Acoustic correction apparatus

• US 5,850,453 A
• Filed: 07/28/1995
• Issued: 12/15/1998
• Est. Priority Date: 07/28/1995
• Status: Expired due to Term

• Current Assignee: DTS, Inc. (Adeia, Inc.)
• Original Assignee: SRS Labs Incorporated (Adeia, Inc.)
• Inventors: Kraemer, Alan D., Klayman, Arnold I.
• Primary Examiner(s): Kuntz, Curtis A.
• Assistant Examiner(s): Mei, Xu
• Application Number:
  US08/508,593
• Time in Patent Office: 1,236 Days
• Field of Search: 381/1, 381/17, 381/18, 381/98, 381/103, 381/86
• US Class Current: 381/1
• CPC Class Codes: H03G 5/025 Equalizers; Volume or gain control in limited frequency bands
• CPC Class Codes: H04R 2499/13 Acoustic transducers and sound field adaptation in vehicles
• CPC Class Codes: H04R 5/02 Spatial or constructional arrangements of loudspeakers
• CPC Class Codes: H04S 1/002 Non-adaptive circuits, e.g. manually adjustable or static, for enhancing the sound image or the spatial distribution control circuits for electronic adaptation of the sound field H04S7/30
• CPC Class Codes: H04S 3/00 Systems employing more than two channels, e.g. quadraphonic H04S5/00, H04S7/00 take precedence

Abstract

An acoustic correction apparatus processes a pair of left and right input signals to compensate for spatial distortion as a function of frequency when said input signals are reproduced through speakers in a sound system. The sound-energy of the left and right input signals is separated and corrected in a first low-frequency range and a second high-frequency range. The resultant signals are recombined to create image-corrected audio signals having a desired sound-pressure response when reproduced by the speakers in the sound system. The desired sound-pressure response creates an apparent sound image location with respect to a listener. The image-corrected signals may then be spatially-enhanced to broaden the apparent sound image.

Claims

1. An audio correction device adaptable to an automotive sound system of a vehicle for spatially enhancing a stereo image projected by the automotive sound system with respect to a listener situated within a driver seat of the vehicle, said vehicle also having a forward-section passenger seat and said automotive sound system comprising a pair of speakers mounted within a respective driver-side door and passenger-side door of the vehicle wherein the speakers are positioned beneath a pair of ears of the listener, said audio correction device comprising:

a stereo image correction circuit connected to said automotive sound system for receiving a stereo sound signal, said stereo sound signal exhibiting audio distortion with respect to said listener when played through said speakers, said image correction circuit modifying components of said stereo sound signal to generate a corrected stereo sound signal, said corrected stereo sound signal compensating for said audio distortion to provide an apparent sound image for said listener when said corrected stereo sound signal is played through said speakers; and

a stereo image enhancement circuit receiving said corrected stereo sound signal for broadening said apparent sound image, said stereo image enhancement circuit modifying said stereo sound signal to generate a spatially enhanced sound signal for playback through said speakers, said image enhancement circuit comprising;

means for generating a difference signal representing the stereo informational content of said stereo sound signal;

an equalizer for applying a level of amplitude boost to said difference signal as a function of frequency wherein said level of boost is characterized by a maximum gain below 200 hertz and characterized by a minimum gain between 1 kHz and 5 kHz; and

means for combining said difference signal with said stereo signal to create said spatially enhanced sound signal.

2. The audio correction device of claim 1 wherein said stereo image correction circuit divides an audible frequency spectrum into a low frequency range and a high frequency range relative to said low frequency range, said image correction circuit modifying components of said stereo sound signal within said low frequency range independently of components within said high frequency range.

3. The audio correction device of claim 1 wherein said distortion results from placement of said speakers within said door whereby said speakers are pointed towards respective sides of said listener, said speakers characterized by an angle of sound dispersion such that said listener'"'"'s ears are positioned substantially outside of said angle of sound dispersion.

4. The audio correction device of claim 3 wherein playback of said spatially enhanced sound signal through said speakers has an apparent effect of rotating said apparent sound image towards said listener, and wherein said minimum gain of said difference signal is a function of said position of said speaker system with respect to said listener.

5. The audio enhancement device of claim 1 wherein said distortion results from sound-absorption characteristics of an interior of said vehicle.

6. An audio enhancement apparatus operative upon left and right stereo input signals provided by a stereo reproduction device for playback through a speaker system having a fixed location within an audio reproduction environment, the enhancement apparatus modifying the stereo input signals to obtain an improved stereo image by compensating for acoustic limitations created when the input signals are reproduced by the speaker system within the audio reproduction environment, the audio enhancement apparatus comprising:

a stereo image correction circuit receiving the left and right stereo input signals and modifying said input signals to generate energy-corrected left and right stereo signals, said energy-corrected left and right signals creating a corrected spatial response when played through said speaker system and heard by a listener in said audio reproduction environment, said corrected spatial response creating an apparent sound image with respect to said listener to obtain a realistic and redirected sound experience for said listener;

a stereo image enhancement circuit receiving the energy-corrected left and right stereo signals and generating enhanced left and right stereo signals for enhancing said apparent sound image to provide an improved sound image perceived by said listener when said enhanced left and right stereo signals are reproduced through said speaker system;

wherein said energy-corrected left and right signals are characterized by a first difference-signal component representing the difference between said energy-corrected left and right signals, and said enhanced left and right stereo signals are characterized by a second difference-signal component representing the difference between said enhanced left and right signals, said second difference-signal component selectively equalized with respect to said first difference-signal component; and

wherein said stereo image enhancement circuit comprises an equalizer for altering a frequency response of said first difference signal to create said second difference signal by applying a perspective equalization curve to said first difference signal, said perspective equalization curve characterized by a maximum-gain turning point occurring at a maximum-gain frequency within a first frequency range of approximately 100 to 200 hertz and said curve characterized by a minimum-gain turning point occurring at a minimum-gain frequency within a second frequency range of approximately 1680 to 5000 hertz.

7. The audio enhancement apparatus of claim 6 wherein said maximum gain is within a range of approximately 10 to 15 dB, and said minimum gain is within a range of approximately 0 to 10 dB.

8. The audio enhancement apparatus of claim 6 wherein said maximum gain, said maximum-gain frequency, said minimum gain, and said minimum-gain frequency are dependent upon said fixed location of said speaker system with respect to said listener.

9. The audio enhancement apparatus of claim 6 wherein said perspective equalization curve is a function of an angle created between (1) the path of direct-field sound emanating from said speaker system and impinging upon a proximate ear of said listener, and (2) a plane parallel to said listener'"'"'s forward line-of-sight.

10. A stereo enhancement device for inputting a pair of stereophonic left and right audio signals and providing processed left and right audio signals to a speaker system for reproduction of a sound image corresponding to said processed signals, said stereo enhancement device comprising:

means for selectively altering the amplitude levels of the left and right audio signals to create corrected left and right audio signals, said corrected left and right audio signals conveying a perceived source of origin for said sound image with respect to a listener when said corrected signals are played through the speaker system, said perceived source of origin distinct from an actual source of origin for said sound image; and

means for enhancing said corrected left and right audio signals to emphasize reverberant sound energy present in said corrected left and right audio signals, said means for enhancing producing said processed left and right audio signals, wherein said means for enhancing comprises;

means for accessing a difference signal representing the difference between said corrected left audio signal and said corrected right audio signal;

means for boosting components of said difference signal within a first and second range of frequencies relative to components of said difference signal within a third range of frequencies to create a processed difference signal, said third range of frequencies greater than said first range of frequencies and less than said second range of frequencies; and

means for combining said sum signal and said processed difference signal with said corrected left and right audio signals to create said processed left and right audio signals.

11. The stereo enhancement apparatus of claim 10 wherein said difference signal has a minimum-gain turning point occurring at a minimum-gain frequency within said third range of frequencies, said minimum-gain turning point determined as a function of said actual source of origin for said sound image.

12. The stereo enhancement apparatus of claim 10 wherein said components of said difference signal within said first, second, and third range of frequencies are all amplified by said means for boosting.

13. A spatial enhancement apparatus for redirecting and enhancing a stereophonic image emanating from a speaker system located within an audio reproduction environment, said spatial enhancement apparatus comprising:

an acoustic-image correcting circuit receiving an audio input signal and producing a corrected audio signal, said audio input signal creating a first sound-pressure response with respect to a listener when played through the speaker system, and said corrected audio signal creating a second sound-pressure response when played through said speaker system, said second sound-pressure response generating an apparent stereo image corresponding to an apparent location of said speaker system with respect to said listener; and

an acoustic-image enhancement circuit receiving said corrected audio signal and providing an enhanced audio signal for reproduction through said speaker system, said enhanced audio signal equalized with respect to said corrected audio signal to broaden said apparent stereo image, wherein the corrected audio signal is a stereophonic signal comprising a difference signal representing the amount of stereo information present in the corrected audio signal, the acoustic-image enhancement circuit equalizing said difference signal according to a perspective level of equalization to create a processed difference signal, the perspective level of equalization varying with respect to frequency of said difference signal and characterized by;

a maximum gain occurring at a maximum-gain frequency within a first frequency range of approximately 100 to 200 hertz and a minimum gain occurring at a minimum-gain frequency within a second frequency range of approximately 1680 to 5000 Hz, said level of equalization decreasing below said first frequency range and above said first frequency range towards said minimum-gain frequency, said level of equalization further increasing above said minimum-gain frequency.

14. The acoustic correction apparatus of claim 13 wherein said maximum gain and said minimum gain are a function of an actual location of said speaker system relative to a listener within said audio reproduction environment.

15. The acoustic correction apparatus of claim 13 wherein said level of equalization of said difference signal is further characterized by bass attenuation of said difference signal relative to said maximum gain, said bass attenuation occurring below said maximum-gain frequency and said bass attenuation increasing with a reduction in difference-signal frequency.

16. The acoustic correction apparatus of claim 13 wherein said maximum gain and said minimum gain are fixed at preset gain levels, said maximum gain and said minimum gain dependent upon the angle of incidence of direct-field sound emanating from an actual location of said speaker system and reaching an ear of said listener.

17. A spatial enhancement apparatus for redirecting and enhancing a stereophonic image emanating from a speaker system located within an audio reproduction environment, said spatial enhancement apparatus comprising:

an acoustic-image correcting circuit receiving an audio input signal and producing a corrected audio signal, said audio input signal creating a first sound-pressure response with respect to a listener when played through the speaker system, and said corrected audio signal creating a second sound-pressure response when played through said speaker system, said second sound-pressure response generating an apparent stereo image corresponding to an apparent location of said speaker system with respect to said listener, wherein said audio input signal comprises a left input signal and a right input signal, and said acoustic-image correcting circuit comprising;

a first energy-correction device receiving said left input signal for processing said left input signal to generate a corrected left audio signal, said first energy-correction device comprising;

a low-frequency correction circuit receiving said left input signal and providing a corrected low-frequency left signal, said low-frequency correction circuit boosting amplitude components of said left input signal within a first frequency range;

a high-frequency correction circuit receiving said left input signal and providing a corrected high-frequency left signal, said high-frequency correction circuit adjusting amplitude components of said left input signal within a second frequency range;

means for combining said corrected low and high-frequency left signals to create said corrected left audio signal;

a second energy-correction device receiving said right input signal to generate a corrected right audio signal, said second energy-correction device comprising;

a low-frequency correction circuit receiving said right input signal and providing a corrected low-frequency right signal, said low-frequency correction circuit boosting amplitude components of said right input signal within said first frequency range;

a high-frequency correction circuit receiving said right input signal and providing a corrected high-frequency right signal, said high-frequency correction circuit adjusting amplitude components of said right input signal within said second frequency range; and

means for combining said corrected low and high-frequency right signals to create said corrected right audio signal; and

an acoustic-image enhancement circuit receiving said corrected audio signals and providing enhanced audio signals for reproduction through said speaker system, said enhanced audio signals equalized with respect to said corrected audio signals to broaden said apparent stereo image.

18. A spatial enhancement apparatus for redirecting and enhancing a stereophonic image emanating from a speaker system located within an audio reproduction environment, said spatial enhancement apparatus comprising:

an acoustic-image correcting circuit receiving an audio input signal and producing a corrected audio signal, said audio input signal creating a first sound-pressure response with respect to a listener when played through the speaker system, and said corrected audio signal creating a second sound-pressure response when played through said speaker system, said second sound-pressure response generating an apparent stereo image corresponding to an apparent location of said speaker system with respect to said listener; and

an acoustic-image enhancement circuit receiving said corrected audio signal and providing an enhanced audio signal for reproduction through said speaker system, said enhanced audio signal equalized with respect to said corrected audio signal to broaden said apparent stereo image wherein the acoustic-image enhancement circuit comprises;

a first summing network inputting corrected left and right audio signals supplied by the acoustic-image correcting circuit, said first summing network generating a difference signal and a sum signal, said difference signal representing the amount of stereo information present in said corrected left and right audio signals;

an equalizer connected to said first summing network, said equalizer modifying the frequency response of said difference signal to create a processed difference signal having a level of equalization varying with respect to frequency of said processed difference signal, said level of equalization characterized by;

a maximum gain occurring at a maximum-gain frequency between approximately 100 to 200 Hz and a minimum gain occurring at a minimum-gain frequency between approximately 1680 to 5000 Hz;

mid-range attenuation of said difference signal relative to said maximum gain, said mid-range attenuation occurring above said maximum-gain frequency and increasing with a corresponding increase in difference-signal frequency up to said minimum-gain frequency, said mid-range attenuation decreasing above said minimum-gain frequency with an increase in difference-signal frequency; and

a signal mixer receiving the processed difference signal and combining the processed difference signal with the sum signal and the corrected left audio signal to create an enhanced left output signal for reproduction by said speaker system, the signal mixer also combining the processed difference signal with the sum signal and the corrected right audio signal to create an enhanced right output signal for reproduction by said speaker system.

19. An audio enhancement apparatus operative upon left and right stereo input signals provided by a stereo reproduction device for playback through a speaker system having a fixed location within an audio reproduction environment, the enhancement apparatus modifying the stereo input signals to obtain an improved stereo image by compensating for acoustic limitations created when the input signals are reproduced by the speaker system within the audio reproduction environment, the audio enhancement apparatus comprising:

a stereo image correction circuit receiving the left and right stereo input signals and modifying said input signals using at least a first frequency correction circuit within a first frequency range and a second frequency correction circuit within a second frequency range on each of said input signals to generate corresponding energy-corrected left and right stereo signals, said energy-corrected left and right signals creating a corrected spatial response in at least a vertical direction when played through said speaker system and heard by a listener in said audio reproduction environment, said corrected spatial response creating an apparent sound image with respect to said listener to obtain a realistic and redirected sound experience for said listener;

a stereo image enhancement circuit receiving the energy-corrected left and right stereo signals and generating enhanced left and right stereo signals for enhancing said apparent sound image to provide an improved sound image perceived by said listener when said enhanced left and right stereo signals are reproduced through said speaker system; and

wherein said energy-corrected left and right signals are characterized by a first ambient component, and said enhanced left and right stereo signals are characterized by a second ambient component ambient component selectively equalized with respect to said first ambient component and wherein said stereo image enhancement circuit comprises an equalizer for altering a frequency response of said first ambient component to create said second ambient component by applying a perspective equalization curve to said first ambient component, said perspective equalization curve characterized by a maximum-gain turning point occurring at a maximum-gain frequency within a first frequency range, said perspective equalization curve further characterized by a minimum-gain turning point occurring at a minimum-gain frequency within a second frequency range, said minimum-gain frequency greater than said maximum-gain frequency.

20. A stereo enhancement device for inputting a pair of stereophonic left and right audio signals and providing processed left and right audio signals to a speaker system for reproduction of a sound image corresponding to said processed signals, said stereo enhancement device comrising:

a first means for selectively altering the amplitude levels of the left and right audio signals at a first frequency range and a second means for selectively altering the amplitude levels of the left and right audio signals at a second frequency range to create corresponding corrected left and right audio signals, said corrected left and right audio signals conveying a perceived source of origin for said sound image with respect to a listener when said corrected signals are played through the speaker system, said perceived source of origin vertically distinct from an actual source of origin for said sound image; and

means for enhancing said corrected left and right audio signals to emphasize reverberant sound energy present in said corrected left and right audio signals, said means for enhancing producing said processed left and right audio signals, wherein said means for enhancing comprises;

means for generating a sum of said corrected left audio signal and said corrected right audio signal;

means for processing the difference information between said corrected left audio signal and said corrected right audio signal;

means for boosting components of said difference information within a first and second range of frequencies relative to components of said difference information within a third range of frequencies to create processed difference information, said third range of frequencies greater than said first range of frequencies and less than said second range of frequencies; and

means for combining said sum and said processed difference information to create said processed left and right audio signals.

21. The stereo enhancement apparatus of claim 20 wherein said difference information has a minimum-gain turning point occurring at a minimum-gain frequency within said third range of frequencies, said minimum-gain turning point determined as a function of said actual source of origin for said sound image.

22. The stereo enhancement apparatus of claim 20 wherein said components of said difference information within said first, second, and third range of frequencies are all amplified by said means for boosting.