system comprising a total of N>2 loudspeakers, each having a loudspeaker input, said audio precompensation controller having a number L>1 inputs for L input signal(s) and N outputs for N controller output signals, one to each loudspeaker of said sound generating system, said audio precompensation controller having a number of adjustable filter parameters, with said system comprising:
means for estimating, for each one of at least a subset of said N loudspeaker inputs, an impulse response at each of a plurality M>2 of measurement positions, distributed in a region of interest in a listening environment, based on sound measurements at said M measurement positions;
means for specifying, for each one of said L input signal(s), a selected one of said N loudspeakers as a primary loudspeaker and a selected subset S including at least one of said N loudspeakers as support loudspeaker(s), where said primary loudspeaker is not part of said subset;
means for specifying, for each primary loudspeaker, a target impulse response at each of said M measurement positions with said target impulse response having an acoustic propagation delay, where said acoustic propagation delay is determined based on the distance from the primary loudspeaker to the respective measurement position; and
means for determining, for each one of said L input signal(s), based on the selected primary loudspeaker and the selected support loudspeaker(s), filter parameters of said audio precompensation controller so that a criterion function is optimized under the constraint of stability of the dynamics of said audio precompensation controller, with said criterion function including a weighted summation of powers of differences between the compensated estimated impulse responses and the target impulse responses over said M measurement positions.

### Claim 20 (depends on 19)

The system of claim 19, wherein L>2, and said system comprises means for merging all of said filter parameters, determined for said L controller input signals, into a merged set of filter parameters for said audio precompensation controller, wherein said audio precompensation controller with said merged set of filter parameters is configured for operating on said L input signals to generate said N controller output signals to said loudspeakers to attain said target impulse responses.

### Claim 21 (depends on 19)

The system of claim 19, wherein said means for determining filter parameters of said audio precompensation controller is configured to operate based on a Linear Quadratic Gaussian (LQG) optimization of the parameters of a stable, linear and causal multivariable feedforward controller based on a given target dynamical system, and a dynamical model of the sound generating system.

### Claim 22

A computer program product for determining, when running on a computer system, an audio precompensation controller for an associated sound generating system comprising a total of N>2 loudspeakers, each having a loudspeaker input, said audio precompensation controller having a number L>1 inputs for L input signal(s) and N outputs for N controller output signals, one to each loudspeaker of said sound generating system, said audio precompensation controller having a number of adjustable filter parameters, with said computer program product comprising:
program means for estimating, for each one of at least a subset of said N loudspeaker inputs, an impulse response at each of a plurality M>2 of measurement positions, distributed in a region of interest in a listening environment, based on sound measurements at said M measurement positions;
program means for specifying, for each one of said L input signal(s), a selected one of said N loudspeakers as a primary loudspeaker and a selected subset S including at least one of said N loudspeakers as support loudspeaker(s), where said primary loudspeaker is not part of said subset;
program means for specifying, for each primary loudspeaker, a target impulse response at each of said M measurement positions with said target impulse response having an acoustic propagation delay, where said acoustic propagation delay is determined based on the distance from the primary loudspeaker to the respective measurement position;
program means for determining, for each one of said L input signal(s), based on the selected primary loudspeaker and the selected support loudspeaker(s), filter parameters of said audio precompensation controller so that a criterion function is optimized under the constraint of stability of the dynamics of said audio precompensation controller, with said criterion function including a weighted summation of powers of differences between the compensated estimated impulse responses and the target impulse responses over said M measurement positions.

### Claim 23 (depends on 22)

The computer program product of claim 22, wherein L>2, and said computer program product comprises program means for merging all of said filter parameters, determined for said L input signals, into a merged set of filter parameters for said audio precompensation controller, wherein said audio precompensation controller with said merged set of filter parameters is configured for operating on said L input signals to generate said N controller output signals to said loudspeakers to attain said target impulse responses.

### Claim 24 (depends on 22)

The computer program product of claim 22, wherein said means for determining filter parameters of said audio precompensation controller is configured to operate based on a Linear Quadratic Gaussian (LQG) optimization of the parameters of a stable, linear and causal multivariable feedforward controller based on a given target dynamical system, and a dynamical model of the sound generating system.

### Claim 25 (depends on 1)

An audio precompensation controller determined by using the method of claim 1.

### Claim 26 (depends on 25)

The audio precompensation controller of claim 25, wherein said audio precompensation controller is a linear stable causal feedforward controller.

### Claim 27 (depends on 1)

An audio system comprising a sound generating system and an audio precompensation controller in the input path to said sound generating system, wherein said audio precompensation controller is determined by using the method of claim 1.

### Claim 28 (depends on 1)

A digital audio signal generated by an audio precompensation controller determined by using the method of claim 1.