Surround sound panner

Details Surround sound panner Surround sound panner

2000-01-27

2003-01-14

Isen, Forester W. (Department: 2644)

Electrical audio signal processing systems and devices

Binaural and stereophonic

Pseudo stereophonic

C381S018000, C381S063000

Reexamination Certificate

active

06507658

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to audio signal processing, and more specifically, to a method and apparatus for surround sound panning.
2. Description of the Related Art
Surround sound audio (wherein, for example, sound is generated for one or more listeners
105
,
106
using multiple speakers i 100-104, each respectively positioned at angle &phgr;(i) from listener
105
(positioned at a “sweet spot”), as illustrated in
FIG. 1
) is growing rapidly due to the proliferation of home theaters, digital television, surround sound music, and computer games. The roots of surround sound audio are in the motion picture industry. It has been employed by movie soundtracks to locate sounds, creating a captivating environment for the theater patron. Typical theaters have three speakers in the front which provide stereo along with a center channel for dialog, and two speakers in the rear for special effects and ambient sounds. In recent years this technology has made its way to the home, fueling a rapidly growing surround sound home theater market. Dolby ProLogic has been used to enhance television shows by creating a surround sound effect. Technologies such as DVD are bringing advanced multi-channel digital audio into the home, providing an audio experience rivaling or exceeding that found in movie theaters.
In addition to DVD, surround sound is being integrated into personal computers and many new consumer media delivery systems. Among these are High Definition Television and the new digital television standard. This new technology will replace the older Dolby ProLogic surround technology. Soon all TV shows, sporting events, and commercials will be broadcast in surround sound. In addition, surround sound is currently available on most videotapes and laserdiscs.
Another area in which surround sound is emerging is recorded music. Currently, Digital Theater Systems (DTS) markets a CD-based technology that provides a high-quality six-channel audio technology for the home. Currently, industry standards committees are in the final stages of defining an audio-only DVD format. Initial music industry response to this technology has been extremely favorable.
Following is a list of current listening formats for surround sound:
5.1: Six-channel format popular in home theaters and movie theaters having left, center, and right speakers positioned in front of the listener, and left and right surround speakers behind the listener (see FIG.
2
A).
7.1: Motion picture format having five full-range screen channels, two surround channels and one LFE channel. Also a consumer format with additional side or front channels (see FIG.
2
B).
LCRS: Four-channel format having a single rear surround channel, often sent simultaneously to left and right surround speakers placed behind the listener (see FIG.
2
C). Following is a list of current encoding formats for surround sound:
Discrete Multichannel: A system wherein audio channels are separately recorded, stored and played back.
Dolby Digital (AC-3): A digital encoding format for up to 5.1-channel audio using lossy data compression. Used in motion picture theatres and consumer audio and video equipment. Standard for DTV (digital television); used on most DVDs and many laserdiscs.
DTS: Refers to digital encoding formats from Digital Theater Systems. Used in motion picture theaters for up to eight (usually 5.1) channels, for discrete 5.1-channel music on CDs, and optional for video soundtracks on DVDs and laserdiscs.
Sony Dynamic Digital Sound (SDDS): A 7.1-channel format used in motion picture theaters.
Dolby Surround: A format used to encode LCRS audio for two-channel media, used in some television broadcasts, analog optical motion picture soundtracks, and VHS tapes; decoded using Dolby ProLogic.
Meridian Lossless Packing (MLP): A lossless data compression technique planned for use on the upcoming DVD-audio format.
One of the important aspects of creating surround sound is panning. That is, when creating surround sound, a source sound signal is “panned”to each of the separate discrete channels so as to add spatial characteristics such as direction to the sound. Low-frequency effects are mixed to a separate so-called LFE channel. The LFE channel carries non-essential effects enhancement, such as the low-frequency component of an explosion.
When surround sound was initially introduced, all dialog was mapped to the center channel, stereo was mapped to left and right channels, and ambient sounds were mapped to the surround (rear) channels. Recently, however, all channels are used to locate certain sounds via panning, which is particularly useful for sound sources such as explosions or moving vehicles.
The concept of panning will now be introduced with reference to
FIGS. 3
,
4
A, and
4
B. First,
FIG. 3
illustrates the head-related transfer function (hrtf) h(t,&phgr;), consisting of right ear and left ear components h
L
(t,&phgr;) (
304
) and h
R
(t,&phgr;) (
305
). Specifically, a source sound c(t) originating from speaker
300
, located at an arrival angle &phgr; from listener
301
will cause the listener to hear a sound in the left and right ears as signals l(t) (
307
) and r(t) (
308
) respectively, and in turn perceive the sound to be arriving from direction &phgr;. The left and right listener ear signals l(t) and r(t) thus can be determined as:
 
l
(
t
)=
h
L
(
t,&phgr;
)*
c
(
t
)  (Eq. 1)
r
(
t
)=
h
R
(
t,&phgr;
)*
c
(
t
)  (Eq. 2)
(where * represents a convolution operator)
FIG.
4
A and
FIG. 4B
introduce the concept of panning with respect to stereo signals. As shown in
FIG. 4A
, a signal s(t) is applied to left and right speakers
409
and
411
, respectively, via amplifiers
405
and
406
. The left and right speakers are positioned from listener's
416
left ear by arrival angle &phgr;
1
, and right ear by arrival angle &phgr;
r
. Amplifiers
405
and
406
respectively provide a gain determined by panning weights &ggr;
1
(&agr;) (
403
) and &ggr;
r
(&agr;) (
404
) (where &agr; is between 0 and 1).
FIG. 4B
illustrates how a panning law is applied to determine how weights are applied to different speakers. As shown in
FIG. 4B
, a panning parameter &agr; (representing, for example, a “fade”value between the left and right channels) is input to the panning law
417
to produce respective panning weights &ggr;
1
(&agr;) and &ggr;
r
(&agr;), shown as array
418
. An application of one example of a panning law is where:
&ggr;
l
(&agr;)=&agr;  (Eq.3)
&ggr;
r
(&agr;)=1−&agr;(Eq.4)
When such a panning law is applied to the arrangement shown in
FIG. 4A
, the stereo speaker-to-ear impulse response (for each ear) of a panned source
410
, h
p
(t), can be described as:
h
p
(
t
)=&ggr;
1
h
(
t,&phgr;
1
)+&ggr;
r
h
(
t,&phgr;
r
)  (Eq.5)
h
p
(
t
)=&agr;
h
(
t,&phgr;
l
)+(1−&agr;)
h
(
t,&phgr;
r
)  (Eq.6)
It turns out that the speaker-to-ear impulse response of an actual sound source at direction &phgr;
a
(where &phgr;
a
=&agr;×&phgr;
l
+(1−&agr;)×&phgr;
r
), approximates the panned impulse response for closely spaced speakers, that is
h
p
(
t
)≈
h
(
t,&phgr;
a
)  (Eq.7)
and, as a result, panning between speakers has the perceptual effect of a single speaker positioned at &phgr;
a.
FIGS. 5A and 5B
further illustrate how the above panning concepts are applied to surround sound systems. As shown in
FIG. 5A
, a source sound signal s(t) is applied to a set of speakers i=
1
to N via respective amplifiers
501
. . .
503
. Each amplifier i applies a gain determined by respective panning weights &ggr;
i
(&eegr;) so as to produce separate channel signals c
i
(t), where c
i
(t) is defined as:
c
i
(
t
)=&ggr;
i
(&eegr;)
s
(
t
)  (Eq.8)
As shown in
FIG. 5B
, each respective panning weight &ggr;
i
(&eegr;) (
512
) is determined by panning law
511
, which yields each panning weight as a function of panning parameters &eeg

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