Method and system for enhancing audio signals

• US 6,606,388 B1
• Filed: 02/17/2000
• Issued: 08/12/2003
• Est. Priority Date: 02/17/2000
• Status: Expired due to Fees

• Current Assignee: Arboretum Systems Incorporated
• Original Assignee: Arboretum Systems Incorporated
• Inventors: Lindahl, Aram, Townsend, Chris
• Primary Examiner(s): Harvey, Minsun Oh
• Assistant Examiner(s): Grier, Laura A.
• Application Number:
  US09/506,417
• Time in Patent Office: 1,272 Days
• Field of Search: 381/1, 381/61, 381/63, 381/98, 381/99, 381/17, 381/18, 846/25, 846/60
• US Class Current: 381/17
• CPC Class Codes: G10H 1/125 using a digital filter
• CPC Class Codes: G10H 2210/295 Spatial effects, musical uses of multiple audio channels, e.g. stereo
• CPC Class Codes: H03G 5/005 of digital signals
• CPC Class Codes: H04S 1/007 in which the audio signals are in digital form data reduction aspects thereof based on psychoacoustics G10L19/02

Abstract

A technique for enhancing audio signals generated from compressed digital audio files is described. The technique uses a Bass Maximizer module, a Harmonic Exciter module and a Quasi Stereo module. The Bass Exciter module enhances the intensity, depth and punch of the bass audio content by creating harmonic sequences from low frequency components contained in the original input signal. The Harmonic Exciter module adds to the treble audio content of the original input signal by generating harmonic series from the high frequency components contained in the input signal. The Quasi Stereo Module creates a stereo image of the enhanced input signal by adding and subtracting delayed and filtered versions of the enhanced input signal with itself to create left and right channeled stereo-like outputs. The technique provides a useful tool to regenerate from an audio signal more pleasant and joyful sounds.

Claims

1. A method for enhancing the quality of an audio signal, the method comprising:

separating said audio signal into a first signal having low frequency components of said audio signal and a second signal having high frequency components of said audio signal;

processing said first signal, while delaying said second signal by a first amount of time taken for said processing of said first signal to finish, to enhance first characteristics of said first signal such that said first signal after processing can still be aligned temporally with the said second signal;

and processing delayed said second signal while delaying processed said first signal by a second amount of time taken for said processing of delayed said second signal to finish, to enhance second characteristics of delayed said second signal such that delayed said second signal after processing can be aligned temporally with processed said first signal;

or

processing said delayed second signal, while delaying said first signal by a second amount of time taken for said processing of said second signal to finish, to enhance second characteristics of said second signal such that said second signal after processing can still be aligned temporally with the said first signal;

and processing delayed said first signal while delaying processed said second signal by a first amount of time taken for said processing of delayed said first signal to finish, to enhance first characteristics of delayed said first signal such that delayed said first signal after processing can be aligned temporally with processed said second signal;

combining processed and delayed said delayed first signal and processed and delayed said second signal to form a processed audio signal; and

generating a left-channel audio signal and a right-channel audio signal from said processed audio signal, wherein said left-channel audio signal is generated by adding a delayed and filtered version of said processed audio signal to said processed audio signal, said right-channel audio signal is generated by subtracting a delayed and filtered version of said processed audio signal from said processed audio signal.

2. The method as recited in claim 1, wherein said audio signal is produced from one of (i) a compressed audio file, (ii) a mono recording and (iii) a monaural sound.

3. The method as recited in claim 1, wherein said separating said audio signal is achieved through a phase-compensated crossover filter so that said first signal and said second signal remain synchronized in a time domain when said first signal and said second signal are recombined.

4. The method as recited in claim 3, wherein said processing said first signal further comprises modifying selectively said first signal by applying a mixture of even and odd harmonics of said low frequency components.

5. The method as recited in claim 4, wherein said processing said second signal further comprises modifying selectively said second signal by applying a mixture of even and odd harmonics of said high frequency components.

6. The method as recited in claim 1, wherein said first characteristics of said first signal enhanced by said processing said first signal include one or more of (i) a boosted bass, (ii) an optimized mix of even and odd harmonics for a smooth and rounder bass sound (iii) only-adjusted odd harmonics for sharper and more punchy bass.

7. The method as recited in claim 6, wherein said second characteristics of said second signal enhanced by said processing said second signal include one or more of (i) created harmonic series for a more intense and lively treble sound, (ii) higher clarity of treble ranges in said high frequency components, (iii) an optimized mix of even and odd harmonics for a warmer sound and (iv) only-adjusted odd harmonics for brighter treble.

8. An apparatus for enhancing the quality of an audio signal, said apparatus comprising:

a storage for said audio signal;

a bass maximizer, receiving said audio signal from said storage, enhancing low frequency components of said audio signal while delaying high frequency components of said audio signal by a first amount of time to ensure that said low and high frequency components are temporally aligned;

a harmonic exciter, coupled to said bass maximizer, enhancing said high frequency components of said audio signal while delaying said enhanced low frequency components by a second amount of time to ensure that said low and high frequency components are temporally aligned, wherein said harmonic exciter produces a processed audio signal; and

a quasi stereo module having first and second sound channels, said quasi stereo module coupled to said harmonic exciter and adding a delayed and filtered version of said processed audio signal to said processed audio signal for said first sound channel and subtracting a delayed and filtered version of said processed audio signal from said processed audio signal for said second sound channel.

9. The apparatus as recited in claim 8, wherein said bass maximizer comprises:

a first phase-compensated crossover filter receiving said audio signal from said storage and separating said audio signal into a first signal having said low frequency components of said audio signal and a second signal having said high frequency components of said audio signal;

a first circuit, coupled to said first phase-compensated crossover filter and receiving said first signal therefrom, comprising an amplifier and at least a first filter to enhance said low frequency components of said first signal; and

a compensation delay circuit, coupled to said first phase-compensated crossover filter, receiving and delaying said second signal by a first amount of time taken for said first circuit to process said first signal.

10. The apparatus as recited in claim 9, wherein said first filter has a distorting transfer function to provide an optimized mix of even and odd harmonics for a smoother and rounder bass.

11. The apparatus as recited in claim 9, wherein said first filter has a distorting transfer function to provide optimized odd harmonics only for a sharper and punchy bass.

12. The apparatus as recited in claim 9, wherein said first circuit further comprises a first limiter circuit coupled to said first filter and configured to maximize the volume of said first signal.

13. The apparatus as recited in claim 9, wherein said first circuit still further comprises a second order resonant high pass filter coupled to said limiter to position a resonant peak at a particular frequency and increase a bass effect of said first signal.

14. The apparatus as recited in claim 9, wherein said bass maximizer further comprises a first mixing circuit to combine processed said first signal and delayed said second signal to form a low-frequency processed audio signal.

15. The apparatus as recited in claim 14, wherein said harmonic exciter comprises

a second phase-compensated crossover filter receiving said low-frequency processed audio signal and separating said low-frequency processed audio signal into a third signal having low frequency components of said low-frequency processed audio signal and a fourth signal having high frequency components of said low-frequency processed audio signal;

a second circuit, coupled to said second phase-compensated crossover filter and receiving said third signal therefrom, comprising a second amplifier and at least a second filter to enhance said high frequency components of said low-frequency processed audio signal; and

a second compensation delay circuit, coupled to said second phase-compensated crossover filter, receiving and delaying said fourth signal by a second amount of time taken for said second circuit to process said third signal.

16. The apparatus as recited in claim 15, wherein said second circuit further comprises a second limiter circuit to maximize volume of said third signal so that lower amplitude high frequencies of said third signal can be contributed to an creation of new harmonic series for a more intense and lively treble enhancement.

17. The apparatus as recited in claim 16, wherein said second circuit has a distorting transfer function to provide one of (i) an optimized mix of even and odd harmonics for a warmer sound, and (ii) only-adjusted odd harmonics for brighter treble.

18. The apparatus as recited in claim 17, wherein said second circuit still comprises a pair of downsampling and upsampling circuits sandwiching said second filter, and an expander section circuit to expand original dynamics of said third signal to an enhanced treble.

19. The apparatus as recited in claim 18, wherein said harmonic exciter further comprises a second mixing circuit to combine processed said third signal and delayed said fourth signal to form a processed audio signal.

20. A computer readable medium containing program code for enhancing the quality of an audio signal, said computer readable medium comprising:

program code for separating said audio signal into a first signal having low frequency components of said audio signal and a second signal having high frequency components of said audio signal;

program code for processing said first signal, while delaying said second signal by a first amount of time taken for said program code for processing said first signal to finish, to enhance first characteristics of said first signal such that said first signal after processing can still be aligned temporally with the said delayed second signal;

and processing delayed said second signal while delaying processed said first signal by a second amount of time taken for said processing of delayed said second signal to finish, to enhance second characteristics of delayed said second signal such that delayed said second signal after processing can be aligned temporally with processed said first signal;

or

program code for processing said second signal, while delaying said first signal by a second amount of time taken for said program code for processing said second signal to finish, to enhance second characteristics of said second signal such that said second signal after processing can still be aligned temporally with the said delayed first signal;

and processing delayed said first signal while delaying processed said second signal by a first amount of time taken for said processing of delayed said first signal to finish, to enhance first characteristics of delayed said first signal such that delayed said first signal after processing can be aligned temporally with processed said second signal;

program code for combining processed and delayed said first signal and processed and delayed said second signal to form a processed audio signal; and

program code for generating a left-channel audio signal and a right-channel audio signal from said processed audio signal, wherein said left-channel audio signal is generated by adding a delayed and filtered version of said processed audio signal to said processed audio signal, said right-channel audio signal is generated by subtracting a delayed and filtered version of said processed audio signal from said processed audio signal.

21. The computer readable medium as recited in claim 20, wherein said program code for processing said first signal further comprises program code for modifying selectively said first signal by applying a mixture of even and odd harmonics of said low frequency components.

22. The computer readable medium as recited in claim 20, wherein said program code for processing said second signal further comprises program code for modifying selectively said second signal by applying a mixture of even and odd harmonics of said high frequency components.

23. The computer readable medium as recited in claim 22, wherein said second characteristics of said second signal enhanced by said program code for processing said second signal include one or more of (i) created harmonic series for a more intense and lively treble sound, (ii) higher clarity of treble ranges in said high frequency components, (iii) an optimized mix of even and odd harmonics for a warmer sound and (iv) only-adjusted odd harmonics for a brighter treble sound.

24. The computer readable medium as recited in claim 20, wherein said first characteristics of said first signal enhanced by said program code for processing said first signal include one or more of (i) a boosted bass, (ii) an optimized mix of even and odd harmonics for a smooth and rounder bass sound (iii) only-adjusted odd harmonics for sharper and more punchy bass.

25. The computer readable medium as recited in claim 20, wherein said program code for enhancing the quality of an audio signal is executed in a processor.

26. The computer readable medium as recited in claim 20, wherein said program code for enhancing the quality of an audio signal is transportable over a data network.