SYSTEM FOR INCREASING PERCEIVED LOUDNESS OF SPEAKERS

• US 20110038490A1
• Filed: 08/11/2009
• Published: 02/17/2011
• Est. Priority Date: 08/11/2009
• Status: Active Grant

• Current Assignee: DTS, Inc. (Adeia Inc.)
• Original Assignee: SRS Labs Incorporated (Adeia Inc.)
• Inventors: Maling, Robert C. III, Yang, Sarah, Oliver, Richard J.
• Granted Patent: US 8,538,042 B2
• Time in Patent Office: Days
• US Class Current: 381/103
• CPC Class Codes: H03G 5/165 Equalizers; Volume or gain control in limited frequency bands
• CPC Class Codes: H03G 7/002 in untuned or low-frequency amplifiers, e.g. audio amplifiers H03G7/007, H03G7/001, H03G7/008, H03G7/02, H03G7/06 take precedence
• CPC Class Codes: H04R 3/04 for correcting frequency response

Abstract

A system can be provided for increasing loudness of an audio signal to present a perceived loudness to a listener that is greater than a loudness provided natively by a loudspeaker. The system can include one or more of the following: a frequency suppressor, a loudness adjuster, an equalizer, and a distortion control module. The frequency suppressor can increase headroom in the audio signal by filtering out low and/or high frequencies. The loudness adjuster can calculate a loudness of the audio signal and apply a gain to the audio signal to increase the loudness. The equalizer can further increase headroom by attenuating portions of a passband of the loudspeaker'"'"'s frequency response. The distortion control module can induce partial harmonic distortion in the audio signal to further increase loudness.

Claims

1. A method of increasing perceived loudness of an audio signal, the method comprising:

receiving an electronic audio signal;

processing the electronic audio signal with a frequency suppressor using one or more processors, the frequency suppressor configured to filter one or both of low frequencies and high frequencies of the electronic audio signal to produce a filtered audio signal, such that the filtered audio signal has increased headroom;

estimating a loudness of the filtered audio signal at least in part by processing the filtered audio signal with one or more loudness filters configured to approximate a human hearing system to produce an estimated loudness of the audio signal; and

computing one or more gains to be applied to the filtered audio signal based at least in part on the estimated loudness; and

increasing loudness of the filtered audio signal by applying the one or more gains to the filtered audio signal.

2. The method of claim 1, wherein said processing the electronic audio signal with a frequency suppressor comprises filtering frequencies that are less reproducible by a given speaker.

3. The method of claim 1, further comprising providing additional headroom to the electronic audio signal by applying an equalization filter to the electronic audio signal, wherein the equalization filter is operative to attenuate passband areas of the electronic audio signal.

4. The method of claim 1, wherein the one or more loudness filters approximate one or more gammatone filters.

5. A system for increasing a loudness of an audio signal, the system comprising:

a frequency suppressor comprising one or more filters configured to increase headroom in an electronic audio signal by filtering one or both of low frequencies and high frequencies of the electronic audio signal to produce a filtered audio signal having a greater headroom than the electronic audio signal; and

a loudness adjuster comprising;

a loudness analyzer configured to estimate with one or more processors a loudness of the filtered audio signal and to compare the calculated loudness with a loudness reference level, and

a gain control module operative to compute one or more gains based at least partly on a difference between the calculated loudness and the loudness reference level and to increase a loudness of the filtered audio signal by applying the one or more gains to the filtered audio signal to produce an amplified audio signal.

6. The system of claim 6, further comprising an equalizer operative to attenuate passband areas of a frequency response of a speaker that are less reproducible by the speaker.

7. The system of claim 6, further comprising a distortion control module configured to further increase the loudness in the filtered audio signal by inducing selected distortion in the filtered audio signal.

8. The system of claim 7, wherein the distortion control module induces selected distortion by introducing selected harmonics in the filtered audio signal.

9. A computer-readable storage medium having instructions stored thereon that cause one or more processors to perform a method of increasing perceived loudness of an audio signal, the method comprising:

receiving an electronic audio signal;

estimating a loudness of the electronic audio signal at least in part by processing the electronic audio signal with one or more loudness filters configured to approximate a human hearing system to produce an estimated loudness of the audio signal; and

computing one or more gains to be applied to the electronic audio signal based at least in part on the estimated loudness;

increasing perceived loudness of the electronic audio signal by applying the one or more gains to the electronic audio signal to produce an amplified audio signal; and

increasing signal energy by inducing partial saturation in the amplified audio signal, said inducing comprising applying to the amplified audio signal a nonlinear transformation derived from a combination of harmonics.

10. The computer-readable storage medium of claim 9, wherein said inducing partial saturation comprises indexing samples of the amplified audio signal into a sum-of-sines table.

11. The computer-readable storage medium of claim 9, wherein the harmonics comprise odd harmonics.

12. The computer-readable storage medium of claim 11, wherein the harmonics comprise a first harmonic, a third harmonic, a fifth harmonic, a seventh harmonic, and a ninth harmonic.

13. A method of reducing clipping in an audio signal, the method comprising:

receiving an input audio signal;

providing a sum-of-sines data structure, the sum-of-sines data structure comprising values generated from a sum of lower order harmonics; and

using the sum-of-sines data structure with one or more processors to map the input audio signal to an output audio signal, such that at least some of the lower-order harmonics are added to the input audio signal, wherein at least a portion of the output audio signal has a greater energy than the input audio signal.

14. The method of claim 13, further comprising generating the sum-of-sine data structure from fewer harmonics than are present in a fully saturated signal.

15. The computer-readable storage medium of claim 13, wherein the harmonics comprise odd harmonics.

16. The computer-readable storage medium of claim 13, wherein the harmonics comprise even harmonics.

17. The computer-readable storage medium of claim 13, further comprising generating the sum-of-sines data structure at least in part by populating a first data structure with one period of a sine wave, populating a second data structure with multiple periods of the sine wave, and combining values in the first and second data structures.

18. The computer-readable storage medium of claim 13, wherein the sum-of-sines data structure comprises one quarter of a composite sum-of-sines wave.

19. A system for increasing a loudness of an audio signal produced by a loudspeaker to present a perceived loudness to a listener that is greater than a loudness produced natively by the loudspeaker, the system comprising:

a frequency suppressor comprising one or more filters configured to increase headroom in an electronic audio signal by filtering low and high frequencies of the electronic audio signal to produce a first filtered audio signal, the low and high frequencies being substantially unreproducible by the speaker;

a loudness adjuster comprising;

a loudness analyzer configured to calculate with one or more processors a loudness of the first filtered audio signal at least in part by processing the first filtered audio signal with one or more loudness filters configured to approximate a human hearing system, the loudness analyzer further configured to compare the calculated loudness with a loudness reference level, and

a gain control module operative to compute one or more gains to be applied to the first filtered audio signal and to apply the one or more gains to the first filtered audio signal to produce an amplified audio signal, said computing the one or more gains being based at least partly on a difference between the calculated loudness and the loudness reference level;

a distortion control module configured to induce partial harmonic distortion in the first filtered audio signal by at least mapping one or more samples of the first filtered audio signal to one or more values stored in a sum-of-sines table, the sum-of-sines table being generated from a sum of lower-order harmonics.

20. The system of claim 19, further comprising an equalization filter configured to further increase headroom in the electronic audio signal, wherein the equalization filter is operative to attenuate passband areas of the electronic audio signal.

21. The system of claim 19, wherein the frequency suppressor comprises a high pass filter and a low pass filter each having a cutoff frequency that depends at least partly on a characteristic of a loudspeaker.

22. The system of claim 21, wherein the lower-order harmonics comprise first, third, fifth, seventh, and ninth harmonics.

23. A method of increasing loudness of an audio signal, the method comprising:

receiving an electronic audio signal;

processing the electronic audio signal with a frequency suppressor using one or more processors, the frequency suppressor configured to filter one or both of low and high frequencies of the electronic audio signal to produce a filtered audio signal, such that the filtered audio signal has increased headroom over the electronic audio signal, wherein the frequency suppressor is not a crossover filter;

deriving one or more gains to apply to the filtered audio signal based at least in part on the increased headroom; and

applying one or more gains to the filtered audio signal to increase a loudness of the audio signal.

24. The method of claim 23, wherein said processing the electronic audio signal with a frequency suppressor comprises filtering frequencies that are less reproducible by a given speaker.

25. The method of claim 23, wherein said deriving one or more gains comprises estimating a loudness of the filtered audio signal and comparing the estimated loudness with a reference level.

26. A method of increasing loudness of an audio signal, the method comprising:

receiving an electronic audio signal;

providing an equalization filter comprising a frequency response configured to attenuate passband areas of the electronic audio signal, the passband areas corresponding to areas of a frequency response of a speaker that are less reproducible by a loudspeaker;

applying the equalization filter to the electronic audio signal using one or more processors to increase headroom in the electronic audio signal; and

using the increased headroom in the electronic audio signal to increase loudness of the electronic audio signal.

27. The method of claim 26, further comprising processing the electronic audio signal with a frequency suppressor, the frequency suppressor configured to filter one or both of low and high frequencies of the electronic audio signal to produce a filtered audio signal, such that the filtered audio signal has additional headroom.

28. The method of claim 26, wherein using the increased headroom in the electronic audio signal to increase loudness of the electronic audio signal comprises applying one or more gains to the electronic audio signal.

29. The method of claim 28, further comprising calculating the one or more gains based at least partly on an estimated loudness of the electronic audio signal.

30. The method of claim 29, further comprising inducing partial harmonic distortion in the electronic audio signal to further increase loudness of the electronic audio signal.