Apparatus and Method for Generating Filter Characteristics

• US 20110103620A1
• Filed: 04/09/2009
• Published: 05/05/2011
• Est. Priority Date: 04/09/2008
• Status: Active Grant

• Current Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Original Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Inventors: Strauss, Michael, Korn, Thomas
• Granted Patent: US 9,066,191 B2
• Time in Patent Office: Days
• US Class Current: 381/150
• CPC Class Codes: H04R 1/403 loud-speakers
• CPC Class Codes: H04R 3/12 for distributing signals to two or more loudspeakers specially adapted for hearing aids H04R25/407
• CPC Class Codes: H04S 3/00 Systems employing more than two channels, e.g. quadraphonic H04S5/00, H04S7/00 take precedence
• CPC Class Codes: H04S 7/303 Tracking of listener position or orientation

Abstract

An apparatus for generating filter characteristics for filters connectible to at least three loudspeakers at defined locations with respect to a sound reproduction zone includes an impulse response reverser for time-reversing impulse responses associated to the loudspeakers to obtain time-reversed impulse responses. The apparatus furthermore includes an impulse response modifier for modifying the impulse responses or the time-reversed impulse responses such that impulse response portions occurring before a maximum of a time-reversed impulse response are reduced in amplitude to obtain the filter characteristics for the filters.

Claims

1. Apparatus for generating filter characteristics for filters connectible to at least three loudspeakers at defined locations with respect to a sound reproduction zone, comprising:

an impulse response reverser for time-reversing impulse responses associated to the loudspeakers to acquire time-reversed impulse responses, wherein each impulse response describes a sound transmission channel between a location within the sound reproduction zone and a loudspeaker, which has the impulse response associated therewith; and

an impulse response modifier for modifying the time-reversed impulse responses or the impulse responses associated to the loudspeakers before inversion, such that impulse response portions occurring before a maximum of a time-reversed impulse response are reduced in amplitude to acquire the filter characteristics for the filters.

2. Apparatus in accordance with claim 1 in which the impulse response modifier is operative to reduce a portion of the time-reversed impulse response or the impulse response before time-reversal, the portion occurring immediately before the maximum of the time-reversed impulse response in accordance with a monotonically decreasing function.

3. Apparatus in accordance with claim 2, in which the monotonically increasing function is derived from a premasking characteristic of the human hearing system.

4. Apparatus in accordance with claim 1, in which the impulse response modifier is operative to modify such that the modified time-reversed impulse response comprises amplitude values below 50 percent of the maximum at a time distance of between 20 ms and 50 ms to a time of the maximum of the impulse response.

5. Apparatus in accordance with claim 1, further comprising:

a detector for detecting portions of the impulse responses or time-reversed impulse responses, which cause useful reflections or which cause pre-echos at the sound focusing location, wherein the impulse response modifier is operative to modify, in response to a detector output, so that portions in the impulse response not related to useful reflections are attenuated.

6. Apparatus in accordance with claim 1, in which the impulse response modifier is operative to not perform a modification which would result in a modification of the time-reversed impulse response subsequent in time to a time of the maximum.

7. Apparatus in accordance with claim 1, in which the impulse response modifier is operative to determine local peaks in the time-reversed impulse response or the impulse response before time-reversal, and to not attenuate the peaks and to attenuate portions between two peaks or to attenuate the peaks with a first degree and to attenuate the portion between the peaks with a second degree greater than the first degree.

8. Apparatus in accordance with claim 7, in which the impulse response modifier is operative to attenuate the portions between the peaks by applying a first time constant comprising a first value before a peak with respect to the time-reversed impulse response and by applying a second time constant comprising a second value subsequent to the peak with respect to the time-reversed impulse response, the second value being greater than the first value.

9. Apparatus in accordance with claim 1, in which the sound reproduction zone comprises at least two spatially different zone focusing locations,

in which the impulse response reverser is operative to time-reverse an impulse response for each sound focusing location to each loudspeaker, and

wherein the impulse response modifier is operative to modify each impulse response or each time-reversed impulse response individually, before modified impulse responses or modified time-reversed impulse responses for sound transmission channels to a speaker are combined, or

wherein a combined impulse response or time-reversed impulse response is derived by combining the impulse responses or time-reversed impulse responses associated with sound transmission channels to the same loudspeaker, wherein the impulse response modifier is operative to perform a modification using the combined impulse response.

10. Apparatus in accordance with claim 9, in which the sound focusing locations comprise a distance approximating a distance between ears of a human head or a human head model.

11. Apparatus in accordance with claim 9, in which at least three sound focusing locations are distributed in a predefined sound focusing location area being smaller than the sound reproduction zone defined by the loudspeakers, wherein the sound focusing locations are so close to each other that a specified portion between the sound focusing locations comprises a sound energy, which is higher than outside the sound focusing area by at least 50 percent.

12. Apparatus in accordance with claim 1, further comprising a processor comprising a numerical optimizer adapted to optimize starting values for filter coefficients in order to acquire an optimum matching of an actual sound energy focusing characteristic to a desired sound focusing characteristic at one or more sound focusing locations in an iterative procedure, and

wherein modified and reversed impulse responses are used as the starting values for the iterative procedure.

13. Method of generating filter characteristics for filters connectible to at least three loudspeakers at defined locations with respect to a sound reproduction zone, comprising:

time-reversing impulse responses associated to the loudspeakers to acquire time-reversed impulse responses, wherein each impulse response describes a sound transmission channel between a location within the sound reproduction zone and a loudspeaker, which has the impulse response associated therewith; and

modifying the time-reversed impulse responses or the impulse responses associated to the loudspeakers before inversion, such that impulse response portions occurring before a maximum of a time-reversed impulse response are reduced in amplitude to acquire the filter characteristics for the filters.

14. Computer program comprising a program code for performing, when running on a computer, the method of generating filter characteristics for filters connectible to at least three loudspeakers at defined locations with respect to a sound reproduction zone, the method comprising:

time-reversing impulse responses associated to the loudspeakers to acquire time-reversed impulse responses, wherein each impulse response describes a sound transmission channel between a location within the sound reproduction zone and a loudspeaker, which has the impulse response associated therewith; and

modifying the time-reversed impulse responses or the impulse responses associated to the loudspeakers before inversion, such that impulse response portions occurring before a maximum of a time-reversed impulse response are reduced in amplitude to acquire the filter characteristics for the filters.

15. Sound reproduction system, comprising:

an apparatus for generating filter characteristics for filters connectible to at least three loudspeakers at defined locations with respect to a sound reproduction zone, the apparatus comprising;

an impulse response reverser for time-reversing impulse responses associated to the loudspeakers to acquire time-reversed impulse responses, wherein each impulse response describes a sound transmission channel between a location within the sound reproduction zone and a loudspeaker, which has the impulse response associated therewith; and

an impulse response modifier for modifying the time-reversed impulse responses or the impulse responses associated to the loudspeakers before inversion, such that impulse response portions

occurring before a maximum of a time-reversed impulse response are reduced in amplitude to acquire the filter characteristics for the filters; and

a plurality of programmable filters programmed to the filter characteristics determined by the apparatus for generating the filter characteristics;

a plurality of loudspeakers at predefined locations, wherein each loudspeaker is connected to one of the plurality of filters; and

an audio source connected to the filters.