Adaptive room equalization using a speaker and a handheld listening device

• US 9,538,308 B2
• Filed: 03/13/2014
• Issued: 01/03/2017
• Est. Priority Date: 03/14/2013
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Isaac, Ronald N.
• Primary Examiner(s): Laekemariam, Yosef K
• Application Number:
  US14/775,585
• Publication Number:
  US 20160029142A1
• Time in Patent Office: 1,027 Days
• Field of Search: 381/58, 381/59, 381/89, 381/96, 381/111, 381/303, 381/320, 381/94.2, 381/358, 381/386, 381/103
• US Class Current: 1/1
• CPC Class Codes: H04S 2400/01 Multi-channel, i.e. more than two input channels, sound reproduction with two speakers wherein the multi-channel information is substantially preserved
• CPC Class Codes: H04S 2400/15 Aspects of sound capture and related signal processing for recording or reproduction
• CPC Class Codes: H04S 2420/07 Synergistic effects of band splitting and sub-band processing
• CPC Class Codes: H04S 7/301 Automatic calibration of stereophonic sound system, e.g. with test microphone
• CPC Class Codes: H04S 7/307 Frequency adjustment, e.g. tone control H04S7/301 takes precedence

Abstract

A loudspeaker that measures the impulse response of a listening area is described. The loudspeaker may output sounds corresponding to a segment of an audio signal. The sounds are sensed by a listening device proximate to a listener and transmitted to the loudspeaker. The loudspeaker includes an adaptive filter that estimates the impulse response of the listening area based on the signal segment. An error unit analyzes the estimated impulse response together with the sensed audio signal received from the listening device to determine the accuracy of the estimate. New estimates may be generated by the adaptive filter until an accuracy level is achieved for the signal segment. A processor may utilize one or more estimated impulse responses corresponding to various signal segments that cover a defined frequency spectrum for adjusting the audio signal to compensate for the impulse response of the listening area. Other embodiments are also described.

Claims

1. A method for adjusting sound emitted by a loudspeaker in a room, comprising:

driving one or more transducers to emit sounds based on a first segment of an audio signal;

characterizing spectral characteristics of the first segment;

receiving, by the loudspeaker, a sensed audio signal from a handheld device, wherein the sensed audio signal represents the sounds emitted by the one or more transducers corresponding to the first segment of the audio signal;

estimating, by an adaptive filter, an impulse response for the room based on the first segment of the audio signal;

determining an error value for the estimated impulse response based on the sensed audio signal;

storing the impulse response and the spectral characteristics of the first segment, in response to the error value being below a predefined error level and the impulse response being within a tolerance level of one or more previously stored impulse responses; and

processing a second segment of the audio signal based on a given one or more previously stored impulse responses, in response to determining that previously stored spectral characteristics, corresponding to the given one or more previously stored impulse responses, cover a predefined spectrum.

2. The method of claim 1, further comprising:

correlating the first segment with the sensed audio signal to determine a delay time between the first segment and the sensed audio signal; and

delaying the first segment by the delay time to generate a delayed first segment, wherein the estimating the impulse response is performed with the delayed first segment.

3. The method of claim 1, further comprising:

determining that the handheld device is being held near an ear of a listener;

sensing, by the handheld device in response to determining the handheld device is being held near the ear of the listener, the sounds emitted by the one or more transducers; and

transmitting, by the handheld device, the sensed audio signal to the loudspeaker.

4. The method of claim 3, wherein sensing that the handheld device is being held near the ear of the listener is performed based on inputs from one or more of a capacitive sensor, an accelerometer, and a camera.

5. The method of claim 1, further comprising:

combining two or more previously stored impulse responses whose associated spectral characteristics collectively cover the predefined spectrum, wherein processing the second segment is performed based on the combined two or more previously stored impulse responses.

6. The method of claim 1, further comprising:

estimating, in response to the error value being equal or above the predefined error level, a new impulse response for the room based on the first segment and the error value;

determining a new error value for the new impulse response; and

storing the new impulse response and the spectral characteristics of the first segment, in response to the new error value of the new impulse response being below the predefined error level and the new impulse response being within the tolerance level of one or more previously stored impulse responses.

7. The method of claim 1, wherein the tolerance level is a measured deviation between the impulse response and the one or more previously stored impulse responses.

8. The method of claim 1, wherein the first segment and the second segment are time divisions of the audio signal.

9. The method of claim 1, wherein the audio signal represents a channel of a piece of multichannel audio content.

10. A loudspeaker, comprising:

a transducer for emitting sounds corresponding to a first segment of an audio signal;

a wireless controller for receiving a sensed audio signal from a listening device, wherein the sensed audio signal represents the sounds emitted by the transducer corresponding to the first segment of the audio signal

an adaptive filter for estimating an impulse response of a room in which the loudspeaker is located based on the first segment of the audio signal;

an error unit for determining an error value for the estimated impulse response of the room based on the sensed audio signal, wherein the controller stores the impulse response and spectral characteristics of the first segment in response to (i) the error value being below a predefined error level and (ii) the impulse response being within a tolerance level of one or more previously stored impulse responses; and

a content processor for processing a second segment of the audio signal based on a given one or more previously stored impulse responses, in response to determining that previously stored spectral characteristics, corresponding to the given one or more previously stored impulse responses, cover a predefined spectrum.

11. The loudspeaker of claim 10, further comprising:

a spectrum analyzer for characterizing the first segment and generating the spectral characteristics of the first segment.

12. The loudspeaker of claim 10, further comprising:

a cross-correlation unit for correlating the first segment with the sensed audio signal to determine a delay time between the first segment and the sensed audio signal; and

a delay unit for delaying the first segment by the delay time to generate a delayed first segment, wherein the adaptive filter estimates the impulse response of the room using the delayed first segment.

13. The loudspeaker of claim 10, further comprising:

a coefficient analyzer for combining two or more previously stored impulse responses whose associated spectral characteristics collectively cover the predefined spectrum, wherein the content processor processes the second segment based on the combined two or more previously stored impulse responses.

14. The loudspeaker of claim 10, wherein the adaptive filter estimates a new impulse response for the room based on the first segment and the error value, in response to the error value being equal or above the predefined error level.

15. The loudspeaker of claim 10, wherein the tolerance level is a measured deviation between the impulse response and the one or more previously stored impulse responses.

16. The loudspeaker of claim 10, wherein the adaptive filter is a linear mean square filter.

17. An article of manufacture for adjusting sound emitted by a loudspeaker in a room, comprising:

a machine-readable storage medium that stores instructions which, when executed by a processor in a computer,

characterize spectral characteristics of a first segment of an audio signal;

receive a sensed audio signal from a handheld device, wherein the sensed audio signal represents sounds emitted by one or more transducers corresponding to the first segment of the audio signal;

estimate, by an adaptive filter, an impulse response for the room based on the first segment of the audio signal;

determine an error value for the estimated impulse response based on the sensed audio signal;

store the impulse response and the spectral characteristics of the first segment in response to the error value being below a predefined error level and the impulse response being within a tolerance level of one or more previously stored impulse responses; and

process a second segment of the audio signal based on a given one or more previously stored impulse responses, in response to determining that previously stored spectral characteristics, corresponding to the given one or more previously stored impulse responses, cover a predefined spectrum.

18. The article of manufacture of claim 17, wherein the machine-readable storage medium stores additional instructions which, when executed by the processor in the computer,

correlate the first segment with the sensed audio signal to determine a delay time between the first segment and the sensed audio signal;

and

delay the first segment by the delay time to generate a delayed first segment, wherein the estimating the impulse response is performed with the delayed first segment.

19. The article of manufacture of claim 17, wherein the machine-readable storage medium stores additional instructions which, when executed by the processor in the computer,

combine two or more previously stored impulse responses whose associated spectral characteristics collectively cover the predefined spectrum, wherein processing the second segment is performed based on the combined two or more previously stored impulse responses.

20. The article of manufacture of claim 17, wherein the machine-readable storage medium stores additional instructions which, when executed by the processor in the computer,

estimate, in response to the error value being equal or above the predefined error level, a new impulse response for the room based on the first segment and the error value;

determine a new error value for the new impulse response; and

store the new impulse response and the spectral characteristics of the first segment, in response to the new error value of the new impulse response being below the predefined error level and the new impulse response being within the tolerance level of one or more previously stored impulse responses.

21. The article of manufacture of claim 17, wherein the tolerance level is a measured deviation between the impulse response and the one or more previously stored impulse responses.

22. The article of manufacture of claim 17, wherein the first segment and the second segment are time divisions of the audio signal.

23. The article of manufacture of claim 17, wherein the audio signal represents a channel of a piece of multichannel audio content.