Audio signal processing

• US 7,720,240 B2
• Filed: 04/03/2007
• Issued: 05/18/2010
• Est. Priority Date: 04/03/2006
• Status: Active Grant

• Current Assignee: DTS, Inc. (Adeia Inc.)
• Original Assignee: SRS Labs Incorporated (Adeia Inc.)
• Inventors: Wang, Wen
• Primary Examiner(s): Chin; Vivian
• Assistant Examiner(s): Tran; Con P
• Application Number:
  US11/696,128
• Publication Number:
  US 20070230725A1
• Time in Patent Office: 1,141 Days
• Field of Search: 381/310, 381/309, 381/260, 381/74, 381/17, 381/1, 381/26, 381/300
• US Class Current: 381/309
• 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 2400/05 Generation or adaptation of centre channel in multi-channel audio systems
• CPC Class Codes: H04S 2420/01 Enhancing the perception of the sound image or of the spatial distribution using head related transfer functions [HRTF's] or equivalents thereof, e.g. interaural time difference [ITD] or interaural level difference [ILD]
• CPC Class Codes: H04S 3/002 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 3/004 For headphones
• CPC Class Codes: H04S 3/02 of the matrix type, i.e. in which input signals are combined algebraically, e.g. after having been phase shifted with respect to each other
• CPC Class Codes: H04S 5/02 of the pseudo four-channel type, e.g. in which rear channel signals are derived from two-channel stereo signals

Abstract

Systems and methods of processing audio signals are described. The audio signals comprise information about spatial position of a sound source relative to a listener. At least one audio filter generates two filtered signals for each of audio signal. The two filtered signals are mixed with other filtered signals from other audio signals to create a right output audio channel and a left audio output channel, such that the spatial position of the sound source is perceptible from the right and left audio output channels.

Claims

1. A method for processing audio signals for a set of headphones, the method comprising:

receiving a plurality of audio signal inputs, each audio signal input comprising information about a spatial position of a sound source relative to a listener;

mixing two or more inputs of the plurality of audio signal inputs to produce at least one mixed audio signal;

providing the at least one mixed audio signal to first set of positional filters, the first set of positional filters configured to selectively emphasize one or more location-relevant portions of a head-related transfer function (HRTF), the first set of positional filters being implemented as one or more first infinite impulse response (IIR) filters, the first set of positional filters comprising two or more of the following;

a first positional filter comprising first component filters, the first component filters comprising a first band stop filter, a first band pass filter, and a first high pass filter,

a second positional filter comprising second component filters, the second component filters comprising a second band stop filter, a third band stop filter, and a fourth band stop filter,

a third positional filter comprising third component filters, the third component filters comprising a fifth band stop filter, a second band pass filter, and a sixth band stop filter, and

a fourth positional filter comprising fourth component filters, the fourth component filters comprising a seventh band stop filter, a third band pass filter, and an eighth band stop filter;

passing at least some of the audio signal inputs as unmixed audio signals to a second set of positional filters, the second set of positional filters comprising a second IIR filter, wherein the mixed and unmixed audio signals are arranged such that each audio signal input is provided in mixed and unmixed form to both the first and second sets of positional filters;

applying the first set of positional filters to the mixed audio signals and the second set of positional filters to the unmixed audio signals to create a plurality of left channel filtered signals and a plurality of right channel filtered signals respectively; and

downmixing the plurality of left channel filtered signals into a left audio output channel and downmixing the plurality of right channel filtered signals into a right audio output channel, such that the spatial positions of the plurality of sound sources are perceptible from the left and right output channels of a set of headphones.

2. The method of claim 1 further comprising mixing the center input with one or more of the left and right inputs.

3. The method of claim 1 further comprising mixing the center surround input with one or more of the left surround and right surround inputs.

4. The method of claim 1, further comprising delaying one or more of the audio signal inputs.

5. The method of claim 1, wherein the spatial position comprises a virtual speaker location in a surround-sound system.

6. A method for processing audio signals, the method comprising:

receiving multiple audio signals, the multiple audio signals comprising information about spatial position of sound sources relative to a listener;

applying two or more audio filters to each of the multiple audio signals so as to yield two corresponding filtered signals for each of the multiple audio signals, the two or more audio filters configured to selectively emphasize one or more location-relevant portions of a head-related transfer function (HRTF), the two or more audio filters being implemented as one or more first infinite impulse response (IIR) filters, the two or more audio filters comprising two more of the following;

a first positional filter comprising first component filters, the first component filters comprising a first band stop filter, a first band pass filter, and a first high pass filter,

a second positional filter comprising second component filters, the second component filters comprising a second band stop filter, a third band stop filter, and a fourth band stop filter,

a third positional filter comprising third component filters, the third component filters comprising a fifth band stop filter, a second band pass filter, and a sixth band stop filter, and

a fourth positional filter comprising fourth component filters, the fourth component filters comprising a seventh band stop filter, a third band pass filter, and an eighth band stop filter; and

mixing the filtered signals to create a left audio output and a right audio output, wherein the spatial position of the sound sources are perceptible from the right and left audio outputs.

7. The method of claim 6, wherein the two or more audio filters comprise two audio filters, wherein each audio filter provides one of the two filtered signals.

8. The method of claim 6, wherein the spatial position comprises a virtual speaker location in a surround-sound system.

9. An apparatus for processing audio signals, the apparatus comprising:

multiple audio signal inputs, each of the multiple audio signal inputs comprising information about spatial position of a sound source relative to a listener;

a plurality of positional filters, wherein each of the multiple audio signal inputs is provided to two or more of the positional filters to create at least one right channel filtered signal and at least one left channel filter signal for each audio signal, the plurality of positional filters configured to selectively emphasize one or more location-relevant portions of a head-related transfer function (HRTF), the first positional filters being implemented as one or more first infinite impulse response (IIR) filters, the plurality of positional filters comprising two or more of the following;

a first positional filter comprising first component filters, the first component filters comprising a first band stop filter, a first band pass filter, and a first high pass filter,

a second positional filter comprising second component filters, the second component filters comprising a second band stop filter, a third band stop filter, and a fourth band stop filter,

a third positional filter comprising third component filters, the third component filters comprising a fifth band stop filter, a second band pass filter, and a sixth band stop filter, and

a fourth positional filter comprising fourth component filters, the fourth component filters comprising a seventh band stop filter, a third band pass filter, and an eighth band stop filter; and

a downmixer configured to downmix the right channel filtered signals into a right audio output channel and downmix the left channel filtered signals into a left audio output channel, such that the spatial positions of the plurality of sound sources are perceptible from the right and left output channels.

10. The apparatus of claim 9, wherein each audio signal input is provided to two of the plurality of positional filters.

11. The apparatus of claim 9, wherein the spatial position comprises a virtual speaker location in a surround-sound system.

12. An apparatus for processing audio signals, the apparatus comprising:

means for receiving an audio signal, the audio signal comprising information about spatial position of a sound source relative to a listener;

means for selecting two or more audio filters configured to selectively emphasize one or more location-relevant portions of a head-related transfer function (HRTF), the two or more audio filters being implemented as one or more first infinite impulse response (IIR) filters, the two or more audio filters comprising two more of the following;

a first positional filter comprising first component filters, the first component filters comprising a first band stop filter, a first band pass filter, and a first high pass filter,

a second positional filter comprising second component filters, the second component filters comprising a second band stop filter, a third band stop filter, and a fourth band stop filter,

a third positional filter comprising third component filters, the third component filters comprising a fifth band stop filter, a second band pass filter, and a sixth band stop filter, and

a fourth positional filter comprising fourth component filters, the fourth component filters comprising a seventh band stop filter, a third band pass filter, and an eighth band stop filter;

means for applying the two or more audio filters to the audio signal so as to yield two corresponding filtered signals; and

means for providing one of the filtered signals to a left audio channel and the other filtered signal to a right audio channel, such that the spatial position of the sound source is perceptible from each channel.