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

• US 20070172086A1
• Filed: 03/20/2007
• Published: 07/26/2007
• 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: McGrath, David, Reilly, Andrew, McKeag, Adam, Dickins, Glen, Cartwright, Richard
• Granted Patent: US 7,536,021 B2
• Time in Patent Office: Days
• 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 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 for creating, utilizing a pair of oppositely opposed headphones, the sensation of a sound source being spatially distant from the area between said pair of headphones, said apparatus comprising:

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

(b) a first mixing matrix means interconnected to said audio inputs and a series of feedback inputs for outputting a predetermined combination of said audio inputs as intermediate output signals;

(c) a filter system for filtering said intermediate output signals and outputting filtered intermediate output signals and said series of feedback inputs, said filter system including 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

(d) a second matrix mixing means combining said filtered intermediate output signals to produce left and right channel stereo outputs.

2. An apparatus as claimed in claim 1 wherein a predetermined number of said feedback inputs are also input to said second matrix mixing means.

3. An apparatus as claimed in claim 1 wherein said feedback response filtering comprises a reverberation filter.

4. An apparatus as claimed in claim 3 wherein said reverberation filter comprises one of a sparse tap FIR, a recursive algorithmic filter or a full convolution FIR filter.

5. An apparatus as claimed in claim 1 wherein said audio inputs comprise a surround sound set of signals.

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

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

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

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

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

11. An apparatus as claimed in claim 1 wherein said filter system includes a reverberation filter interconnected to the sum of said audio inputs.

12. An apparatus as claimed in claim 1, wherein said one or more filters to account for the direct response also account for the short time echo response of the room.