Bomb-H POWER
US005912976A
Ulllted States Patent [19]
[11] Patent Number:
Klayman et al.
[45]
[54]
MULTI-CHANNEL AUDIO ENHANCEMENT
SYSTEM FOR USE IN RECORDING AND
PLAYBACK AND METHODS FOR
PROVIDING SAME
5,912,976
Date of Patent:
Jun. 15, 1999
OTHER PUBLICATIONS
Schroeder, M.R., “An Arti?cial Stereophonic Effect
Obtained from a Single Audio Signal”,Journal of theAua'io
Engineering Society, vol. 6, No. 2, pp. 74—79, Apr. 1958.
KuroZumi, K., et al., “A NeW Sound Image Broadening
Control System Using a Correlation Coef?cient Variation
[75] Inventors? Arnold I- Klaymalb Humingmn Beach;
Alan D- Kraemel‘, Tllstln, both of
Cahf
Method”, Electronics and Communications in Japan, vol.
_
_
_
67—A, No. 3, pp. 204—211, Mar. 1984.
[73] Asslgnee' SRS Labs’ Inc" Irvlne’ Cahf'
Sundberg, J., “The Acoustics of the Singing Voice”, The
[21]
Physics of Music, pp. 16—23, 1978.
A 1 N ' 08/743 776
pp '
[22]
5
O"
Filed;
I C] 6
’
Ishihara, M., “A NeW Analog Signal Processor For A Stereo
Nov, 7, 1996
00
Enhancement System”, IEEE Transactions on Consumer
Electronics, vol. 37, No. 4, pp. 806—813, Nov. 1991.
%5g
Ci ................................................... 3.81/18 331/1
Allison, R.’ “The Loudspeaker / Living Room System”,
[58]
Field
- - of- Search
.................................................
.................................. .. 381/1, 17, 18,
H04R
Audio)
381/19, 20, 22, 23, 307, 300, 27
18_22,
“
PIOV~
.
.
,,
.
_
Vaughan, D., HoW We Hear Direction ,Aua'io, pp. 51 55,
Dec. 1983.
[56]
References Cited
(List continued on next page.)
U ' S ' PATENT DOCUMENTS
3,170,991
3,229,038
P rimar
.
y Examiner—l\/l1nsun
.
.
Oh H arve y
2/1965 Glasgal .
1/1966 Richter.
Attorney, Agent, or Firm—Knobbe, Martens, Olson & Bear
LLP
(List continued on neXt page.)
[57]
FOREIGN PATENT DOCUMENTS
0
0
0
O
097
320
367
354
982 A3 1/1984
270A2 6/1989
569 A2 10/1989
517 A2 2/1990
O 357 402 A2
3/1990
35 014 2
/1966
33 31 352 A1 3/1985
4029936 10/1940
43.12585 5/1943
58-144989 9/1983
59-27692 2/1984
61-33600 2/1986
61466696 10/1986
European
European
European
European
Pat~
PatPat'
Pat‘
OffOff
O?Off‘
ABSTRACT
An audio enhancement system and method for use receives
a group of multi-channel audio signals and provides a
simulated surround sound environment through playback of
only tWo output signals. The multi-channel audio signals
comprise a pair of front signals intended for playback from
a forWard sound stage and a pair of rear signals intended for
'
European Pat. Off. .
-
.
Germany '
Japan _
Japan _
playback from a rear sound stage. The front and rear signals
d.? d.
. b
.
b.
f
are mo .1 e in pairs y separating an am 1ent component 0
each pair of signals from a direct component and processing
at least some of the components With a head-related transfer
Japan
Japan
Japan
Japan
function. Processing of the individual audio signal compo
nents is determined by an intended playback position of the
corresponding original audio signals. The individual audio
signal components are then selectively combined With the
Finland.
.
.
- _
g
g?ggg? '
W0 87/O6O9O 10/1987
WIPO _
WO 94/16548
7/1994
WIPO .
WO 96/34509 10/1996
WIPO .
g
original audio signals to form tWo enhanced output signals
'
for generating a surround sound experience upon playback.
48 Claims, 10 Drawing Sheets
i
1
MU —CHANNEL Aumo
GNAL SOU RCE
MULTl-CHANNEL
MlXED OUTPUTS
\MMERSION PROCESSOR
BF cP Lp
41k 42 26y
Bomb-H
za’ RP
POWER
AMPUFlER
- RECORDlNG
DEVlCE
5,912,976
Page 2
US. PATENT DOCUMENTS
3,246,081
3,249,696
3,665,105
3,697,692
3,725,586
3,745,254
3,757,047
3,761,631
3,772,479
3,849,600
3,885,101
3,892,624
3,925,615
3,943,293
4,024,344
4,063,034
4,069,394
4,118,599
4,139,728
4,192,969
4,204,092
4,209,665
4,218,583
4,218,585
4,219,696
4,237,343
4,239,937
4,303,800
4,308,423
4,308,424
4,309,570
4,332,979
4,349,698
4,355,203
4,356,349
4,393,270
4,394,536
4,408,095
4,479,235
4,489,432
4,495,637
4,497,064
4,503,554
4,567,607
4,569,074
4/1966
5/1966
5/1972
10/1972
4/1973
7/1973
9/1973
9/1973
11/1973
11/1974
5/1975
7/1975
12/1975
3/1976
5/1977
12/1977
1/1978
10/1978
2/1979
3/1980
5/1980
6/1980
8/1980
8/1980
8/1980
12/1980
12/1980
12/1981
12/1981
12/1981
1/1982
6/1982
9/1982
10/1982
10/1982
7/1983
7/1983
10/1983
10/1984
12/1984
1/1985
1/1985
3/1985
1/1986
2/1986
Edwards .
Van Sickle .
Chowning .
Ha?er .
Iida .
Ohta et al. .
Ito et al. .
Ito et al. .
Hilbert .
Ohshima .
Ito et al. .
Shimada .
Nakano .
Bailey .
Dolby et al. .
Peters .
Doi et al. .
Iwahara et al. .
Haramoto et al. .
Iwahara .
Bruney .
Iwahara .
Poulo .
Carver .
Kogure et al. .
Kurtin et al. .
Kampmann .
DeFreitas .
Cohen .
Bice, Jr. .
4,589,129
4,594,610
4,594,729
4,594,730
4,622,691
4,648,117
4,696,036
4,703,502
4,748,669
4,856,064
4,866,774
4,866,776
4,888,809
4,933,768
4,953,213
5,033,092
5,046,097
5,105,462
5,146,507
5,208,860
5,228,085
5,251,260
5,319,713
5,325,435
5,371,799
5,400,405
5,572,591
5,677,957
5,734,724
5,742,688
5,771,295
5,799,094
5/1986
6/1986
6/1986
6/1986
11/1986
3/1987
9/1987
10/1987
5/1988
8/1989
9/1989
9/1989
12/1989
6/1990
8/1990
7/1991
9/1991
4/1992
9/1992
5/1993
7/1993
10/1993
6/1994
6/1994
12/1994
3/1995
11/1996
10/1997
3/1998
4/1998
6/1998
8/1998
Blackmer et al. .
Patel .
Weingartner .
Rosen .
Tokumo et al. .
Kunugi et al. .
Julstrom .
Kasai et al. .
Klayman .
Iwamatsu .
Klayman .
Kasai et al. .
Knibbeler .
Ishikawa
................................... .. 381/1
Tasaki et al. .
Sadaie .
Lowe et al. .
Lowe et al. .
Satoh et al. .
Lowe et al. .
Aylward .
Gates .
Waller, Jr. et al. .
Date et al. .
Lowe et al. .
Petroff .
NumaZu
.................................... .. 381/1
Hulsebus ..
Kinoshita .
381/17
381/17
Ogawa .
381/17
Waller ..
381/18
Mouri ...................................... .. 381/18
Carver .
Fischer .
OTHER PUBLICATIONS
Iwahara .
Cohen .
Robinson .
Stevens, S., et al, “Chapter 5: The Two—Earned Man”, Sound
And Hearing, pp. 98—106 and 196, 1965.
Van Den Berg .
Eargle, J ., “Multichannel Stereo Matrix Systems: An Over
Shima et al. .
view”, Journal of the Audio Engineering Society, pp.
Ariga et al. .
552—558 (no date listed).
Gri?is .
Wilson, Kim, “AC—3 Is Here! But Are You Ready To Pay
The Price?”, Home Theater; pp. 60—65, Jun. 1995.
Copy of International Search Report dated Mar. 10, 1998
Polk .
Bruney .
Polk .
Bruney et al. .
from corresponding PCT application.
Kaufman, Richard 1., “Frequency Contouring For Image
Polk .
Enhancement”, Audio, pp. 34—39, Feb. 1985.
Davis .
U.S. Patent
Jun. 15,1999
Sheet 1 0f 10
5,912,976
'
10
,5
/
MULTI—CHANNEL AuDIO
SIGNAL SOURCE
A0A1A2A3A4A5A5A7
B c
,6,
20
K
SIGNAL MIXER
B
c
22
I
24
\
MULTl-CHANNEL
MIXED OUTPUTS
V
MULTl-CHANNEL AUDIO
IMMERSION PROCESSOR
BP
40
CP
4;
LP
RP
2i
\
II
B OUT O_d4___
COUTO—<—————
46‘
28
r30
' RECORDING
‘
;
_
A
,
DEVICE
I
/32
POWER
AMPLIFIER
LOIJT %
% ROuT
K35
U.S. Patent
Jun. 15,1999
Sheet 2 0f 10
5,912,976
FIG. 2
,/50
[.90
52
r ——————————— ~—*—————I
Q
54|
56‘
|
OASIS‘? é?
SOURCE(S)
I
MULTl-CHANNEL
\
|
l
I
I
I
DIGITAL AUDIO DECODER
B
I
C
II
I
l
l
|
I
55
II
/50 I
I
I
AUDIO IMMERSION
I
'
PROCESSOR
I
I
l
l
,_
I
l____ ____ff2____ _€4___l
BP cP
I
LP
RP
I DIGITAL/ANALOG
I
I
CONVERTER
fja
BP
CP
LP “72 74
55
70
\
8
I
4\
J
I
A
II
I
POWER
}
AMPLIFIER
CouT
Low"
‘
' RECORDING
I
BOUT
86,
50\
RP
80
82 1 ROUT
I
32
/
DEVICE
U.S. Patent
Jun. 15, 1999
\\
6Em
Sheet 4 0f 10
5,912,976
U.S. Patent
Jun. 15,1999
Sheet 7 0f 10
501Al
PD‘IOJ
Cm: m xi
5,912,976
Ami;
+
w >wvl
PIQE 5x5
U.S. Patent
Jun. 15,1999
Sheet 8 0f 10
5,912,976
F/G.9
_
_
_
_
_
_
_
_
_
_
_
_ .
~
_
_
_
i
_
_
_
_
_
_
_
_
i
2O
1 0O
1 0k
FREQ(Hz)
i
i
i
i
_
_
_
20k
U S Patent
Jun. 15,1999
Sheet 9 0f 10
5,912,976
F/ G . I0
352
1 OO
1 0k
20k
U.S. Patent
Jun. 15,1999
Sheet 10 0f 10
5,912,976
gam a
QN
5,912,976
1
2
MULTI-CHANNEL AUDIO ENHANCEMENT
SYSTEM FOR USE IN RECORDING AND
PLAYBACK AND METHODS FOR
PROVIDING SAME
duced on rear left and right speakers, one channel is used for
a forWard center dialogue speaker, and one channel is used
for loW-frequency and effects signals. Audio playback sys
tems Which can accommodate the reproduction of all these
six channels do not require that the signals be mixed into a
FIELD OF THE INVENTION
tWo channel format. HoWever, many playback systems,
including today’s typical personal computer and tomorroW’s
This invention relates generally to audio enhancement
systems and methods for improving the realism and dra
matic effects obtainable from tWo channel sound reproduc
tion. More particularly, this invention relates to apparatus
personal computer/television, may have only tWo channel
playback capability (excluding center and subWoofer
channels). Accordingly, the information present in addi
tional audio signals, apart from that of the conventional
and methods for enhancing multiple audio signals and
stereo signals, like those found in an AC-3 recording, must
mixing these audio signals into a tWo channel format for
either be electronically discarded or mixed into a tWo
reproduction in a conventional playback system.
BACKGROUND OF THE INVENTION
15
Audio recording and playback systems can be character
mixing method may be to simply combine all of the signals
into a tWo-channel format While adjusting only the relative
iZed by the number of individual channel or tracks used to
input and/or play back a group of sounds. In a basic stereo
recording system, tWo channels each connected to a micro
phone may be used to record sounds detected from the
gains of the mixed signals. Other techniques may apply
frequency shaping, amplitude adjustments, time delays or
phase shifts, or some combination of all of these, to an
distinct microphone locations. Upon playback, the sounds
recording by the tWo channels are typically reproduced
through a pair of loudspeakers, With one loudspeaker repro
ducing an individual channel. Providing tWo separate audio
channels for recording permits individual processing of
channel format.
There are various techniques and methods for mixing
multi-channel signals into a tWo channel format. A simple
individual audio signal during the ?nal mixing process. The
particular technique or techniques used may depend on the
25
these channels to achieve an intended effect upon playback.
format and content of the individual audio signals as Well as
the intended use of the ?nal tWo channel mix.
For example, US. Pat. No. 4,393,270 issued to van den
Berg discloses a method of processing electrical signals by
modulating each individual signal corresponding to a pre
selected direction of perception Which may compensate for
placement of a loudspeaker. A separate multi-channel pro
cessing system is disclosed in US. Pat. No. 5,438,623 issued
to Begault. In Begault, individual audio signals are divided
into tWo signals Which are each delayed and ?ltered accord
ing to a head related transfer function (HRTF) for the left
Similarly, providing more discrete audio channels alloWs
more freedom in isolating certain sounds to enable the
separate processing of these sounds.
Professional audio studios use multiple channel record
ings systems Which can isolate and process numerous indi
vidual sounds. HoWever, since many conventional audio
reproduction devices are delivered in traditional stereo, use
of a multi-channel system to record sounds requires that the 35
and right ears. The resultant signals are then combined to
sounds be “mixed” doWn to only tWo individual signals. In
generate left and right output signals intended for playback
the professional audio recording World, studios employ such
through a set of headphones.
mixing methods since individual instruments and vocals of
a given audio Work may be initially recorded on separate
tracks, but must be replayed in a stereo format found in
The techniques found in the prior art, including those
found in the professional recording arena, do not provide an
effective method for mixing multi-channel signals into a tWo
conventional stereo systems. Professional systems may use
48 or more separate audio channels Which are processed
individually before recorded onto tWo stereo tracks.
In multi-channel playback systems, i.e., de?ned herein as
systems having more than tWo individual audio channels,
45
each sound recorded from an individual channel may be
separately processed and played through a corresponding
speaker or speakers. Thus, sounds Which are recorded from,
or intended to be placed at, multiple locations about a
listener, can be realistically reproduced through a dedicated
speaker placed at the appropriate location. Such systems
have found particular use in theaters and other audio-visual
environments Where a captive and ?xed audience experi
ences both an audio and visual presentation. These systems,
Which include Dolby Laboratories’ “Dolby Digital” system;
the Digital Theater System (DTS); and Sony’s Dynamic
55
channel format to achieve a realistic audio reproduction
through a limited number of discrete channels. As a result,
much of the ambiance information Which provides an
immersive sense of sound perception may be lost or masked
in the ?nal mixed recording. Despite numerous previous
methods of processing multi-channel audio signals to
achieve a realistic experience through conventional tWo
channel playback, there is much room for improvement to
achieve the goal of a realistic listening experience.
Accordingly, it is an object of the present invention to
provide an improved method of mixing multi-channel audio
signals Which can be used in all aspects of recording and
playback to provide an improved and realistic listening
experience. It is an object of the present invention to provide
an improved system and method for mastering professional
audio recordings intended for playback on a conventional
stereo system. It is also an object of the present invention to
provide a system and method to process multi-channel audio
Digital Sound (SDDS), are all designed to initially record
and then reproduce multi-channel sounds to provide a sur
round listening experience.
In the personal computer and home theater arena,
recorded media is being standardiZed so that multiple
signals extracted from an audio-visual recording to provide
channels, in addition to the tWo conventional stereo
channels, are stored on such recorded media. One such
a limited number of audio channels.
standard is Dolby’s AC-3 multi-channel encoding standard
Which provides six separate audio signals. In the Dolby
AC-3 system, tWo audio channels are intended for playback
on forWard left and right speakers, tWo channels are repro
an immersive listening experience When reproduced through
For example, personal computers and video players are
emerging With the capability to record and reproduce digital
65
video disks (DVD) having six or more discrete audio
channels. HoWever, since many such computers and video
players do not have more than tWo audio playback channels
5,912,976
3
4
(and possibly one sub-Woofer channel), they cannot use the
full amount of discrete audio channels as intended in a
surround environment. Thus, there is a need in the art for a
FIG. 5 is a perspective vieW of a personal computer
having an audio enhancement system constructed in accor
dance With the present invention for creating a surround
computer and other video delivery system Which can effec
tively use all of the audio information available in such
sound effect from tWo output signals.
FIG. 6 is a schematic block diagram of the personal
systems and provide a tWo channel listening experience
Which rivals multi-channel playback systems. The present
thereof.
computer of FIG. 5 depicting major internal components
invention ful?lls this need.
SUMMARY OF THE INVENTION
10
An audio enhancement system and method is disclosed
for processing a group of audio signals, representing sounds
FIG. 8 is a schematic block diagram of a preferred
embodiment for processing and mixing a group of AC-3
audio signals to achieve a surround-sound experience from
existing in a 360 degree sound ?eld, and combining the
group of audio signals to create a pair of signals Which can
accurately represent the 360 degree sound ?eld When played
through a pair of speakers. The audio enhancement system
FIG. 7 is a diagram depicting the perceived and actual
origins of sounds heard by a listener during operation of the
personal computer shoWn in FIG. 5.
15
a pair of output signals.
FIG. 9 is a graphical representation of a ?rst signal
equalization curve for use in a preferred embodiment for
can be used as a professional recording system or in personal
computers and other home audio systems Which include a
processing and mixing a group of AC-3 audio signals to
achieve a surround-sound experience from a pair of output
limited amount of audio reproduction channels.
signals.
In a preferred embodiment for use in a home audio
FIG. 10 is a graphical representation of a second signal
reproduction system having stereo playback capability, a
multi-channel recording provides multiple discrete audio
equalization curve for use in a preferred embodiment for
signals consisting of at least a pair of left and right signals,
processing and mixing a group of AC-3 audio signals to
achieve a surround-sound experience from a pair of output
a pair of surround signals, and a center channel signal. The
home audio system is con?gured With speakers for repro
25
signals.
ducing tWo channels from a forWard sound stage. The left
FIG. 11 is a schematic block diagram depicting the
and right signals and the surround signals are ?rst processed
and then mixed together to provide a pair of output signals
for playback through the speakers. In particular, the left and
right signals from the recording are processed collectively to
provide a pair of spatially-corrected left and right signals to
various ?lter and ampli?cation stages for creating the ?rst
signal equalization curve of FIG. 9.
FIG. 12 is a schematic block diagram depicting the
various ?lter and ampli?cation stages for creating the second
signal equalization curve of FIG. 10.
enhance sounds perceived by a listener as emanating from a
forward sound stage.
The surround signals are collectively processed by ?rst
isolating the ambient and monophonic components of the
surround signals. The ambient and monophonic components
DETAILED DESCRIPTION OF THE
PREFERRED EMBODIMENTS
35
FIG. 1 depicts a block diagram of a ?rst preferred
embodiment of a multi-channel audio enhancement system
10 for processing a group of audio signals and providing a
of the surround signals are modi?ed to achieve a desired
spatial effect and to separately correct for positioning of the
playback speakers. When the surround signals are played
through forWard speakers as part of the composite output
pair of output signals. The audio enhancement system 10
comprises a source of multi-channel audio signal source 16
Which outputs a group of discrete audio signals 18 to a
signals, the listener perceives the surround sounds as ema
nating from across the entire rear sound stage. Finally, the
multi-channel signal mixer 20. The mixer 20 provides a set
of processed multi-channel outputs 22 to an audio immer
sion processor 24. The signal processor 24 provides a
center signal may also be processed and mixed With the left,
right and surround signals, or may be directed to a center
channel speaker of the home reproduction system if one is
45
channel signal 28 Which can be directed to a recording
device 30 or to a poWer ampli?er 32 before reproduction by
present.
a pair of speakers 34 and 36. Depending upon the signal
inputs 18 received by the processor 20, the signal mixer may
also generate a bass audio signal 40 containing loW
frequency information Which corresponds to a bass signal,
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other aspects, features, and advantages of
the present invention Will be more apparent from the fol
loWing particular description thereof presented in conjunc
B, from the signal source 16, and/or a center audio signal 42
containing dialogue or other centrally located sounds Which
corresponds to a center signal, C, output from the signal
tion With the folloWing draWings, Wherein:
FIG. 1 is a schematic block diagram of a ?rst embodiment
of a multi-channel audio enhancement system for generating
a pair of enhanced output signals to create a surround-sound
effect.
processed left channel signal 26 and a processed right
55
source 16. Not all signal sources Will provide a separate bass
effects channel B, nor a center channel C, and therefore it is
to be understood that these channels are shoWn as optional
FIG. 2 is a schematic block diagram of a second embodi
ment of a multi-channel audio enhancement system for
signal channels. After ampli?cation by the ampli?er 32, the
generating a pair of enhanced output signals to create a
surround-sound effect.
FIG. 3 is a schematic block diagram depicting an audio
and 46, respectively.
audio signals.
tral or other audio performance. Alternatively, the audio
signals 40 and 42 are represented by the output signals 44
In operation, the audio enhancement system 10 of FIG. 1
receives audio information from the audio source 16. The
enhancement process for enhancing selected pairs of audio
audio information may be in the form of discrete analog or
signals.
digital channels or as a digital data bitstream. For example,
FIG. 4 is a schematic block diagram of an enhancement 65 the audio source 16 may be signals generated from a group
of microphones attached to various instruments in an orches
circuit for processing selected components from a pair of
5,912,976
5
6
source 16 may be a pre-recorded multi-track rendition of an
mere personal preference. For eXample, the processing per
formed Within the region 90 may be accomplished Wholly
Within a digital signal processor (DSP), Within softWare
audio Work. In any event, the particular form of audio data
received from the source 16 is not particularly relevant to the
loaded into a computer’s memory, or as part of a micro
operation of the enhancement system 10.
processor’s native signal processing capabilities such as that
found in Intel’s Pentium generation of micro-processors.
For illustrative purposes, FIG. 1 depicts the source audio
signals as comprising eight main channels AO—A7, a single
bass or loW-frequency channel, B, and a single center
channel signal, C. It can be appreciated by one of ordinary
skill in the art that the concepts of the present invention are
equally applicable to any multi-channel system of greater or
feWer individual audio channels.
As Will be explained in more detail in connection With
FIGS. 3 and 4, the multi-channel immersion processor 24
modi?es the output signals 22 received from the miXer 20 to
10
Referring noW to FIG. 3, the immersion processor 24
from FIG. 1 is shoWn in association With the signal miXer 20.
The processor 24 comprises individual enhancement mod
ules 100, 102, and 104 Which each receives a pair of audio
signals from the miXer 20. The enhancement modules 100,
102, and 104 process a corresponding pair of signals on the
output signals, L0,” and Rom, are acoustically reproduced.
stereo level in part by isolating ambient and monophonic
components from each pair of signals. These components,
along With the original signals are modi?ed to generate
resultant signals 108, 110, and 112. Bass, center and other
signals Which undergo individual processing are delivered
The processor 24 is shoWn in FIG. 1 as an analog processor
along a path 118 to a module 116 Which may provide level
operating in real time on the multi-channel miXed output
signals 22. If the processor 24 is an analog device and if the
audio source 16 provides a digital data output, then the
adjustment, simple ?ltering, or other modi?cation of the
received signals 118. The resultant signals 120 from the
module 116, along With the signals 108, 110, and 112 are
create an immersive three-dimensional effect When a pair of 15
output to a miXer 124 Within the processor 24.
processor 24 must of course include a digital-to-analog
In FIG. 4, an eXemplary internal con?guration of a
converter (not shoWn) before processing the signals 22.
Referring noW to FIG. 2, a second preferred embodiment
of a multi-channel audio enhancement system is shoWn
Which provides digital immersion processing of an audio
preferred embodiment for the module 100 is depicted. The
module 100 consists of inputs 130 and 132 for receiving a
25
source. An audio enhancement system 50 is shoWn com
prising a digital audio source 52 Which delivers audio
information along a path 54 to a multi-channel digital audio
decoder 56. The decoder 56 transmits multiple audio chan
pair of audio signals. The audio signals are transferred to a
circuit or other processing means 134 for separating the
ambient components from the direct ?eld, or monophonic,
sound components found in the input signals. In a preferred
embodiment, the circuit 134 generates a direct sound com
nel signals along a path 58. In addition, optional bass and
center signals B and C may be generated by the decoder 56.
ponent along a signal path 136 representing the summation
signal M1+M2. A difference signal containing the ambient
components of the input signals, MIL-M2, is transferred
Digital data signals 58, B, and C, are transmitted to an audio
immersion processor 60 operating digitally to enhance the
received signals. The processor 60 generates a pair of
enhanced digital signals 62 and 64 Which are fed to a digital
to analog converter 66. In addition, the signals B and C are
fed to the converter 66. The resultant enhanced analog
along a path 138. The sum signal M1+M2 is modi?ed by a
circuit 140 having a transfer function F1. Similarly, the
difference signal MIL-M2 is modi?ed by a circuit 142 having
a transfer function F2. The transfer functions F1 and F2 may
be identical and in a preferred embodiment provide spatial
35
enhancement to the inputted signals by emphasiZing certain
frequencies While deemphasiZing others. The transfer func
tions F1 and F2 may also apply HRTF-based processing to
the inputted signals in order to achieve a perceived place
ment of the signals upon playback. If desired, the circuits
signals 68 and 70, corresponding to the loW frequency and
center information, are fed to the poWer ampli?er 32.
Similarly, the enhanced analog left and right signals, 72, 74,
are delivered to the ampli?er 32. The left and right enhanced
signals 72 and 74 may be diverted to a recording device 30
for storing the processed signals 72 and 74 directly on a
recording medium such as magnetic tape or an optical disk.
Once stored on recorded media, the processed audio infor
mation corresponding to signals 72 and 74 may be repro
duced by a conventional stereo system Without further
enhancement processing to achieve the intended immersive
effect described herein.
140 and 142 may be used to insert time delays or phase shifts
of the input signals 136 and 138 With respect to the original
signals M1 and M2.
The circuits 140 and 142 output a respective modi?ed
sum and difference signal, (M1+M2)P and (M1—M2)P, along
paths 144 and 146, respectively. The original input signals
M1 and M2, as Well as the processed signals (M1+M2)P and
(M 1—M2)P are fed to multipliers Which adjust the gain of the
The ampli?er 32 delivers an ampli?ed left output signal
80, LOUT, to the left speaker 34 and delivers an ampli?ed
received signals. After processing, the modi?ed signals eXit
the enhancement module 100 at outputs 150, 152, 154, and
156. The output 150 delivers the signal KlMl, the output
152 delivers the signal K2F1(M1+M2), the output 154 deliv
right output signal 82, ROUT, to the right speaker 36. Also,
an ampli?ed bass effects signal 84, BOUT, is delivered to a
sub-Woofer 86. An ampli?ed center signal 88, COUT, may be
delivered to an optional center speaker (not shoWn). For near
?eld reproductions of the signals 80 and 82, i.e., Where a
listener is position close to and in betWeen the speakers 34
55
ers the signal K3F4(M1—M2), and the output 156 delivers the
signal K4M2, Where K1—K4 are constants determined by the
setting of multipliers 148. The type of processing performed
by the modules 100, 102, 104, and 116, and in particular the
and 36, use of a center speaker may not be necessary to
circuits 134, 140, and 142 may be user-adjustable to achieve
achieve adequate localiZation of a center image. HoWever, in
far-?eld applications Where listeners are positioned rela
tively far from the speakers 34 and 36, a center speaker can
be used to ?X a center image betWeen the speaker 34 and 36.
The combination consisting largely of the decoder 56 and
the processor 60 is represented by the dashed line 90 Which
may be implemented in any number of different Ways
depending on a particular application, design constraints, or
a desired effect and/or a desired position of a reproduced
sound. In some cases, it may be desirable to process only an
ambient component or a monophonic component of a pair of
input signals. The processing performed by each module
may be distinct or it may be identical to one or more other
65
modules.
In accordance With a preferred embodiment Where a pair
of audio signals is collectively enhanced before mixing,
5,912,976
7
8
each module 100, 102, and 104 Will generate four processed
signals for receipt by the mixer 24 shown in FIG. 3. All of
the signals 108, 110, 112, and 120 may be selectively
combined by the mixer 124 in accordance With principles
system disclosed herein Will be described for use With Dolby
AC-3 recorded media. It can be appreciated, hoWever, that
the same or similar principles may be applied to other
common to one of ordinary skill in the art and dependent
upon a user’s preferences.
channels to create a surround sound experience. Moreover,
While a computer system 200 is shoWn and described in FIG.
By processing multi-channel signals at the stereo level,
i.e., in pairs, subtle differences and similarities Within the
paired signals can be adjusted to achieve an immersive effect
AC-3 recorded media may be a television, a combination
created upon playback through speakers. This immersive
effect can be positioned by applying HRTF-based transfer
standardiZed audio recording techniques Which use multiple
5, the audio-visual playback device for reproducing the
television/personal computer, a digital video disk player
10
functions to the processed signals to create a fully immersive
positional sound ?eld. Each pair of audio signals is sepa
rately processed to create a multi-channel audio mixing
system that can effectively recreate the perception of a live
15
360 degree sound stage. Through separate HRTF processing
(CPU) 220, a mass storage memory and a temporary random
of the components of a pair of audio signals, e.g., the
ambient and monophonic components, more signal condi
tioning control is provided resulting in a more realistic
immersive sound experience When the processed signals are
access memory (RAM) system 222, an input/output control
acoustically reproduced. Examples of HRTF transfer func
tions Which can be used to achieve a certain perceived
aZimuth are described in the article by E. A. B. ShaW entitled
“Transformation of Sound Pressure Level From the Free
Field to the Eardrum in the Horizontal Plane”,
coupled to a television, or any other device capable of
playing a multi-channel audio recording.
FIG. 6 is a schematic block diagram of the major internal
components of the processing unit 202 of FIG. 5. The unit
202 contains the components of a typical personal computer
system, constructed in accordance With principles common
to one of ordinary skill, including a central processing unit
25
J.Acoust.Soc.Am., Vol. 56, No. 6, December 1974, and in
the article by S. Mehrgarat and V. Mellert entitled “Trans
device 224, all interconnected via an internal bus structure.
The unit 202 also contains a poWer supply 226 and a
recorded media player/recorder 228 Which may be a DVD
device or other multi-channel audio source. The DVD player
228 supplies video data to a video decoder 230 for display
on a monitor. Audio data from the DVD player 228 is
transferred to an audio decoder 232 Which supplies multiple
channel digital audio data from the player 228 to an immer
sion processor 250. The audio information from the decoder
232 contains a left front signal, a right front signal, a left
formation Characteristics of the External Human Ear”,
J.Acoust.Soc.Am., Vol. 61, No. 6, June 1977, both of Which
are incorporated herein by reference as though fully set
surround signal, a right surround signal, a center signal, and
forth.
Although principles of the present invention as described
enhances the audio information from the decoder 232 in a
manner suitable for playback With a conventional stereo
above in connection With FIGS. 1—4 are suitable for use in
playback system. Speci?cally, a left channel signal 252 and
professional recording studios to make high-quality
recordings, one particular application of the present inven
a loW-frequency signal, all of Which are transferred to the
immersion audio processor 250. The processor 250 digitally
a right channel signal 254 are provided as outputs from the
35
tion is in audio playback devices Which have the capability
to process but not reproduce multi-channel audio signals.
For example, today’s audio-visual recorded media are being
processor 250. A loW-frequency sub-Woofer signal 256 is
also provided for delivery of bass response in a stereo
playback system. The signals 252, 254, and 256 are ?rst
provided to a digital-to-analog converter 258, then to an
encoded With multiple audio channel signals for reproduc
ampli?er 260, and then output for connection to correspond
tion in a home theater surround processing system. Such
surround systems typically include forWard or front speakers
ing speakers.
Referring noW to FIG. 7, a schematic representation of
speaker locations of the system of FIG. 5 is shoWn from an
for reproducing left and right stereo signals, rear speakers
for reproducing left surround and right surround signals, a
overhead perspective. The listener 212 is positioned in front
of and betWeen the left front speaker 206 and the right front
center speaker for reproducing a center signal, and a sub
Woofer speaker for reproduction of a loW-frequency signal.
45
Recorded media Which can be played by such surround
systems may be encoded With multi-channel audio signals
erated from an AC-3 compatible recording in accordance
With a preferred embodiment, a simulated surround experi
ence is created for the listener 212. In particular, ordinary
through such techniques as Dolby’s proprietary AC-3 audio
encoding standard. Many of today’s playback devices are
playback of tWo channel signals through the speakers 206
not equipped With surround or center channel speakers. As
a consequence, the full capability of the multi-channel
recorded media may be left untapped leaving the user With
an inferior listening experience.
Referring noW to FIG. 5, a personal computer system 200
is shoWn having an immersive positional audio processor
constructed in accordance With the present invention. The
computer system 200 consists of a processing unit 202
coupled to a display monitor 204. A front left speaker 206
and front right speaker 208, along With an optional sub
speaker 208. Through processing of surround signals gen
and 208 Will create a perceived phantom center speaker 214
from Which monophonic components of left and right sig
nals Will appear to emanate. Thus, the left and right signals
from an AC-3 six channel recording Will produce the center
phantom speaker 214 When reproduced through the speakers
55
206 and 208. The left and right surround channels of the
AC-3 six channel recording are processed so that ambient
surround sounds are perceived as emanating from rear
phantom speakers 215 and 216 While monophonic surround
sounds appear to emanate from a rear phantom center
reproducing audio signals generated by the unit 202. A
speaker 218. Furthermore, both the left and right front
signals, and the left and right surround signals, are spatially
listener 212 operates the computer system 200 via a key
enhanced to provide an immersive sound experience to
board 214. The computer system 200 processes a multi
channel audio signal to provide the listener 212 With an
eliminate the actual speakers 206, 208 and the phantom
speakers 215, 216, and 218, as perceived point sources of
sound. Finally, the loW-frequency information is reproduced
by an optional sub-Woofer speaker 210 Which may be placed
Woofer speaker 210 are all connected to the unit 202 for
immersive 360 degree surround sound experience from just
the speakers 206, 208 and the speaker 210 if available. In
accordance With a preferred embodiment, the processing
65
at any location about the listener 212.
5,912,976
9
10
signals SL and SR are ?rst fed through ?xed-gain ampli?ers
FIG. 8 is a schematic representation of an immersive
processor and mixer for achieving a perceived immersive
330 and 334, respectively, before transmission to the mixers
surround effect shoWn in FIG. 7. The processor 250 corre
280 and 284. Finally, the loW-frequency effects channel, B,
sponds to that shoWn in FIG. 6 and receives six audio
channel signals consisting of a front main left signal ML, a
front main right signal MR, a left surround signal SL, a right
surround signal SR, a center channel signal C, and a loW
frequency effects signal B. The signals ML and MR are fed
to corresponding gain-adjusting multipliers 252 and 254
Which are controlled by a volume adjustment signal Mvolume.
is fed through an ampli?er 336 to create the output loW
frequency effects signal, BOUT. Optionally, the loW fre
quency channel, B, may be mixed as part of the output
signals, LOUT and ROUT, if no subWoofer is available.
The enhancement circuit 250 of FIG. 8 may be imple
mented in an analog discrete form, in a semiconductor
10 substrate, through softWare run on a main or dedicated
The gain of the center signal C may be adjusted by a ?rst
microprocessor, Within a digital signal processing (DSP)
multiplier 256, controlled by the signal Mvolume, and a
chip, i.e., ?rmWare, or in some other digital format. It is also
possible to use a hybrid circuit structure combing both
second multiplier 258 controlled by a center adjustment
signal Cvolume. Similarly, the surround signals SL and SR are
?rst fed to respective multipliers 260 and 262 Which are
15
analog and digital components since in many cases the
source signals Will be digital. Accordingly, an individual
ampli?er, an equalizer, or other components, may be real
iZed by softWare or ?rmWare. Moreover, the enhancement
controlled by a volume adjustment signal Svolume.
The main front left and right signals, ML and MR, are each
fed to summing junctions 264 and 266. The summing
junction 264 has an inverting input Which receives MR and
306 and 320, may employ a variety of audio enhancement
a non-inverting input Which receives ML Which combine to
produce ML— R along an output path 268. The signal
techniques. For example, the circuit devices 270, 306, and
320 may use time-delay techniques, phase-shift techniques,
ML— R is fed to an enhancement circuit 270 Which is
signal equaliZation, or a combination of all of these tech
niques to achieve a desired audio effect. The basic principles
characteriZed by a transfer function P1. A processed differ
ence signal, (ML— R)P, is delivered at an output of the
circuit 270 to a gain adjusting multiplier 272. The output of
circuit 270 of FIG. 8, as Well as the enhancement circuits
of such audio enhancement techniques are common to one
25
the multiplier 272 is fed directly to a left mixer 280 and to
an inverter 282. The inverted difference signal (MR—ML)P is
transmitted from the inverter 282 to a right mixer 284. A
circuit 250 uniquely conditions a set of AC-3 multi-channel
signals to provide a surround sound experience through
playback of the tWo output signals LOUT and ROUT.
Speci?cally, the signals ML and MR are processed collec
tively by isolating the ambient information present in these
signals. The ambient signal component represents the dif
ferences betWeen a pair of audio signals. An ambient signal
component derived from a pair of audio signals is therefore
summation signal ML+MR exits the junction 266 and is fed
to a gain adjusting multiplier 286. The output of the multi
plier 286 is fed to a summing junction Which adds the center
channel signal, C, With the signal ML+MR. The combined
signal, ML+MR+C, exits the junction 290 and is directed to
both the left mixer 280 and the right mixer 284. Finally, the
original signals ML and MR are ?rst fed through ?xed gain
adjustment circuits, i.e., ampli?ers, 290 and 292,
of ordinary skill in the art.
In a preferred embodiment, the immersion processor
35
respectively, before transmission to the mixers 280 and 284.
The surround left and right signals, SL and SR, exit the
multipliers 260 and 262, respectively, and are each fed to
summing junctions 300 and 302. The summing junction 300
often referred to as the “difference” signal component.
While the circuits 270, 306, and 320 are shoWn and
described as generating sum and difference signals, other
embodiments of audio enhancement circuits 270, 306, and
320 may not distinctly generate sum and difference signals
at all. This can be accomplished in any number of Ways
has an inverting input Which receives SR and a non-inverting
using ordinary circuit design principles. For example, the
input Which receives SL Which combine to produce SL—SR
along an output path 304. All of the summing junctions 264,
isolation of the difference signal information and its subse
266, 300, and 302 may be con?gured as either an inverting
ampli?er or a non-inverting ampli?er, depending on Whether
a sum or difference signal is generated. Both inverting and
simultaneously at the input stage of an ampli?er circuit. In
addition to processing of AC-3 audio signal sources, the
circuit 250 of FIG. 8 Will automatically process signal
sources having feWer discrete audio channels. For example,
quent equaliZation may be performed digitally, or performed
45
non-inverting ampli?ers may be constructed from ordinary
operational ampli?ers in accordance With principles com
if Dolby Pro-Logic signals are input by the processor 250,
i.e., Where SL=SR, only the enhancement circuit 320 Will
mon to one of ordinary skill in the art. The signal SL—SR is
fed to an enhancement circuit 306 Which is characteriZed by
operate to modify the rear channel signals since no ambient
component Will be generated at the junction 300. Similarly,
if only tWo-channel stereo signals, ML and MR, are present,
a transfer function P2. A processed difference signal, (SL
SR)P, is delivered at an output of the circuit 306 to a gain
adjusting multiplier 308. The output of the multiplier 308 is
then the processor 250 operates to create a spatially
fed directly to the left mixer 280 and to an inverter 310. The
enhanced listening experience from only tWo channels
through operation of the enhancement circuit 270.
inverted difference signal (SR—SL)P is transmitted from the
inverter 310 to the right mixer 284. A summation signal
55
In accordance With a preferred embodiment, the ambient
information of the front channel signals, Which can be
SL+SR exits the junction 302 and is fed to a separate
enhancement circuit 320 Which is characteriZed by a transfer
represented by the difference ML—MR, is equaliZed by the
function P3. A processed summation signal, (SL+SR)P, is
circuit 270 according to the frequency response curve 350 of
delivered at an output of the circuit 320 to a gain adjusting
multiplier 332. While reference is made to sum and differ
ence signals, it should be noted that use of actual sum and
correction, or “perspective”, curve. Such equaliZation of the
ambient signal information broadens and blends a perceived
difference signals is only representative. The same process
ing can be achieved regardless of hoW the ambient and
monophonic components of a pair of signals are isolated.
The output of the multiplier 332 is fed directly to the left
mixer 280 and to the right mixer 284. Also, the original
FIG. 9. The curve 350 can be referred to as a spatial
sound stage generated from a pair of audio signals by
selectively enhancing the sound information that provides a
65
sense of spaciousness.
The enhancement circuits 306 and 320 modify the ambi
ent and monophonic components, respectively, of the sur
5,912,976
11
12
round signals SL and SR. In accordance With a preferred
embodiment, the transfer functions P2 and P3 are equal and
both apply the same level of perspective equalization to the
respect to that applied to ML—MR. This is required since the
normal frequency response of the human ear for sounds
directed at a listener from Zero degrees aZimuth Will empha
corresponding input signal. In particular, the circuit 306
siZe sounds centered around approximately 2.75 kHZ. The
emphasis of these sounds results from the inherent transfer
function of the average human pinna and from ear canal
equaliZes an ambient component of the surround signals,
represented by the signal SL—SR, While the circuit 320
equaliZes an monophonic component of the surround
resonance. The perspective curve 352 of FIG. 10 counteracts
the inherent transfer function of the ear to create the per
signals, represented by the signal SL+SR. The level of
equalization is represented by the frequency response curve
352 of FIG. 10.
The perspective equaliZation curves 350 and 352 are
displayed in FIGS. 9 and 10, respectively, as a function of
10
maintain the perception of a broad rear sound stage as if
displayed in log format. The gain level in decibels at
reference signal since ?nal ampli?cation of the overall
output signals occurs in the ?nal mixing process. Referring
initially to FIG. 9, and according to a preferred embodiment,
the perspective curve 350 has a peak gain at a pointAlocated
at approximately 125 HZ. The gain of the perspective curve
350 decreases above and beloW 125 HZ at a rate of approxi
mately 6 dB per octave. The perspective curve 350 reaches
a minimum gain at a point B Within a range of approximately
out of phase to the corresponding mixers 280 and 284 to
reproduced by phantom speakers 215 and 216.
gain, measured in decibels, against audible frequencies
individual frequencies are only relevant as they relate to a
ception of rear speakers for the signals SL—SR and SL+SR.
The resultant processed difference signal (SL— R)P is driven
15
By separating the surround signal processing into sum and
difference components, greater control is provided by alloW
ing the gain of each signal, SL—SR and SL+SR, to be adjusted
separately. The present invention also recogniZes that cre
ation of a center rear phantom speaker 218, as shoWn in FIG.
20
7, requires similar processing of the sum signal SL+SR since
the sounds actually emanate from forWard speakers 206 and
208. Accordingly, the signal SL+SR is also equaliZed by the
circuit 320 according to the curve 352 of FIG. 10. The
resultant processed signal (SL+SR)P is driven in-phase to
achieve the perceived phantom speaker 218 as if the tWo
phantom rear speakers 215 and 216 actually existed. For
1.5—2.5 kHZ. The gain increases at frequencies above point
B at a rate of approximately 6 dB per octave up to a point 25 audio reproduction systems Which include a dedicated center
C at approximately 7 kHZ, and then continues to increase up
to approximately 20 kHZ, i.e., approximately the highest
channel speaker, the circuit 250 of FIG. 8 can be modi?ed
so that the center signal C is fed directly to such center
frequency audible to the human ear.
Referring noW to FIG. 10, and according to a preferred
embodiment, the perspective curve 352 has a peak gain at a
speaker instead of being mixed at the mixers 280 and 284.
The approximate relative gain values of the various
signals Within the circuit 250 can be measured against a 0 dB
30
point A located at approximately 125 HZ. The gain of the
reference for the difference signals exiting the multipliers
perspective curve 350 decreases beloW 125 HZ at a rate of
272 and 308. With such a reference, the gain of the ampli
?ers 290, 292, 330, and 334 in accordance With a preferred
embodiment is approximately —18 dB, the gain of the sum
approximately 6 dB per octave and decreases above 125 HZ
at a rate of approximately 6 dB per octave. The perspective
curve 352 reaches a minimum gain at a point B Within a 35
range of approximately 1.5—2.5 kHZ. The gain increases at
frequencies above point B at a rate of approximately 6 dB
per octave up to a maximum-gain point C at approximately
10.5—11.5 kHZ. The frequency response of the curve 352
decreases at frequencies above approximately 11.5 kHZ.
Apparatus and methods suitable for implementing the
40
45
are disclosed in Us. Pat. Nos. 4,738,669 and 4,866,744,
issued to Arnold I. Klayman, both of Which are also incor
porated by reference as though fully set forth herein.
In operation, the circuit 250 of FIG. 8 uniquely functions
to position the ?ve main channel signals, ML, MR, C, SR, and
SL about a listener upon reproduction by only tWo speakers.
55
the speakers 206 and 208 shoWn in FIG. 7. This is accom
60
signal strength for the various signals of FIG. 8 is also
affected by the volume adjustments and the level of mixing
applied by the mixers 280 and 284.
65
produce a much improved audio effect because ambient
sounds are selectively emphasiZed to fully encompass a
listener Within a reproduced sound stage. Ignoring the rela
tive gains of the individual components, the audio output
plished through selective equaliZation of the ambient signal
Accordingly, the audio output signals LOUT and ROUT
applied to the signal SL —SR to broaden and spatially enhance
the ambient sounds from the signals SL and SR. In addition,
hoWever, the equaliZation curve 352 modi?es the signal
SL—SR to account for HRTF positioning to obtain the per
ception of rear speakers 215 and 216 of FIG. 7. As a result,
the curve 352 contains a higher level of emphasis of the loW
and high frequency components of the signal SL—SR With
at desired levels. In fact, if the level adjustment of multi
pliers 308 and 332 are desirably With the rear signal input
levels, then it is possible to connect the enhancement circuits
directly to the input signals SL and SR. As can be appreciated
by one of ordinary skill in the art, the ?nal ratio of individual
perception of a Wide forWard sound stage emanating from
information to emphasiZe the loW and high frequency com
ponents. Similarly, the equaliZation curve 352 of FIG. 10 is
to the type of sound reproduced and tailored to a user’s
personal preferences. An increase in the level of a sum signal
emphasiZes the audio signals appearing at a center stage
positioned betWeen a pair of speakers. Conversely, an
increase in the level of a difference signal emphasiZes the
ambient sound information creating the perception of a
Wider sound image. In some audio arrangements Where the
parameters of music type and system con?guration are
knoWn, or Where manual adjustment is not practical, the
multipliers 272, 286, 308, and 332 may be preset and ?xed
As discussed previously, the curve 350 of FIG. 9 applied to
the signal ML—MR broadens and spatially enhances ambient
sounds from the signals ML and MR. This creates the
user preferences and may be varied Without departing from
the spirit of the invention. Adjustment of the multipliers 272,
286, 308, and 332 alloWs the processed signals to be tailored
equaliZation curves 350 and 352 of FIGS. 9 and 10 are
similar to those disclosed in pending application Ser. No.
08/430751 ?led on Apr. 27, 1995, Which is incorporated
herein by reference as though fully set forth. Related audio
enhancement techniques for enhancing ambient information
signal exiting the ampli?er 332 is approximately —20 dB, the
gain of the sum signal exiting the ampli?er 286 is approxi
mately —20 dB, and the gain of the center channel signal
exiting the ampli?er 258 is approximately —7 dB. These
relative gain values are purely design choices based upon
signals LOUT and ROUT are represented by the folloWing
mathematical formulas:
5,912,976
13
14
The enhanced output signals represented above may be
and B, and points B and C. In a surround sound environment,
a gain separation much larger than 9 dB may tend to reduce
a listener’s perception of mid-range de?nition.
Implementation of the perspective curve by a digital
signal processor Will, in most cases, more accurately re?ect
the design constraints discussed above. For an analog
implementation, it is acceptable if the frequencies corre
(2)
magnetically or electronically stored on various recording
media, such as vinyl records, compact discs, digital or
analog audio tape, or computer data storage media.
Enhanced audio output signals Which have been stored may
then be reproduced by a conventional stereo reproduction
sponding to points A, B, and C, and the constraints on gain
separation, vary by plus or minus 20 percent. Such deviation
from the ideal speci?cations Will still produce the desired
enhancement effect, although With less than optimum
system to achieve the same level of stereo image enhance
ment.
Referring to FIG. 11, a schematic block diagram is shoWn
of a circuit for implementing the equalization curve 350 of
FIG. 9 in accordance With a preferred embodiment. The
circuit 270 inputs the ambient signal ML—MR, corresponding
15
to that found at path 268 of FIG. 8. The signal ML—MR is ?rst
conditioned by a high-pass ?lter 360 having a cutoff
frequency, or —3 dB frequency, of approximately 50 HZ. Use
of the ?lter 360 is designed to avoid over-ampli?cation of
the bass components present in the signal ML—MR.
The output of the ?lter 360 is split into three separate
signal paths 362, 364, and 366 in order to spectrally shape
the ambient signal SL—SR, corresponding to that found at
path 304 of FIG. 8. The signal SL—SR is ?rst conditioned by
a high-pass ?lter 380 having a cutoff frequency of approxi
the signal ML—MR. Speci?cally, ML—MR is transmitted
mately 50 HZ. As in the circuit 270 of FIG. 11, the output of
along the path 362 to an ampli?er 368 and then on to a
summing junction 378. The signal ML—MR is also transmit
results.
Referring noW to FIG. 12, a schematic block diagram is
shoWn of a circuit for implementing the equaliZation curve
352 of FIG. 10 in accordance With a preferred embodiment.
Although the same curve 352 is used to shape the signals
SL-SR and SL +SR, for ease of discussion purposes, reference
is made in FIG. 12 only to the circuit enhancement device
306. In a preferred embodiment, the characteristics of the
device 306 is identical to that of 320. The circuit 306 inputs
25
ted along the path 364 to a loW-pass ?lter 370, then to an
ampli?er 372, and ?nally to the summing junction 378.
Lastly, the signal ML—MR is transmitted along the path 366
the ?lter 380 is split into three separate signal paths 382,
384, and 386 in order to spectrally shape the signal SL—SR.
Speci?cally, the signal SL— R is transmitted along the path
382 to an ampli?er 388 and then on to a summing junction
to a high-pass ?lter 374, then to an ampli?er 376, and then
to the summing junction 378. Each of the separately con
ditioned signals ML— R are combined at the summing
396. The signal SL—SR is also transmitted along the path 384
junction 378 to create the processed difference signal (ML
MR)P. In a preferred embodiment, the loW-pass ?lter 370 has
?nally to the summing junction 396. Lastly, the signal SL—SR
is transmitted along the path 386 to a loW-pass ?lter 398,
a cutoff frequency of approximately 200 HZ While the
high-pass ?lter 374 has a cutoff frequency of approximately
to a high-pass ?lter 390 and then to a loW-pass ?lter 392. The
output of the ?lter 392 is transmitted to an ampli?er 394, and
35
7 kHZ. The exact cutoff frequencies are not critical so long
as the ambient components in a loW and high frequency
range, relative to those in a mid-frequency range of approxi
mately 1 to 3 kHZ, are ampli?ed. The ?lters 360, 370, and
374 are all ?rst order ?lters to reduce complexity and cost
but may conceivably be higher order ?lters if the level of
processing, represented in FIGS. 9 and 10, is not signi?
cantly altered. Also in accordance With a preferred
embodiment, the ampli?er 368 Will have an approximate
gain of one-half, the ampli?er 372 Will have a gain of
approximately 1.4, and the ampli?er 376 Will have an
then to an ampli?er 400, and then to the summing junction
396. Each of the separately conditioned signals SL—SR are
combined at the summing junction 396 to create the pro
cessed difference signal (SL—SR)P. In a preferred
embodiment, the high-pass ?lter 370 has a cutoff frequency
of approximately 21 kHZ While the loW-pass ?lter 392 has a
cutoff frequency of approximately 8 kHZ. The ?lter 392
serves to create the maximum-gain point C of FIG. 10 and
may be removed if desired. Additionally, the loW-pass ?lter
45
398 has a cutoff frequency of approximately 225 HZ. As can
be appreciated by one of ordinary skill in the art, there are
many additional ?lter combinations Which can achieve the
frequency response curve 352 shoWn in FIG. 10 Without
approximate gain of unity.
departing from the spirit of the invention. For example, the
The signals Which exit the ampli?ers 368, 372, and 376
make up the components of the signal (ML—MR)P. The
overall spectral shaping, i.e., normaliZation, of the ambient
exact number of ?lters and the cutoff frequencies are not
critical so long as the signal SL—SR is equaliZed in accor
dance With FIG. 10. In a preferred embodiment, all of the
?lters 380, 390, 392, and 398 are ?rst order ?lters. Also in
accordance With a preferred embodiment, the ampli?er 388
signal ML—MR occurs as the summing junction 378 com
bines these signals. It is the processed signal (ML—MR)P
Which is mixed by the left mixer 280 (shoWn in FIG. 8) as
part of the output signal LOUT. Similarly, the inverted signal
(MR— L)P is mixed by the right mixer 284 (shoWn in FIG.
8) as part of the output signal ROUT.
55
Referring again to FIG. 9, in a preferred embodiment, the
gain separation betWeen points A and B of the perspective
curve 350 is ideally designed to be 9 dB, and the gain
separation betWeen points B and C should be approximately
6 dB. These ?gures are design constraints and the actual
?gures Will likely vary depending on the actual value of
components used for the circuit 270. If the gain of the
ampli?ers 368, 372, and 376 of FIG. 11 are ?xed, then the
perspective curve 350 Will remain constant. Adjustment of
the ampli?er 368 Will tend to adjust the amplitude level of
point B thus varying the gain separation betWeen points A
Will have an approximate gain of 0.1, the ampli?er 394 Will
have a gain of approximately 1.8, and the ampli?er 400 Will
have an approximate gain of 0.8. It is the processed signal
(SL—SR)P Which is mixed by the left mixer 280 (shoWn in
FIG. 8) as part of the output signal LOUT. Similarly, the
inverted signal (SR—SL)P is mixed by the right mixer 284
(shoWn in FIG. 8) as part of the output signal ROUT.
Referring again to FIG. 10, in a preferred embodiment,
65
the gain separation betWeen points A and B of the perspec
tive curve 352 is ideally designed to be 18 dB, and the gain
separation betWeen points B and C should be approximately
10 dB. These ?gures are design constraints and the actual
?gures Will likely vary depending on the actual value of
components used for the circuits 306 and 320. If the gain of
the ampli?ers 388, 394, and 400 of FIG. 12 are ?xed, then
5,912,976
15
16
the perspective curve 352 Will remain constant. Adjustment
located Within the front sound stage, and Wherein said center
of the ampli?er 388 Will tend to adjust the amplitude level
of point B of the curve 352, thus varying the gain separation
betWeen points A and B, and points B and C.
channel signal is combined With a monophonic component
of the main left and right signals by said signal mixer to
generate said left and right output signals.
Through the foregoing description and accompanying
4. The system of claim 1 Wherein said at least four discrete
draWings, the present invention has been shoWn to have
important advantages over current audio reproduction and
enhancement systems. While the above detailed description
has shoWn, described, and pointed out the fundamental
novel features of the invention, it Will be understood that
various omissions and substitutions and changes in the form
and details of the device illustrated may be made by those
skilled in the art, Without departing from the spirit of the
invention. Therefore, the invention should be limited in its
audio signals comprises a center channel signal having
scope only by the folloWing claims.
What is claimed is:
1. A system for processing at least four discrete audio
10
discrete audio signals When said left and right output signals
are acoustically reproduced.
6. The system of claim 1 Wherein said ?rst audio enhancer
15
mately 1 kHZ and above approximately 2 kHZ relative to
frequencies betWeen approximately 1 and 2 kHZ.
7. The system of claim 6 Wherein the peak gain applied to
boost said ambient component, relative to the gain applied
to said ambient component betWeen approximately 1 and 2
kHZ, is approximately 8 dB.
audio information intended for playback from a front sound
stage, and surround left and right signals containing audio
information intended for playback from a rear sound stage,
said system generating a pair of left and right output signals
system comprising:
8. The system of claim 1 Wherein said second and third
25
a ?rst electronic audio enhancer receiving said main left
and right signals, said ?rst audio enhancer processing
an ambient component of said main left and right
signals to create the perception of a broadened sound
image across the front sound stage When said left and
right output signals are reproduced by a pair of speak
ers positioned Within the front sound stage;
a second electronic audio enhancer receiving said sur
round left and right signals, said second audio enhancer
equaliZes said ambient component of said main left and right
signals by boosting said ambient component beloW approxi
signals including main left and right signals containing
for reproduction from the front sound stage to create the
perception of a three dimensional sound image Without the
need for actual speakers placed in the rear sound stage, said
center stage audio information Which is acoustically repro
duced by a dedicated center channel speaker.
5. The system of claim 1 Wherein said ?rst, second, and
third electronic audio enhancers apply an HRTF-based trans
fer function to a respective one of said discrete audio signals
for creating an apparent sound image corresponding to said
audio enhancers equaliZe said ambient and monophonic
components of said surround left and right signals by
boosting said ambient and monophonic components beloW
approximately 1 kHZ and above approximately 2 kHZ,
relative to frequencies betWeen approximately 1 and 2 kHZ.
9. The system of claim 8 Wherein the peak gain applied to
boost said ambient and monophonic components of said
surround left and right signals, relative to the gain applied to
said ambient and monophonic components betWeen
approximately 1 and 2 kHZ, is approximately 18 dB.
10. The system of claim 1 Wherein said ?rst, second, and
35 third electronic audio enhancers are formed upon a semi
processing an ambient component of said surround left
and right signals to create the perception of an acoustic
sound image across the rear sound stage When said left
conductor substrate.
and right output signals are reproduced by the pair of
speakers positioned Within the front sound stage;
Ware.
11. The system of claim 1 Wherein said ?rst, second, and
third electronic audio enhancers are implemented in soft
12. A multi-channel recording and playback apparatus
a third electronic audio enhancer receiving said surround
receives a plurality of individual audio signals and processes
left and right signals, said third audio enhancer pro
cessing a monophonic component of said surround left
and right signals to create the perception of an acoustic
said plurality of audio signals to provide ?rst and second
enhanced audio output signals for achieving an immersive
sound image at a center location of the rear sound stage 45
multi-channel recording apparatus comprising:
sound experience upon playback of said output signals, said
a plurality of parallel audio signal processing devices for
modifying the signal content of said individual audio
When said left and right output signals are reproduced
by the pair of speakers positioned Within the front
sound stage; and
a signal mixer for generating said left and right output
signals from the at least four discrete audio signals by
combining the processed ambient component from the
main left and right signals, the processed ambient
component for the surround left and right signals, and
the processed monophonic component from the sur
round left and right signals, Wherein said ambient
signals Wherein each parallel audio signal processing
device comprises:
a circuit for receiving tWo of said individual audio
signals and isolating an ambient component of said
tWo audio signals from a monophonic component of
said tWo audio signals;
positional processing means capable of electronically
55
out-of-phase relationship With respect to each other.
2. The system of claim 1 Wherein said at least four discrete
audio signals comprise a center channel signal containing
With respect to a listener; and
a multi-channel circuit mixer for combining said pro
audio information intended for playback by a front sound
stage center speaker, and Wherein said center channel signal
is combined by said signal mixer as part of said left and right
cessed monophonic components and ambient compo
nents generated by said plurality of positional process
output signals.
3. The system of claim 1 Wherein said at least four discrete
audio signals comprise a center channel signal containing
audio information intended for playback by a center speaker
applying a head related transfer function to each of
said ambient and monophonic components of said
tWo audio signals to generate processed ambient and
monophonic components, said head related transfer
functions corresponding to a desired spatial location
components of said main and surround signals are
included in the left and right output signals in an
ing means to generate said enhanced audio output
65
signals Wherein said processed ambient components
are combined in an out-of-phase relationship With
respect to said ?rst and second output signals.
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertisement