HK1175628B - Multichannel audio system having audio channel compensation - Google Patents

Description

Multi-channel audio system with audio channel compensation

Priority declaration

This application claims the benefit of priority from U.S. provisional application No. 61/248,760 filed on 5.10.2009, the contents of which are incorporated herein by reference.

Technical Field

The present invention relates to multi-channel audio systems, and, more particularly, to audio channel compensation systems for multi-channel audio systems.

Background

The perception of sound provided by an audio system in the ambient environment may be degraded by reflective surfaces in the ambient environment. In such an ambient environment, both the original sound and a delayed version of the sound are presented to the listener, resulting in constructive interference and destructive interference. Such interference may produce deviations in the target frequency response, such as comb filtering effects. The frequency response of the comb filter includes a series of regularly spaced peaks and valleys, resulting in a comb-like shape. The sound received by the listener has a different frequency response than the desired sound originally emitted by the sound system.

Deviations in the target frequency response, such as comb filtering, may be particularly pronounced in substantially closed environments, such as the passenger compartment of a vehicle having a multi-channel audio sound system. Each listener in the car receives both direct and reflected sounds associated with each channel, resulting in a bias in the mutual influence of, for example, complex comb filtering, reducing the enjoyment of the listening experience.

Disclosure of Invention

The multi-channel compensating audio system may use one or more compensation channels to correct for deviations in target response at one or more listening positions within a listening area. Each of the one or more compensation channels may include a delay circuit, a level adjuster circuit, and a frequency equalizer circuit connected in series that generate a compensated audio signal from an audio signal on a channel of an input audio signal.

A multi-channel compensated audio system may drive a plurality of loudspeakers with corresponding audio signals provided by a sound source as a multi-channel audio input signal. For example, a 5.1 channel input audio signal may drive center, front right, front left, rear right, and rear left speakers with corresponding audio signals provided on center, front right, front left, rear right, and rear left audio channels. Each of the one or more compensation channels may receive and process an audio signal to generate a compensated audio signal.

In the case of first and second channels, and corresponding first and second speakers, a listener at a listening position may psychoacoustically perceive a deviation in a target frequency response caused by first speaker output through an audio signal on the first channel. In this case, the compensation channel may generate a compensated audio signal from the first audio signal supplied to the first speaker on the first channel based on a predetermined delay, a predetermined energy level adjustment, and/or a predetermined Equalization (EQ). The compensated audio signal may be electrically summed with a second audio signal supplied to a second speaker on a second channel. When the first and second speakers are operated in a listening space, a first audio signal output from the first speaker may be heard at a listening position in the listening space, and a listener at the listening position may perceptually position the origin of the first audio signal, e.g., from a first loudspeaker. When the sum of the compensated audio signal and the second audio signal is output from the second speaker, the listener may psychoacoustically perceive a correction for the deviation in the target response caused by the first speaker. However, due to the multi-channel compensated audio system, the listener cannot psychoacoustically perceive a change in the originating position of the first audio signal at the listening position.

Another interesting feature of the multi-channel compensated audio system may include equalizing the loudness of the sounds emanating from the different speakers, as psychoacoustically perceived at many different listening positions in the listening space. Using the audio channels and the compensated audio signals selectively produced by the different speakers, listeners at different listening positions may psychoacoustically perceive the spectral energy levels produced by the speakers to be substantially uniform. Another interesting feature includes that the listener perceives a shift in the position of the source of audible sound by using the audio signal and the compensated audio signal.

Other systems, methods, features and advantages of the invention will be, or will become, apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims.

Drawings

The invention can be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views.

FIG. 1 is an example of a multi-channel compensated audio system;

FIG. 2 is a frequency response of a comb filter, which may be associated with sound emitted from a speaker of the system of FIG. 1;

FIG. 3 is a multi-channel compensated audio system having channel compensation associated with a single channel of the system;

FIG. 4 is the frequency response of the comb filter shown in FIG. 2, and the compensated frequency response generated by using the channel compensation shown in FIG. 3;

FIG. 5 is a multi-channel compensated audio system with channel compensation for multiple channels of the audio system;

FIG. 6 is a single channel of a multi-channel compensated audio system having a multi-channel compensator;

FIG. 7 illustrates channel compensation for all channels in a multi-channel compensated audio system;

FIG. 8 illustrates channel speakers of a multi-channel compensated audio system for use in a passenger compartment of a vehicle;

FIG. 9 is a method for operating a multi-channel compensated audio system with channel compensation;

FIG. 10 is an example multichannel compensated audio system for use in a passenger compartment of a vehicle.

Detailed Description

By selectively frequency equalizing the audio signal, deviations in the target frequency response at one or more listening positions within the listening space (such as at the position of a passenger in the vehicle) may be at least partially accounted for. For example, by providing equalization to the affected channels, comb filtering effects associated with the channels may be at least partially addressed. Such equalization may involve providing a frequency boost and/or a frequency reduction directly to the channel to correct for troughs (dip) and peaks in the target frequency response that represent deviations. Even though the deviation in the target frequency response for a given channel may depend on the listener's position in the listening space or listening environment, a common frequency equalization setting may be provided on that channel based on the common area within the listening space or listening environment where the listener is located.

Applying equalization directly to the affected channels may not provide satisfactory compensation for deviations in the target frequency response at one or more listening positions, as the equalized signals emitted by the channels will still experience reflections. A listener located somewhere within the listening space may receive the equalized signal emitted by the channel and a delayed version of the equalized signal from the reflecting surface. Thus, the equalization may for example only result in a change in the frequency response of the comb filter, which does not adequately compensate for deviations in the sound emitted by the channel.

Some multi-channel audio sound systems, the corresponding listening environment, may have a limited amount of space. One such environment is the passenger compartment of a vehicle. When space in the listening environment is limited, the mass and placement of these speakers within the cabin is likely to be limited as well. For example, due to design constraints on the overall design of the vehicle cabin, speakers for audio channels may need to be positioned at less than optimal locations within the vehicle cabin. Further, speakers with speaker qualities that differ from each other may be used based on cost constraints, available space for speakers, and other criteria. This difference in the quality and placement of the speakers in the listening environment may also be one of the causes of a deviation in the target frequency response at the listening position unless appropriate channel compensation is applied.

FIG. 1 is an exemplary multi-channel compensated audio system that may employ channel compensation. Two channels of the multi-channel compensated audio system are shown in fig. 1, but more channels may be employed. The multi-channel compensated audio system of fig. 1 is shown without enabling channel compensation. As used herein, the term "multi-channel" describes two or more audio channels provided within an input audio signal for driving two or more speakers. Example multi-channel audio signals include stereo audio signals, 5.1 channel audio signals, 6.1 channel audio signals, 7.1 audio signals, or any other audio signal that includes two or more audio channels.

The multi-channel compensated audio system may include one or more processors (such as digital signal processors) and memory. The operation of the multi-channel compensated audio system may be based on instructions, software or code stored in memory that are executed by a processor, electronic hardware, and devices and systems controlled by a processor, or some combination. The memory may include volatile, non-volatile, flash, magnetic, or any other form of non-transitory memory capable of storing executable instructions, information/parameters of the audio system, user-specified configuration information, and data such as audio content, audio-visual content, or any other information capable of being stored and accessed. The multi-channel compensated audio system may also include a user interface capable of receiving user input and providing information to a user of the system. In addition, the multi-channel compensated audio system may include an amplifier, an audio source, and a wired or wireless interface to external devices, as well as functions such as navigation, long distance communication, satellite communication, desktop computing, and any other function or capability.

The multi-channel compensated audio system may include a first audio signal 110 provided uncompensated to a first speaker 115. The second audio signal 120 may be provided to the second speaker 125 without compensation. The first and second audio signals 110 and 120 may represent audio content present on different audio channels (such as stereo, 5.1, 6.1, or 7.1 audio channels) within an input audio signal of the multi-channel audio system. Sound emitted from each speaker 115 and 125 may propagate in a composite manner into the listening environment 127 and may include multiple interactions between reflective surfaces within the listening environment 127, direct sound 140 and reflected sound 145 from the speaker 115, and direct sound 150 and reflected sound 155 from the second speaker 125.

For the sake of brevity, only the very basic interaction of sound emitted from speaker 115 in listening environment 127 is illustrated. In this simplified representation, a listener located at a listening position 135 within a listening environment 127 receives direct sound 140 from the speaker 115 and sound 145 from the speaker 115 reflected by the reflective surface 130. In this manner, a listener at a listening position 135 in the listening environment 127 is presented with both direct sound 140 and a delayed version of sound 145, which may result in constructive and destructive interference, which may produce deviations in the target frequency response, such as comb filtering effects. In other examples, there may be more speakers, more listening positions, and more reflective surfaces.

An exemplary comb filter response representing a deviation in the target frequency response is shown in fig. 2. As shown, the comb filter's frequency response 200 includes a series of regularly spaced peaks 205 and valleys 210 exhibiting a comb-like profile. The user at the listening position 135 receives a sound having a frequency response different from the original sound emitted by the speaker 115. As used herein, a deviation in the target frequency response refers to: the audible sound received by a listener listening to a location within the listening space does not fall within the desired frequency response range. Comb filtering is just one example to describe the deviation of the target frequency response, but as discussed herein, comb filtering should be taken as a representative, non-limiting example and should be interchangeable with other forms of deviations of the target frequency response psychoacoustically perceived by a listener listening to a location within a listening space. As used herein, the term "psychoacoustically perceived" or "perception" or "psychoacoustic perception" refers to the awareness, observation, and discrimination of a listener with respect to the sound field experienced by the listener in a listening area or listening space.

Fig. 3 shows another example of the multi-channel compensated audio system of fig. 1 with single channel compensation. In fig. 3, a first audio signal 110 is provided to a speaker 115 as audio content for a single channel in an input audio signal. As in FIG. 1, a listener at a listening position 135 of a listening space 127 receives direct sound 140 and reflected sound 145 from a speaker 115, the speaker 115 being driven by a first audio signal 110. To compensate for direct and indirect sounds present in the listening environment 127, the audio signal 110 is also provided to the input of the compensation channel 305.

The compensation channel 305 may include a series connection of a delay circuit 310, a level adjuster circuit 313, and an equalizer circuit 315 through which the audio signal 110 is processed. Delay circuit 310, level adjuster circuit 313, and equalizer circuit 315 may be modules, hardware (such as electronic circuits, registers, and circuit devices), or a combination of instructions and hardware, comprised of instructions stored in a memory and executable by a processor. The delay circuit 310 may be used to selectively add a delay to a frequency or different frequency range included in the audio signal 110. As described later, this delay may be used to preserve the physical direction or position of the sound produced in the listening space. The level adjuster circuit 313 may be used to adjust the spectral energy of the audio signal in its entirety to enhance or attenuate the energy level of the audio content throughout the entire frequency range represented in the audio signal 110. As described later, adjustments to the energy level of the audio signal may reduce or increase the overall amplitude of the audible sound output by the speaker. The equalization circuit 315 may be used to selectively enhance and attenuate the energy levels of individual frequencies or different frequency ranges included in the audio signal 110. In some examples, equalization circuit 315 may also perform overall amplitude adjustment on the audio signal, and level adjustment circuit 313 may be omitted.

The output of the compensation channel 305 constitutes a compensated audio signal 320. The compensated audio signal 320 is provided to an input of the summing circuit 323 together with the second audio signal 120, the second audio signal 120 representing the audio content of another single channel comprised in the input audio signal. The summing circuit 323 adds/subtracts the second audio signal 120 and the compensated audio signal 320 from each other to generate an output signal 325, the output signal 325 being provided to the speaker 125. The speaker 125 plays a sound 330 into the listening environment 127, the sound 330 corresponding to the combination of the second audio signal 120 and the compensated version 320 of the first audio signal 110. As used herein, the term "signal" or "signals" are used interchangeably to describe an electrical signal, or audible sound produced by a corresponding speaker mechanically operating based on a corresponding electrical signal.

In the multi-channel audio system of fig. 3, the amount of delay provided by delay circuit 310, the level adjustment provided by level adjuster 313, and the equalization provided by equalizer circuit 315 may be selected to reduce the comb filtering effect shown in fig. 2, while still maintaining the psycho-acoustic perception of listener 135 that the source of audible sound representing audio content in a single channel is first speaker 115, or is near first speaker 115, and/or is from the direction in which first speaker 115 is physically located.

An example of the resulting frequency response of the compensated sound in the listening environment 127 is shown in fig. 4. The response 200 corresponds to the uncompensated response of the system shown in fig. 1. The frequency response of the compensated audio signal 325, as expressed by sound 330 emitted by speaker 125, is shown as 405. The frequency response 405 includes a peak 410 that appears at the valley 210 of the frequency response 200. Thus, the frequency response 405 is constructively added to the frequency response 200. Response 405 also includes a valley 415 that occurs at peak 205 of frequency response 200. The frequency response 405 does not perform cancellation of any portion of the frequency response 200. Accordingly, the frequency response 405 and the frequency response 200 need not be accurately aligned in phase. Further, the frequency range in frequency response 405 and the frequency range in frequency response 200 may overlap to enable the plurality of valleys 210 to be filled by peaks 410. In this manner, equalization of the frequency response 405 may occur at a frequency or within a range of frequencies that are also present in the frequency response 200.

Also illustrated in fig. 4 is a first average energy level 420 of the compensated audio signal 325, which is shown raised by a determined amount by the level shift circuit 313 to reach a second average energy level 425. The compensated audio signal 325 may be increased (or decreased) such that the amplitude of the peak 410 of the frequency response 405 is more closely aligned with respect to the amplitude of the peak 205 of the frequency response 200. As a result, the frequency response 405 may be maintained at or below a level of the amplitude of the frequency response 200 to avoid being psychoacoustically detected (or psychoacoustically perceived) by a listener as emanating from a physical location that is different from the frequency response 200 or causing a shift in the perceived position of the frequency response 200 over the physical location.

When the frequency responses 200 and 405 are combined with one another in the listening environment 127, the comb filtering effect perceived by a listener in association with the sound emitted by the speaker 115 may be substantially attenuated. In one example, the compensation channel 305 delays, energy adjusts, and equalizes the first audio signal such that sounds received by a listener in the listening environment corresponding to the first audio signal have a comb effect that is minimized and psychoacoustically perceived by the listener as being produced by the first speaker 115.

Referring again to fig. 3, the input signal 110 may drive the first speaker 115 to emit an audible sound that, upon reaching the listening position 135, is perceived by the listener as having a deficiency in the target frequency response. The perceived deficiencies may be a result of deficiencies in the performance of the speaker 115 and/or a result of acoustic interference (e.g., comb filtering at the listening position 135) that exists between the direct path of the direct sound 140 and the reflected path of the reflected sound 145. This results in undesirable dips and peaks in the frequency response at the listening position 135. These artifacts, as perceived by the listener, can be minimized by processing the input signal 110 through the compensation channel 305 and the summing circuit 323. The processed output signal 325 may be sent to the second speaker 125 at a different location of the listening space 127. Because the second speaker 125 is at a different location, it is likely to have different interference, so there may be different peaks and troughs in its response at the listener's position 135. Thus, the compensated signal emitted by the second speaker 125 may be used to attempt to fill some of the "gaps" or valleys in the frequency response due to the first speaker 115. Thus, the valley 210 may be filled by the peak 410 of the audio output from the second speaker while the peak 205 remains substantially unchanged (fig. 4).

When attempting to fill in these "gaps" in the response of the first speaker 115 at the listening position, such filling in these "gaps" may be substantially imperceptible to the listener using psychoacoustics. The audible sound produced by the first speaker 115 in response to the first input signal 110 is generally perceived at the listening position as sound from that direction or position. When the compensated version of the first input signal 110 (compensated audio signal 320) is used to produce audible sound as compensated sound from the second speaker 125 to fill in these "gaps," the compensation may be appropriately delayed and the energy levels appropriately adjusted so that the user still perceives substantially all of the audible sound at the listening position as coming from the first speaker 115, or from the direction of the first speaker 115. In this manner, the listener perceives that the sound source (first speaker 115) is not moving in position, whether second speaker 125 is producing, or is not producing, a compensated audio signal to fill in these "gaps".

Compensating the first input signal 110 to achieve a substantially unchanged perceived position may include applying a predetermined delay to the compensated audio signal 320 emitted by the second speaker 125. The delay may be selected such that the compensated audio sounds produced by the second speaker 125 arrive at the listening position 135 after a predetermined period of time has elapsed after the corresponding audio sounds produced by the first speaker 115. Further, predetermined energy level adjustments and/or predetermined equalization may be selectively applied to the first input signal 110 and/or the compensated audio signal 320 to adjust the spectral energy of the synthesized audible sound produced by the first and second speakers 115 and 125. When the combination of audible sounds produced by the first and second speakers 115 and 125 reaches the listening position 135, the human ear adds the delayed sound energy to the energy of the direct sound while perceiving the originating position and originating direction of the sound. As a result of how the human auditory system and brain work, the listener still positions the received audible sound to originate substantially from the first speaker 115. There may be a limit as to how loud and how much delay the audible sound produced by the second speaker 125 can be relative to the audible sound produced by the first speaker 115 to substantially maintain the position and direction of the sound as perceived by the listener. Such limits may be established by spectral analysis of the listening space, experimentation with test subjects, or any other process (or processes) or test equipment capable of determining limits for delay, energy level, and/or equalization, such as those described before and after, for the psychoacoustic position and direction of the sound source.

The term "substantially" refers to a somewhat less stringent correction for the deviation in the target response due to the first speaker at the listening position 135, since it is not necessary to exactly match the phase and amplitude of the signals from the speakers 115 and 125 in order to achieve the listener's desired perceptual effect. In other words, because no spectral energy cancellation is performed, there is no need to exactly match the phases from the speakers 115 and 125, because adding the existing spectral energy produced by the first speaker 115 (see fig. 4) does not require exact matching of the signal phases. Furthermore, it is desirable that "substantially" maintaining the position and direction of sound can increase the area of the listening position in order to avoid that the correction is only accurate at an exact position in the listening space, so that a relatively small movement of the listener may weaken or defeat the correction. This may be particularly true at the relatively high frequencies of the sound being compensated (where the wavelength is short).

By substantially filling these "gaps" in the frequency response caused by the first speaker 115, the listener perceived response of the first speaker 115 may be improved. Filling or minimizing at least some of the valleys in the frequency response caused by the first speaker 115 results in an improvement in the psycho-acoustically perceived amplitude response of the first speaker 115. The process for adding a delay to the compensated audio signal 320 is dependent on how the human ear works to integrate signals from two different sound sources, such as two different loudspeakers. For example, the human ear may integrate delayed audible sounds formed from the compensated audio signal 325 from the second speaker 125 with the original audio sounds formed from the audio signal 110 from the first speaker 115 such that the delayed sounds are not heard as separate events and all of the sounds are heard from the direction of the first speaker 115.

Such a desired combination of audio sounds generated by the first and second speakers 115 and 125 may effectively minimize deviations in the target frequency response as long as the delay is no greater than a predetermined amount, e.g., between 0 milliseconds and about 40 milliseconds to about 80 milliseconds, with respect to the corresponding audio content of the audio signal driving the first speaker 115, and the energy level of the audible sound from the second speaker 125 is a predetermined amount, e.g., in a range between about +10dB and about-20 dB with respect to the energy level of the corresponding audio content included within the audible sound generated by the first speaker 115.

By minimizing deviations in the target response as substantially as possible, rather than completely eliminating such deviations, correction of the deviations within the audio system may be more robust and the effects on the compensation caused by movement of the listener may be minimized. As a result, the correction may substantially minimize the deviation over a relatively large listening position 135 (such as a seat position within a vehicle), regardless of the height, movement, and head orientation of a listener occupying the listening position 135. Such a change in listener position within the listening position 135 does not result in a perceived change in response amplitude, but may result in a change in response phase. However, since the human ear is less sensitive to differences in phase, the changes perceived by the listener (due to movement within the listening position) to minimize deviation from the target response are advantageously reduced.

The amount of delay provided by delay circuit 310 and the equalization provided by equalizer circuit 315 may also be selected to psychoacoustically correct audible sound generated by the system in one or more listening positions when the audio system uses speakers having different frequency response characteristics, when the listening space has different reflective surface characteristics, or any other environmental or hardware related characteristics that affect audible sound received from the speakers at the listening positions in the listening space.

FIG. 5 is an example of a multi-channel compensated audio system where each channel may include compensation. The compensation channel 305 may be applied in a similar manner as described with reference to fig. 3. In fig. 5, a compensation channel is also associated with the second audio signal 120 to compensate for reflected sound 505 emanating from the speaker 125. A second audio signal 120, representing one of the channels in the multi-channel audio signal, may be applied to an input of a second compensation channel 510, the second compensation channel 510 comprising a second delay circuit 515, a level adjuster circuit 517, and a second equalization circuit 520 connected in series. The compensation channel 510 generates a second compensated audio signal 525 from the second audio signal 120. The first audio signal 110 and the second compensated audio signal 525 may be applied to inputs of a summing circuit 530. The summing circuit 530 adds and/or subtracts the first audio signal 110 and the compensated audio signal 525 with respect to each other to generate a second output signal 535 that is provided to drive the first speaker 115. The first speaker 115 emits sound 140 into the listening environment 127, the sound 140 corresponding to the first audio signal 110 and the compensated version 525 of the second audio signal 120 (compensated audio signal 525).

A listener at the listening position 135 can psychoacoustically perceive the position and direction of sound as coming from the corresponding first and second speakers 115 and 125. In practice, however, the direct and reflected sounds 140 and 145 are compensated to fill in gaps in the sound field perceived by the listener at the listening position 135 by using the second speaker 125 and the audio compensation signal 320. Similarly, the direct and reflected sounds 330 and 505 are compensated to fill in gaps in the sound field perceived by the listener at the listening position 135 using the first speaker 115 and the compensated audio signal 525. In other example systems having additional speakers, two or more of these speakers, and corresponding compensated audio signals, may be used to fill in gaps in the sound field perceived by a listener at the listening position 135, as with the compensation for the first or second speakers 115 and 125.

FIG. 6 is an example multi-channel compensated audio system that includes a compensation system that is extended to more channels. In such a multi-channel compensated audio system, a plurality of audio channels may each provide a respective audio signal. A plurality of compensation channels may be provided, each of which is respectively associated with the audio signal of a respective audio channel. Each audio compensation channel includes a series connection of a delay circuit, a level adjuster circuit, and a frequency equalizer circuit that generates a compensated audio signal from the audio signal of the respective audio channel associated with the compensation channel. A plurality of summing circuits may be used to generate audio output signals for supply to corresponding speakers for each channel in a multi-channel audio system. The plurality of summing circuits may have inputs for receiving an audio signal from a respective one of the plurality of audio channels and a plurality of compensated audio signals for the remaining plurality of audio channels.

An example multi-channel compensated audio system, such as a single channel of a 5.1 audio system, is shown in the example of fig. 6. For simplicity, only a single channel speaker 605 is illustrated. For purposes of the following discussion, it is assumed that the speaker 605 is a front Right (RFC) speaker and is associated with the audio signal 610 of the front right channel of the audio system. The audio signals for the remaining channels, except for the audio system RFC, are provided to a multichannel compensator 615, the multichannel compensator 615 being associated with RFCs, respectively.

The multichannel compensator 615 includes a compensation channel for each audio signal other than RFC. In other examples, the multichannel compensator 615 may include compensation channels for less than all of the remaining audio channels. In FIG. 6, compensation channel 620 receives an audio signal 625 corresponding to a Central Front Channel (CFC) of the audio system and generates a corresponding compensated CFC audio signal at 630. The compensation channel 635 receives an audio signal 640 corresponding to the audio system front left channel (LFC) and generates a corresponding compensated LFC audio signal at 640. Compensated channel 650 receives an audio signal 655 corresponding to an audio system rear left channel (LRC) and generates a corresponding compensated LRC audio signal at 660. The compensation channel 665 receives an audio signal 670 corresponding to a Right Rear Channel (RRC) of the audio system and generates a corresponding compensated RRC audio signal at 675. The compensation channel 680 receives an audio signal 685 corresponding to a Low Frequency Effects (LFE) channel of the audio system and generates a corresponding compensated LFE audio signal at 690 that represents a low frequency portion of the audio signal.

The audio signal 610 and each of the compensated audio signals 630, 645, 660, 675, and 690 are provided to a summing circuit 693. The summing circuit 693 adds and/or subtracts the audio signals at its inputs to generate an output signal 695, which is provided to the speaker 605. In this manner, the audio signal 695 provided to the speaker 605 corresponds to the uncompensated version 610 of the audio signal for that audio channel, as well as the compensated audio signal for each of the remaining audio channels. Depending on design criteria, the compensated audio signals for certain channels need not be provided by the multi-channel compensator 615.

The system topology can be extended to each of the remaining audio channels as shown in fig. 7. For example, the speaker 705 of the CFC channel receives an output signal 707 corresponding to the uncompensated CFC audio signal version 625, and the compensated RFC, LFC, RRC, RLC and LFE audio signal versions 713 provided by the multi-channel compensator 715. The LFC speaker 720 receives an output signal 723, which corresponds to the uncompensated LFC audio signal version 640, and the compensated RFC, CFC, RRC, RLC and LFE audio signal version 717 provided by the multi-channel compensator 727. The speaker 730 of the RRC channel receives an output signal 733 corresponding to the uncompensated RRC audio signal version 655 and the compensated RFC, CFC, LFC, RLC and LFE audio signal version 731 provided by the multi-channel compensator 737. The speaker 740 of the RLC receives an output signal 743 corresponding to the uncompensated RLC audio signal version 670 and the compensated RFC, CFC, LFC, LLC and LFE audio signal version 741 provided by the multi-channel compensator 747. The speaker 750 of the LFE channel receives an output signal 753 corresponding to an uncompensated LFE audio signal version 685, and compensated RFC, CFC, LFC, LLC, and RRC audio signal version 751 provided by a multi-channel compensator 757. Although the multi-channel audio systems of fig. 6 and 7 are described in the context of a 5.1 channel system, this topology is extendable to multi-channel audio systems having more audio channels, such as 6.1 or 7.1 systems, or multi-channel audio systems having fewer audio channels, such as stereo systems.

Fig. 8 is an example of a speaker arrangement for a multi-channel compensated audio system, such as a 5.1 system, in a vehicle 805. These speakers in the system of fig. 8 play sound into a listening environment 815 formed by the passenger compartment of the vehicle 805. In this example, a listening position 820 in the form of a driver's seat is located in the listening environment 815.

Each compensation channel of the audio system may have its own unique delay, level adjustment and equalization features. These features may be selected based on psychoacoustic perception of a listener at a listening position 820 within the listening environment 815. For this purpose, the listener at the listening position 820 may be replaced with a dummy head having two ears. The dummy head with the ears may be placed at a fixed location and/or multiple listening positions within the listening environment 815, such as a driver position, a front passenger position, and a rear passenger position. The delay, energy level and equalization characteristics of the compensation channel can be adjusted using sound measurements detected at a dummy head with two ears. The sound measurement at the dummy head with the ears may be compared to a plurality of sound measurements associated with different psychoacoustic characteristics. The delay, energy level and equalization of the compensation channel may be changed until the sound measurements detected at the dummy head with ears correspond to the desired psychoacoustic characteristics at each listening position.

The dummy head with both ears may be moved to multiple listening positions within the listening environment 815 while changing the delay, level adjustment and equalization characteristics of the compensation channel. In this way, the delay, energy level, and equalization values for these compensation channels may be set to values that provide psychoacoustic perceptual characteristics that are acceptable to all listeners at different listening positions within the listening environment 815.

The multi-channel audio system of the vehicle 805 may include a plurality of delay, energy levels, and equalization settings that are optimized for the psychoacoustic perception of audio by a listener at one or more listening positions in the listening environment 815. To this end, a listener at a particular listening position may be provided with selections associated with listeners at one or more listening positions within the listening environment 815 (i.e., driver position, rear car, passenger position, all positions). In fig. 8, the listening position 820 is at the driver position, which corresponds to the selection "driver position" on the audio system user interface. When selected, the delay, energy level, and equalization values of the compensation channel may be used to substantially minimize the deviation in the target response at the listening position 820 for all or some of the speakers 605, 705, 720, 730, 740, 750, while maintaining the perceived position and direction of the sound as coming from the speakers 605, 705, 720, 730, 740, 750.

Alternatively or additionally, the delay, energy level, and equalization values of the compensation channel may be used to substantially minimize the deviation in the target response, and also to generate one or more virtual channel speaker sounds that are psychoacoustically perceived by a listener to be located at a different location than the actual physical location of the corresponding channel speaker. For example, applying the delay and equalization values to the audio channels may result in virtual movement of the speaker 705 for the CFC to the virtual speaker location shown at 830 and/or virtual movement of the speaker 720 to the virtual speaker location shown at 832. The new virtual speaker locations 830 and/or 832 effectively shift the CFCs and/or LFCs so that they are perceived as being located at more favorable locations for the listener at the driver listening location 820. Similar virtual speaker shifts may be provided for any one or any plurality of the remaining speakers. In this manner, substantially all or some of the speakers may be psychoacoustically shifted (in this case, counterclockwise shifted) relative to the actual positions of the channel speakers so that the system is perceived by a listener at the listening position 820 as if the listener were located at a central location within the listening environment 815. Other location optimizations may also be selected through the audio system interface. For example, when the user selects the "all positions" option, the delay, energy level, and equalization values for these compensation channels may be set to provide psycho-acoustic perceptual characteristics that are substantially acceptable to listeners in all listening positions of environment 815.

The loudspeakers of the multi-channel audio system do not necessarily have the same sound reproduction quality or frequency response range with respect to each other. Constraints in system design may force the use of different quality speakers for different channels within the listening environment 815. For example, in the case of a listening space in a vehicle, the size of the speaker 705 for the CFC may be constrained by the limited space available on the dashboard of the vehicle. The remaining speakers may have additional space available to them so that a higher quality speaker or a speaker with a wider desired frequency response range may be used for other channels. In this manner, two or more speakers may have different psycho-acoustically perceived audio frequency responses throughout the audio frequency range in the listening environment 815. The delay, energy level and frequency characteristics of the compensation channel may be used to alter the psychoacoustically perceived audio frequency response of at least one of two or more speakers having different psychoacoustically perceived audio responses.

For purposes of discussion, the CFC speaker 705 may have a substantially irregular frequency response throughout the audio frequency range when compared to one or more of the other channel speakers of the audio system. The delay, energy level, and frequency characteristics of the compensation signals provided by the other channels of the system may be used to correct for such "irregular" frequency responses such that the psychoacoustically perceived frequency response of CFC speaker 705 approaches a target frequency response, such as a substantially flat frequency response over a desired range of frequencies. Additionally, or alternatively, the delay and frequency characteristics of the compensation signals provided by other channels of the system may be used to correct for such "irregular" frequency responses such that the psychoacoustically perceived frequency response of the CFC speaker approaches the psychoacoustically perceived frequency response of other channel speakers of the audio system, regardless of whether the other channel speakers have a desired target frequency range, such as a substantially flat frequency response over the desired frequency range.

Quality correction may also be performed using compensation to minimize undesirable speaker characteristics, such as coloration (coloration), distortion, and any other undesirable speaker characteristics. This correction for channel speakers with different performance in the audio system may also be extended to other speakers than CFC speaker 705.

An example method for operating a multi-channel compensated audio system is illustrated in fig. 9. At 905, the audio system receives a first audio signal and at 910 receives a second audio signal. A first compensated audio signal corresponding to the first audio signal is generated at 915. The first compensated audio signal corresponds to a delayed, level-shifted and equalized version of the first audio signal. A second compensated audio signal corresponding to the second audio signal is generated at 920. The second compensated audio signal corresponds to a delayed, level-shifted and equalized version of the second audio signal. The first audio signal and the second compensated audio signal are added at 925 to generate a first output signal, while the second audio signal and the first compensated audio signal are added at 930 to generate a second output signal. The first output signal is provided to a first speaker at 935. The second output signal is provided to a second speaker at 940. The delay, level shift, and equalization values used to generate the first and second compensated audio signals may be selected to correct for deviations in the desired target response at one or more listening positions without changing the psychoacoustically perceived position and direction of sound generated by the first and second speakers. Additionally or alternatively, the first and second compensated audio signals may be used to generate virtual speaker sounds that are psychoacoustically perceived by a listener in the listening environment to be located at a different location than the actual locations of the first and second speakers in the listening environment. Further, the values of delay, level shift, and equalization may be selected to correct for differences in acoustic quality of speakers used in the audio system.

FIG. 10 is another example multi-channel compensated audio system included in a listening environment in the form of a vehicle. Although illustrated as a passenger compartment of a vehicle having five speakers, in other examples, any other listening area and any number of speakers may be used. With further reference to fig. 1-9, consider signals going to a center speaker 1003 and arriving at a listener position 1002. The frequency response at the listener position 1002 may deviate from the desired target response for at least two different reasons. One possible reason is that the center speaker 1003 has a frequency response that is different in nature from the desired target response. For example, the center speaker 1003 may have a trough and a peak in its response. Another example is when the speaker 1003 is physically small and therefore cannot adequately reproduce low-frequency audio content. This may be the case for center channel speakers in a vehicle. In these circumstances, other speakers, such as the front left speaker 1001 may be used to generate compensation audio based on the compensated audio signal in an attempt to improve the response of the center speaker 1003 as perceived at the first listening position 1002.

As discussed previously, the center channel audio signal is sent to the center speaker 1003. Further, the center channel audio signal may be processed to generate a compensated audio signal that is sent to the front left speaker 1001. The process is designed to make the perceived response of the center channel speaker 1003 sound close to the target response at the listening position 1002. Such correction of the perceived response may be specific to the listening position 1002.

The delay and level of the compensated audio signal may be set such that the sound source is psychoacoustically perceived by a listener at the listening position 1002 to sound still as if it came from the center speaker 1002. Thus, a predetermined delay may be applied to the compensated audio signal at the front left speaker 1001 such that from the perspective of a listener at the listening position 1002, the sound source is still positioned at the center speaker 1003. Further, for the compensated audio signal, the predetermined energy level should be set such that the compensated audible sound generated from the front left speaker 1001 is loud enough to substantially fill the "gap" (such as a valley) in the response from the center speaker 1003. Thus, the delay may be maintained below a threshold level to avoid a situation where the compensation signal cannot be made loud enough without causing the listener at the listening position 1002 to perceive that a distinct sound source has shifted away from the central speaker 1003.

In this example, the front left speaker 1001 is closest to the listening position 1002 and therefore may have the greatest impact on this listening position 1002 due to the gradually decreasing loudness (energy level) of the speaker as the listener's position is further away from the speaker and due to obstacles in the listening area. For example, in a vehicle, such obstacles in the listening area may include the driver and the front seats 1031 and 1032, which may act as an acoustic barrier and attenuate the sound emanating from the left front speaker 1001 reaching the second listening position 1012. For these reasons, the compensation effect caused by the front left speaker 1001 is substantially inaudible at other listening positions in the vehicle, which may have less detrimental effect on other listening positions in the vehicle. In other words, the correction to the listening position 1002 caused by the front left speaker 1001 may be irrelevant to a considerable extent to the correction to other listening positions in the vehicle.

In the case of the second listening position 1012, a different compensation process for the center speaker 1003 may be applied. For example, a listener at the second listening position 1012 may hear the audio content produced by the central speaker 1003, but the audio content may be attenuated when compared to the listening position 1002 because of the greater distance and the front seats 1031 and 1032 acting as obstacles. The attenuation caused by the front seats 1031 and 1032 may be frequency dependent. Accordingly, a compensation signal may be applied to the right rear speaker 1011 to correct the response to the center speaker 1003 at the second listening position 1012. The selection of the delay and energy level of the compensation signal may be guided by actual measurements, surveys, or any other mechanism, as previously discussed. In one example, more delay may be applied to the left rear speaker 1011 than to the left front speaker 1001 due to the first distance from the left front speaker 1003 to the listening position 1012 being further than the second distance from the right rear speaker 1011 to the listening position 1002. Accordingly, the level of audible sound produced by the right rear speaker 1011 may be relatively louder without a listener at the second listening position 1012 perceiving that the position of the center speaker 1003 has changed. Furthermore, since the right rear speaker 1011 is closer to the second listening position 1012 than to other listening positions, this speaker will have the greatest effect on the audible sound perceived by a listener located at the second listening position 1012.

In another example, the compensated audio signal may be used to enable a listener to perceive that the individual speaker channels sound substantially equal in loudness at substantially all listener positions. For this example, consider the LFC signal 1000 at the front left channel of a multi-channel sound source. Such a multi-channel sound source may include compact discs, broadcast audio content, live audio content, DVD, MP3 files, or any other live or pre-recorded audio content provided as an input signal. Furthermore, the multi-channel sound source may comprise any device or mechanism capable of producing multi-channel audio content, such as an up-mixer (upmixer) for converting audio content having fewer audio channels into audio content having additional audio channels, or a down-mixer (downmixer) for converting audio content having many audio channels into audio content having fewer audio channels. The LFC signal 1000 may be directed to the left front speaker 1001 and emitted through the left front speaker 1001. The acoustic energy level of the LFC signal 1000 may be much louder at the first listener position 1002 than it is at the second listener position 1012 due to the difference in distance and the acoustic barrier between the first and second listener positions 1001 and 1012. Conversely, considering the RRC signal 1006 from the sound source provided on the right rear channel, the RRC signal 1006 may be emitted as audible sound by the right rear speaker 1011. The acoustic energy level of the RRC signal 1006 may be far louder at the second listening position 1012 than it is at the first listening position 1002.

Also considered as part of this example is a third listening position 1030 located approximately in the center of the listening area. At this third listening position 1030, the sound from each of the speakers 1001, 1003, 1004, 1011, and 1021 of the present example may be perceived by a listener located at the third listening position 1030 as being substantially equal. While this is a desirable result for optimal multi-channel playback, in the example vehicle provided, not only is there no seating position at this location, but similar sensations are not perceived at other listening positions within the listening area.

With a multi-channel compensated audio system, all output channels from a sound source may be perceived by a listener at a listening position as being substantially equal in loudness. For example, at the first listener position 1002, the sound from the front left speaker 1001 may be made substantially equal in perceived loudness to the sound from the rear right speaker 1011 without a compensation system by simply increasing the sound level of the audible sound produced by the rear right speaker 1011 to compensate for the attenuation experienced by the audible sound produced by the rear right speaker 1011 on its audio path to the first listener position 1002. While simply boosting the audible sound produced by the right rear speaker 1011 may inherently solve the problem of the perceived level inequality at the first listener position 1002, it may also exacerbate the problem of the perceived level inequality at the second listener position 1012. In some cases, at the second position 1012, the signal from the right rear speaker 1011 may have been perceived by the listener as louder than the signal from the left front speaker 1001. By increasing the level of audible sound produced by the right rear speaker 1011 to accommodate the first listening position 1002, the loudness imbalance at the second listening position 1012 may be made even worse.

Using compensated audio signals with adjusted delays and energy levels may address such loudness imbalances at different listening positions. For example, the second listening position 1012 in the case where the signal from the right rear speaker 1011 is louder than the signal from the left front speaker 1001 is considered in fig. 10. In this example, the LFC signal 1000 on the front left channel may be processed by a compensation channel 1010, the compensation channel 1010 including a delay circuit, a level adjustment circuit, and an Equalizer (EQ) circuit. The settings of the compensation channel 1010 may be predetermined as previously discussed. The compensation delay may be set to be at least long enough so that sound from the front left speaker 1011 reaches the second listening position 1012 before the compensated audio signal from the rear right speaker 1011. More generally, the delays and energy levels may be set such that the sound source continues to be psychoacoustically perceived by a listener at the second listening position 1012 as coming from the speaker 1001. These delay and energy level parameters may be set at the compensation channel 1010 such that a listener at the second listener position 1012 psychoacoustically perceives the sound of the LFC signal 1000 from a sound source to be substantially equal in magnitude to the sound of the RRC signal 1006 from that sound source in the magnitude of the spectral energy. At the same time, these delay and energy level parameters may be set at the compensation channel 1040 such that a listener at the first listening position 1002 perceives the sound of the RRC signal 1006 from the sound source to be equal in loudness to the sound of the LFC signal 1000 from the sound source.

An EQ may be placed on the compensation channel 1010 to compensate for the response of the speaker 1001 at the second listening position 1012. The EQ of the compensation channel 1010 may also be used to attenuate higher frequencies relative to the energy levels of lower frequencies. This may take into account the fact that the human ear cannot integrate higher frequencies as easily as lower frequencies. Thus, for a given delay, the higher frequencies may be attenuated by a predetermined amount to prevent the compensation signal from being heard as a separate sound source and/or to prevent the LFC signal 1000 from shifting its perceived position away from its front left position.

In some cases it may not be possible to make the compensated audio signal at the right rear speaker 1011 loud enough so that the LFC signal 1000 and the RRC signal 1006 of the sound source sound equal in loudness at the second listener position 1012. Before the listener starts experiencing a perceived shift in the sound image, or before the audible compensated audio signal from the right rear speaker 1011 and the signal from the front left speaker 1001 are no longer integrated by the listener's ear at the second listening position 1012, there may be a limit as to how loud the compensated signal at the right rear speaker 1011 can become. When the compensated signal from the right rear speaker 1011 is no longer integrated with the signal from 1001, then the signal from the right rear speaker 1011 will begin to be heard as a separate sound source. To address this issue, additional compensation channels may be employed in an attempt to increase the perceived loudness of the LFC signal 1000 at the second listening position 1012. In fig. 10, a second compensation channel 1020 processes the LFC audio signal 1000 and generates a second compensation signal, which is emitted from a left rear speaker 1021. This second compensation signal may be used to supplement the first compensated audio signal from the right rear speaker 1011. The delay, energy level, and EQ may be predetermined as previously discussed. The loudspeaker closest to the listener position may be used as a first compensation channel for that listener position, with subsequent compensation channels configured according to requirements and desired impact on the sound perceived at the listening position.

In another example, it may be desirable to shift the perceived position of a single speaker channel using a multi-channel compensated audio system. In the example of a multi-channel compensated audio system in a vehicle, the center speaker 1003 is considered to be physically located in the front and center of the listening space (e.g., in the center of the dashboard of the vehicle). When a center channel signal from a sound source is transmitted to the center speaker 1003, a listener at a first listening position 1002 may perceive that the sound is coming from the physical location of the center speaker 1003. In some cases this is acceptable and desirable. However, some listeners may prefer that the sound of the center channel be acoustically perceived as if coming from directly in front of them, even when the center speaker 1003 does not occupy that physical location. Furthermore, at the same time, the perceived center channel sound source should also be perceived by other listeners at other listening positions in the listening space as being located directly in front of all those other listeners.

This may be accomplished using a multi-channel compensated audio system by transmitting a Center Frequency (CFC) signal 1045 from the sound source to the center speaker 1003. Meanwhile, the CFC signal 1045 may be processed through the fourth compensation channel 1050 and the compensated audio signal may be provided to the left front speaker 1001. The predetermined values for the delay, EQ, and energy levels of the fourth compensation channel 1050 may be selected as previously discussed. In this case, the compensation signal emitted by the front left speaker 1001 may be made to reach the first listening position 1002 before the signal from the center speaker 1003 reaches the first listening position 1002. To achieve this, delay circuit 1055 may be used to delay CFC signal 1045 into center speaker 1003.

The compensation delay applied by the delay circuit 1055 for the center speaker 1001 may be positive or negative with respect to the time at which the signal from the front left speaker 1003 reaches the first listening position 1002. The predetermined level of the compensated audio signal emitted by the front left speaker 1001 may be selected based on the selected delay and the relative physical positions of the front left speaker 1001 and the center speaker 1003 with respect to the first listener position 1002. To move the perceived sound source to a point directly in front of the listener in the listening position provided by seat 1032, a substantially similar compensated audio signal may be provided to front right speaker 1004. Similar processing may be used for the left rear speaker 1021 and the right rear speaker 1011 to provide a perceived center channel audio source for the second listening position and other listening positions, such as the rear seats of a vehicle. Furthermore, multiple loudspeakers may be used to shift the position of a given audio source channel signal to a desired perceptual position.

Using a compensation system, different listeners at different listening positions may have different perceived positions for the same sound source channel at the same time. For example, in a vehicle, a driver may want the center channel audio signal from a sound source to be perceived as sounding right in front of the driver's seat, while a passenger in a front seat may want the center channel audio signal to be perceived as sounding from the center of the dashboard, where the center speaker 1003 is actually located.

Similar processing may be used for all source channel signals in order to make them sound from the desired location. In addition to moving the perceived speaker position from side to side, the compensation system may also provide back and forth movement of the perceived speaker position in the listening area. Moreover, if the audio system includes one or more speakers that are physically located at elevated positions relative to other speakers in the audio system, the perceived speaker positions can be moved up and down longitudinally within the listening space. For example, where the entity of one or more speakers is positioned above one or more listening positions (e.g., mounted on a headliner), the perceived speaker position may be moved up and down longitudinally within the listening space of the vehicle. Accordingly, the position of the perceived sound source channel signal may be selectively raised. Similarly, the location of the perceived sound source channel signal may be selectively reduced.

While various embodiments of the invention have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of the invention. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.

Claims (27)

1. An audio system, comprising:

a first compensation channel configured to receive a first audio signal, the first compensation channel comprising a delay circuit and a frequency equalizer circuit connected in series, generating a first compensated audio signal;

a second compensation channel configured to receive a second audio signal, the second compensation channel comprising a delay circuit and a frequency equalizer circuit connected in series, generating a second compensated audio signal;

a first summing circuit having inputs for receiving the first audio signal and the second compensated audio signal, wherein the first summing circuit generates an output signal for providing to a first speaker to generate a first audible sound; and

a second summing circuit having inputs for receiving the second audio signal and the first compensated audio signal, wherein the second summing circuit generates an output signal for providing to a second speaker to generate a second audible sound,

wherein the first compensated audio signal is configured to drive the second speaker, the first compensated audio signal is constructively added to the first audible sound generated by the first speaker at a listening position, and the second compensated audio signal is configured to drive the first speaker to constructively add the second compensated audio signal to the second audible sound generated by the second speaker at the listening position, wherein the constructive addition at the listening position compensates for a deviation in a target frequency response at the listening position.

2. The audio system of claim 1, wherein an output of the first summing circuit is electrically connected to the first speaker and an output of the second summing circuit is electrically connected to the second speaker.

3. The audio system of any of claims 1 or 2, wherein the first and second speakers are located in a listening environment, and wherein a combination of sounds output from the first and second speakers generates a virtual speaker sound that is psychoacoustically perceived by a listener in the listening environment as being located at a different location than the actual locations of the first and second speakers.

4. The audio system of claim 2, where the first and second speakers are located in a listening environment, and where the first and second speakers have different audio frequency responses in a range of audio frequencies in the listening environment.

5. The audio system of claim 4, where the first compensation channel produced by the second speaker as audible sound has delay and frequency equalization features that change a psychoacoustically perceived audio frequency response of sound from the first speaker in the listening environment without changing a listener perceived physical location of the first speaker.

6. The audio system of claim 5, where the frequency equalization characteristic of the second audible sound produced by the second speaker is within the frequency range of the first audible sound produced by the first speaker.

7. The audio system of claim 5, where the second compensation channel produced by the first speaker as audible sound has delay and frequency equalization features that change a psychoacoustically perceived audio frequency response of the second audible sound from the second speaker in the listening environment without changing a listener perceived physical location of the second speaker.

8. The audio system of claim 7, wherein the frequency equalization characteristic of the first audible sound produced by the first speaker is within a frequency range of the second audible sound produced by the second speaker.

9. The audio system of claim 5, wherein the second speaker has a substantially flat frequency response characteristic in the audio frequency range and the first speaker has a substantially irregular frequency response in the audio frequency range, and wherein the first compensation channel produced by the second speaker as audible sound is configured to reduce irregularities in the frequency response of the sound from the first speaker when psychoacoustically perceived in the listening environment.

10. The audio system of claim 1, wherein the first compensation channel and the second compensation channel each further comprise a level adjuster circuit configured to selectively provide adjustment of an overall magnitude of spectral energy of the first compensated output signal and the second compensated output signal.

11. The audio system of claim 2, wherein the first and second speakers are located in a passenger compartment of a vehicle.

12. A multi-channel audio system comprising:

a plurality of audio channels providing respective audio signals;

a plurality of compensation channels, each associated with an audio signal of a respective audio channel of the plurality of audio channels, respectively, wherein each of the audio compensation channels comprises a delay circuit and a frequency equalizer circuit connected in series for generating a compensated audio signal from the audio signal of the respective audio channel; and

a plurality of summing circuits configured to generate audio output signals for provision to corresponding speakers of at least some of the audio channels;

one of the plurality of summing circuits has a first audio output signal to drive a first speaker producing a first frequency response and has an input configured to receive an audio signal from a first respective one of the plurality of audio channels and at least one compensated audio signal generated from an audio signal of at least one second respective one of the plurality of audio channels, and

the at least one second respective audio channel of the plurality of audio channels is configured to drive a second speaker to produce a second frequency response, wherein the at least one compensated audio signal included in the first frequency response is configured to constructively combine with the second frequency response at a listening position to minimize a deviation in a target frequency response at the listening position without changing a position of the second speaker as perceived by a listener.

13. The multi-channel audio system of claim 12 wherein the output of each summing circuit is electrically connected to its corresponding speaker.

14. The multi-channel audio system of any one of claims 12 to 13, wherein the speakers of each channel of the multi-channel audio system are located in a listening environment, and wherein the combination of sounds output from the speakers generates a virtual speaker that is psychoacoustically perceived by a listener in the listening environment as being located at a position that is different from the actual position of one or more of the speakers.

15. The multi-channel audio system of claim 13 wherein the speakers of each channel of the multi-channel audio system are located in a listening environment, and wherein two or more of the speakers have different psychoacoustically perceived audio frequency responses in an audio frequency range of the listening environment.

16. The multi-channel audio system of claim 15 wherein the compensation channel has delay and frequency characteristics that change a psychoacoustically perceived audio frequency response of at least one of the two or more speakers, the two or more speakers having different psychoacoustically perceived audio frequency responses.

17. The multi-channel audio system of claim 16 wherein at least one of the two or more speakers has a substantially irregular frequency response in the audio frequency range when compared to one or more other speakers in the multi-channel audio system.

18. The multi-channel audio system of claim 12, wherein each of the plurality of compensation channels includes a level adjuster circuit configured to adjust an overall energy level of the compensated audio signal.

19. The multi-channel audio system of claim 13 wherein the speakers of each channel of the multi-channel audio system are located in a listening environment, and wherein the sound output from the speakers combine to generate a sound field at different listening positions in the listening environment that is psychoacoustically perceived by a listener in the listening environment as being acted upon substantially equally by at least a plurality of the speakers.

20. A method for operating a multi-channel audio system, comprising:

receiving a first audio signal;

generating a first compensated audio signal by performing a series of delays and frequency equalizations on the first audio signal;

receiving a second audio signal;

generating a second compensated audio signal by performing a series of delays and frequency equalizations on the second audio signal;

generating a first output signal for providing to a first speaker by adding the first audio signal and the second compensated audio signal;

generating a second output signal for providing to a second speaker by adding the second audio signal and the first compensated audio signal;

generating, by the first speaker, a first speaker output based on the first output signal, the first speaker output comprising a frequency response of the first audio signal and a frequency response of the second compensated audio signal;

generating, by the second speaker, a second speaker output based on the second output signal, the second speaker output comprising a frequency response of the second audio signal and a frequency response of the first compensated audio signal; and

minimizing a deviation in a target frequency response at a listening position without changing a psychoacoustically perceived physical location of the first and second speakers by constructively combining a frequency response of the first audio signal with a frequency response of the first compensated audio signal at the listening position, and constructively combining a frequency response of the second audio signal with a frequency response of the second compensated audio signal at the listening position.

21. The method of claim 20, further comprising providing the first and second output signals to the first and second speakers, respectively.

22. The method of any of claims 20 or 21, wherein the second speaker has a substantially flat frequency response in an audio frequency range, and wherein the first speaker has a substantially irregular frequency response in the audio frequency range, the method further comprising:

arranging the first and second speakers in a listening environment;

delaying and equalizing the first audio signal provided to the second speaker to improve a psychoacoustically perceived audio frequency response to the first speaker in the listening environment without changing a psychoacoustically perceived physical position of the first speaker in the listening environment.

23. The method of claim 21, further comprising:

arranging the first and second speakers in a listening environment;

adjusting a delay and frequency equalization of the first audio signal provided to the second speaker and the delay and frequency equalization of the second audio signal provided to the first speaker to generate a virtual speaker sound that is psychoacoustically perceived by a listener in the listening environment to be located in the listening environment at a location that is different from the actual locations of the first and second speakers.

24. The method of claim 20, wherein the first and second speakers are located in a passenger compartment of a vehicle.

25. The method of claim 20, wherein generating the first compensated audio signal and the second compensated audio signal further comprises executing respective level adjusters to adjust an overall energy level of the first and second compensated audio signals.

26. The method of claim 25, wherein the first and second compensated audio signals are generated using series delay, frequency equalization, and energy adjustment to generate audible sound from the first and second speakers that is psychoacoustically perceived by a listener as being substantially equal in amplitude.

27. A multi-channel audio system comprising:

means for receiving a first audio signal;

means for generating a first compensated audio signal by performing a series delay and frequency equalization on the first audio signal;

means for receiving a second audio signal;

means for generating a second compensated audio signal by performing a series delay and frequency equalization on the second audio signal;

means for generating a first output signal for provision to a first speaker by adding the first audio signal and the second compensated audio signal;

means for generating a second output signal for provision to a second speaker by adding the second audio signal and the first compensated audio signal;

means for driving the first speaker based on the first output signal to generate a first speaker output, the first speaker output comprising a first audio signal output portion and a second compensated audio signal output portion;

means for driving the second speaker based on the second output signal to generate a second speaker output, the second speaker output comprising a second audio signal output portion and a first compensated audio signal output portion; and

means for constructively combining the first audio signal output portion output by the first speaker with the first compensated audio signal output portion output by the second speaker at a listening position, minimizing degradation of sound perceived at the listening position, without changing a psychoacoustically perceived physical position of the first speaker.