UTILIZATION OF FILTERING EFFECTS IN STEREO HEADPHONE DEVICES TO ENHANCE SPATIALIZATION OF SOURCE AROUND A LISTENER

• US 20070223751A1
• Filed: 02/28/2007
• Published: 09/27/2007
• Est. Priority Date: 09/16/1997
• Status: Active Grant

• Current Assignee: Adam Mckeag, Andrew Reilly, David Mcgrath, Glen Dickins, Richard Cartwright
• Original Assignee: Adam Mckeag, Andrew Reilly, David Mcgrath, Glen Dickins, Richard Cartwright
• Inventors: Reilly, Andrew, Dickins, Glen, McGrath, David, McKeag, Adam, Cartwright, Richard
• Granted Patent: US 7,539,319 B2
• Time in Patent Office: Days
• US Class Current: 381/310
• 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 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 3/004 For headphones
• CPC Class Codes: H04S 7/304 For headphones
• CPC Class Codes: H04S 7/306 For headphones

Abstract

An apparatus for creating, utilizing a pair of oppositely opposed headphone speakers, the sensation of a sound source being spatially distant from the area between the pair of headphones, the apparatus comprising: (a) a series of audio inputs representing audio signals being projected from an idealised sound source located at a spatial location relative to the idealised listener; (b) a first mixing matrix means interconnected to the audio inputs and a series of feedback inputs for outputting a predetermined combination of the audio inputs as intermediate output signals; (c) a filter system of filtering the intermediate output signals and outputting filtered intermediate output signals and the series of feedback inputs, the filter system including separate filters for filtering the direct response and short time response and an approximation to the reverberant response, in addition to the feedback response filtering for producing the feedback inputs; and (d) a second matrix mixing means combining the filtered intermediate output signals to produce left and right channel stereo outputs.

Claims

1. An apparatus comprising:

(a) a first mixer operable to accepting a set of audio inputs and a set of feedback inputs and to form a predetermined combination of said audio inputs as intermediate output signals, the audio inputs representing audio signals, each audio signal being projected from an idealized sound source located at a respective spatial sound source location relative to a listener location, the set of audio inputs including at least a left audio input and a right audio input said audio inputs puts;

(b) a filter system operable to filter said intermediate output signals to form filtered intermediate output signals, the filtering using one or more filters to account for the direct response of a room and one or more filters to account for an approximation to the reverberant response of the room, the filter system including feedback response filtering for producing said feedback inputs, such that the filtered intermediate output signals include filtered direct response signals, and filtered reverberant signals; and

(c) a second mixer operable to determine left and right channel stereo outputs for oppositely opposed headphones, the determining being by mixing of said filtered intermediate output signals,

such that a listener at the listener location and listening using the oppositely opposed headphones has the sensation of a sound source being spatially distant from the area between said pair of headphones.

2. An apparatus as recited in claim 1, wherein a predetermined number of the feedback inputs are also input to the second mixer.

3. An apparatus as recited in claim 1, wherein the feedback response filtering includes reverberation filtering.

4. An apparatus as recited in claim 3, wherein the reverberation filtering uses at least a sparse tap FIR filter, or a recursive algorithmic filter, or a full convolution FIR filter.

5. An apparatus as recited in claim 1, wherein the audio inputs include a surround sound set of signals.

6. An apparatus as recited in claim 5, wherein the feedback inputs are mixed with the frontal portions of the audio inputs only.

7. An apparatus as recited in claim 1, wherein the audio inputs includes audio inputs positioned in front of the listener location, and wherein the filter system includes a front sum filter filtering a summation of the audio inputs positioned in front of the listener location and the front sum filter includes substantially an approximation of the sum of a direct and shadowed head related transfer function for the front inputs.

8. An apparatus as recited in claim 1, wherein the audio inputs includes audio inputs positioned in front of the listener location, and wherein the filter system includes a front difference filter filtering a difference of the audio inputs positioned in front of the listener location and the front difference filter includes substantially an approximation of the difference of a direct and shadowed head related transfer function for the front inputs.

9. An apparatus as recited in claim 1, wherein the audio inputs includes audio inputs positioned in rear of the listener location, and wherein the filter system includes a rear sum filter filtering a summation of the audio inputs positioned in rear of the listener location and the rear sum filter includes substantially an approximation of the sum of a direct and shadowed head related transfer function for the rear inputs.

10. An apparatus as recited in claim 1, wherein the audio inputs includes audio inputs positioned in rear of the listener location, and wherein the filter system includes a rear difference filter filtering a difference of the audio inputs positioned in rear of the listener location and the rear difference filter includes substantially an approximation of the difference of a direct and shadowed head related transfer function for the rear inputs.

11. An apparatus as recited in claim 1, wherein the filter system includes a reverberation filter interconnected to the output of the first mixer and using a sum of the audio inputs.

12. An apparatus as recited in claim 1, wherein said apparatus is implemented using a skip protection processor unit located inside a CD-ROM player unit.

13. An apparatus as recited in claim 1, wherein said apparatus is implemented using a dedicated integrated circuit including a modified form of a digital to analog converter.

14. An apparatus as recited in claim 1, wherein said apparatus is implemented using a dedicated or programmable Digital Signal Processor.

15. An apparatus as recited in claim 1, wherein said apparatus operates on analog inputs by means of a DSP processor interconnected between an Analog to Digital Converter and a Digital to Analog Converter.

16. An apparatus as recited in claim 1, wherein said apparatus is implemented using a separately detachable external device connected intermediate of a sound output signal generator and said headphones said sound output signals being output in a digital form for processing by said external device.

17. An apparatus as recited in claim 1, wherein said apparatus is implemented using a separately detachable external device connected intermediate of a sound output signal generator and said headphones, said sound output signals being output in an analog form.

18. An apparatus as recited in claim 1, wherein the filter system uses filter coefficients, the apparatus further comprising:

a variable zoom control adapted to alter said filter coefficients in accordance with a control setting so as to alter a perceived distance of the location of the sound source.

19. An apparatus as recited in claim 1, wherein the approximation to the reverberant response of the room is weighted toward the front of the listener location.

20. A method comprising:

(a) accepting a set of audio inputs representing audio signals, each audio signal being projected from an idealized sound source located at a respective spatial sound source location relative to a listener location, the set of audio inputs including at least a left audio input and a right audio input;

(b) determining by mixing said audio inputs and a set of feedback inputs, the determining by mixing forming as intermediate output signals;

(c) filtering said intermediate output signals to form filtered intermediate output signals, the filtering using one or more filters to account for the direct response of a room and one or more filters to account for an approximation to the reverberant response of the room, the filtering including feedback response filtering for producing said feedback inputs, such that the filtered intermediate output signals include filtered direct response signals, and filtered reverberant signals; and

(d) determining left and right channel stereo outputs for oppositely opposed headphones, the determining being by mixing of said filtered intermediate output signals such that a listener at the listener location and listening using the oppositely opposed headphones has the sensation of a sound source being spatially distant from the area between said pair of headphones.

21. A method as recited in claim 20, wherein the determining in (d) includes mixing a predetermined number of the feedback inputs.

22. A method as recited in claim 20, wherein the feedback response filtering includes reverberation filtering.

23. A method as recited in claim 22, wherein the reverberation filtering uses at least a sparse tap FIR filter, or a recursive algorithmic filter, or a full convolution FIR filter.

24. A method as recited in claim 20, wherein the audio inputs include a surround sound set of signals.

25. A method as recited in claim 24, wherein the feedback inputs are mixed with the frontal portions of the audio inputs only.

26. A method as recited in claim 20, wherein the audio inputs includes audio inputs positioned in front of the listener location, and wherein the filter system includes a front sum filter filtering a summation of the audio inputs positioned in front of the listener location and the front sum filter includes substantially an approximation of the sum of a direct and shadowed head related transfer function for the front inputs.

27. A method as recited in claim 20, wherein the audio inputs includes audio inputs positioned in front of the listener location, and wherein the filtering of (c) includes front difference filtering to filter a difference of the audio inputs positioned in front of the listener location and the front difference filter, the front difference filtering using substantially an approximation of the difference of a direct and shadowed head related transfer function for the front inputs.

28. A method as recited in claim 20, wherein the audio inputs includes audio inputs positioned in rear of the listener location, and wherein the filtering of (c) includes rear sum filtering to filter a summation of the audio inputs positioned in rear of the listener location, the rear sum filtering using substantially an approximation of the sum of a direct and shadowed head related transfer function for the rear inputs.

29. A method as recited in claim 20, wherein the audio inputs includes audio inputs positioned in rear of the listener location, and wherein the filtering of (c) includes rear difference filtering to filter a difference of the audio inputs positioned in rear of the listener location, the rear difference filtering using substantially an approximation of the difference of a direct and shadowed head related transfer function for the rear inputs.

30. A method as recited in claim 20, wherein the filtering of (c) includes reverberation filtering using a sum of the audio inputs.

31. A method as recited in claim 20, wherein the filtering of (c) is performed using a skip protection processor unit located inside a CD-ROM player unit.

32. A method as recited in claim 31, further comprising using a variable zoom control to alter a perceived distance of the binaural response of the room in which the listener is located.

33. A method as recited in claim 20, wherein the filtering of (c) is performed using a dedicated integrated circuit including a modified form of a digital to analog converter.

34. A method as recited in claim 20, wherein the filtering of (c) is performed using a dedicated or programmable Digital Signal Processor.

35. A method as recited in claim 20, wherein the filtering of (c) is performed on analog inputs by a DSP processor interconnected between an Analog to Digital Converter and a Digital to Analog Converter.

36. A method as recited in claim 20, wherein the filtering of (c) is performed on stereo output signals on a separately detachable external device connected intermediate of a sound output signal generator and said headphones said sound output signals being output in a digital form for processing by said external device.

37. A method as recited in claim 20, wherein the filtering of (c) is performed on stereo output signals on a separately detachable external device connected intermediate of a sound output signal generator and said headphones, said sound output signals being output in an analog form.