Bass management system for home theater equipment

Bass management system for home theater equipment
US006332026B1
(12) United States Patent
(10) Patent N0.:
(45) Date of Patent:
Kuusama et al.
(54)
BASS MANAGEMENT SYSTEM FOR HOME
THEATER EQUIPMENT
(75)
Inventors:
Juha Kuusama; Minna Juhola; Juha
,
,
glzaki
ayman
et a1. . . . .-
6,122,382 *
Tampere (F1)
Notice:
i
. . . . ..
6,009,179 * 12/1999 Wood et a1. .
Assigneez Flextronics Design Finland 0y,
(*)
Dec. 18,2001
5,257,313 * 10/1993 Fujishita et al. ..................... .. 381/18
5,459,790 * 10/1995 Sco?eld et a1. ..
381/25
5,680,464 * 10/1997 IWamatsu
381/18
Laaksonen’ an of Tampere (F1)
(73)
US 6,332,026 B1
381/17
9/2000 lida et al. ............................. .. 381/18
FOREIGN PATENT DOCUMENTS
Subject to any disclaimer, the term of this
patent is extended or adjusted under 35
0 546 619 A2
0 729 287 A2
6/1993 (EP) _
8/1996 (EP) .
U.S.C. 154(b) by 0 days.
(21)
Appl. N0.:
(22) PCT Filed?
86
(30)
'
y exammer
Primary Examiner—Xu Mei
PCT FI97 00466
Assistant Examiner—Brian Tyrone Pendleton
O
§ 371 Date:
(87)
't d b
C1 6
Aug- 5! 1997
PCT N .:
( )
*
09/043,681
/
/
May 1, 1998
(74) Attorney, Agent, or Firm—Burns, Doane, SWecker &
Mathis, L.L.P.
§ 102(e) Date: May 1, 1998
(57)
PCT Pub- No-3 W098/06239
_
A setup to be used in a home theater or sound reproduction
system for handling loW frequency sound signals With a
PCT Pub' Date' Feb‘ 12’ 1998
Foreign Application Priority Data
signal source providing several full bandwidth digital sound
channels and at least one digital lOW frequency subWoofer
hillgzg,
.................................................... ..
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.................................................... ..
,
ABSTRACT
channel includes a delay-and level control unit at least for
each full bandwidth Signal Channel, Which is equipped for a
Speaker not Capable of reproducing low frequency Sounds‘ A
(51)
(52)
Int. Cl.7 ..................................................... .. H04R 5/00
US. Cl. ........................... .. 381/17; 381/104; 381/307
?rst summing stage creates the sum channel by summing the
delay-and level Controlled signal rshannols~ A second sum
(58)
Field of Search ................................ .. 381/18, 19, 20,
ming Stage adfls a low frequency subwpofer Channel to the
381/27, 104, 307
sum channel in order to create a digital bass channel. A
DA-conversion, amplifying, loWpass-?ltering and volume
(56)
References Cited
control unit processes the digital bass channel in order to
create an analog bass channel.
U.S. PATENT DOCUMENTS
5,200,709 *
4/1993 Saito et a1. ......................... .. 330/126
2 Claims, 2 Drawing Sheets
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US 6,332,026 B1
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US 6,332,026 B1
1
2
BASS MANAGEMENT SYSTEM FOR HOME
even damage these speakers. One of the functions of a home
theater device is therefore to extract loW bass signals from
THEATER EQUIPMENT
small speaker output signals and to redirect them to large
speakers capable of reproducing them. This function is
called bass management (block 114 in FIG. 1).
BACKGROUND OF THE INVENTION
1. Field of the Invention
The innovation is a setup in home theater or other sound
In most home theater devices bass management is realiZed
With analog ?lters and sWitches. This approach is very
straight forWard to build and is directly compatible With eg.
reproduction equipment to be used for handling loW fre
quency audio signals With an audio signal source producing
several digital full bandWidth audio channels and possibly in
addition to these one or several digital loW frequency
sub-Woofer channels.
2. Description of the Related Art
As laserdisc players and hi?-VCR’s have groWn popular,
also the so called home theater setups have become
Widespread, especially in USA. Such a setup typically
includes a large screen television, laserdisc player and/or
the Dolby con?guration de?nitions. Disadvantages of this
10
approach are the limited ?exibility resulting from ?xed
sWitches and unclarity from the user’s point of vieW. There
fore most home theater devices can only perform con?gu
rations 1 and 2 of the Dolby license de?nitions, some of
15
from all possible combinations of large and small speakers
them con?guration 3 as Well. The user can not choose freely
and also the user has to knoW and understand the meaning
of Dolby con?gurations 1, 2 and 3 (Dolby AC-3 licensee
information manual, version 1.0, ?gures 9.6, 9.7 and 9.8; all
VCR and a sound reproduction system consisting of sur
round sound decoder, multi-channel audio ampli?er and
speakers. In addition to the usual tWo main front speakers
blocks are analog).
The limitations of analog bass management are easy to
overcome by carrying out the necessary ?ltering and sum
ming in digital domain. In this case the user interface for
there is a center speaker betWeen them, one or tWo surround
speakers situated behind or on sides of the listeners and
possibly also a separate subWoofer speaker for reproduction
of loW bass signals.
A simpli?ed block diagram of a home theater setup is
25
presented in FIG. 1. For the sake of clarity, user and control
large/small/none, SubWoofer: yes/no”. NoW at its best the
bass management for one channel may be performed as
interfaces, volume control (placed either in digital domain in
described in FIG. 2. This entity described in FIG. 2 is
unlikely to have been presented before and is placed for each
channel in the processing unit 112 in FIG. 1. The result is
that the processing unit is only folloWed by a six-channel
conjunction With DA-converters or after the bass
management) and poWer ampli?ers have been left out of the
?gure. The setup in FIG. 1 consists of input stage 100, into
Which both several analog inputs 101, 102, 103 and several
digital inputs 104, 105, 106 may be connected. In each case
the input signal is selected With signal source selectors 107
and 108, respectively for analog and digital input sources.
After this the analog input signal is AD-converted With
AD-converter 109 and digital input signal is handled With
de?ning the speaker con?guration is intuitively: “Front
Main: large/small, Center: large/small/none, Surrounds:
DA-converter 113 While bass management unit 114 is left
out as obsolete.
35
In FIG. 2 the incoming digital signals for left front
speaker, center speaker, right front speaker, left surround
speaker, right surround speaker and subWoofer speaker have
been marked 201—206. These signals are fed to complemen
digital audio receiver 110. From these tWo digital signals one
is selected With source selector 111, folloWed by the pro
cessor unit 112 Which Will perform the desired processing to
tary ?lters 207—211, Which divide the incoming signals to
“high” and “loW ” output signals, some of Which equals the
the digital audio signal. This processing may include such
incoming signal except for slight processing delay. These ten
steps as Dolby Digital (previously Dolby AC-3) decoding,
output signals as Well as the subWoofer output signal are
Dolby Pro Logic decoding, THX post processing, room
driven through adjustable amplifying stages 212—222 to
simulations, tone controls etc. After these processing steps
these typically six digital audio signals are DA-converted.
The number of channels varies betWeen different systems;
summing stage 223 to generate output signal 224 for one
speaker. With summing stages 212—222 the output signal for
45
for instance there may be from 1 up to 4 or 6 surround
channels and also there may be more than one center
channels. After the DA-conversion there has to be the so
Controlled by speaker con?guration sWitches a large
only gets “high” output signals, Which lack the loW bass
sounds. These Will be directed to large speakers. Also
leaving a speaker completely off the design is possible. In
result, output signals for left front speaker, center speaker,
right front speaker, left surround speaker, right surround
this case the signal of eg. missing center speaker may be
divided betWeen the tWo main front speakers. Also When
bass sounds are divided to several speakers for reproduction
55
The bene?ts of this approach also include perfect control
of processing delays and thus the signal delays experienced
by the listener, and the fact that the sound ?eld may be
controlled by peculiar Ways eg. by shifting it 90 or 180
degrees.
There is also loW bass material in movie soundtracks. In
many cases it is not practical to have six large speakers in a
home theater setup. An example of a more practical solution
frequency signals; high level loW frequency signals may
(eg. con?guration With several large speakers but no
subWoofer) the correct level for bass sounds can be set.
speaker capable of reproducing at least most of the audio
bandWidth, ie. both loW bass signals and high treble sounds.
“Small tWeeter speaker” refers to a speaker Which is only
able to reproduce high frequencies and no loW bass signals.
is to have large front main speakers Whereas the other
speakers are small. Small speakers can not reproduce loW
bandWidth input signals.
speaker gets both “high ” and “loW” outputs. Asmall speaker
called bass management in block 114, to avoid feeding
strong bass signals to speakers unable to handle them. As a
speaker and subWoofer are generated. These outputs are
labelled 115—120 in FIG. 1.
Let us note, that in this context the Word speaker refers to
a typically enclosed entity consisting of one or several
speaker elements. “Large or full range speaker” refers to a
each speaker may be ?exibly set as combination of full
65
In practice some summing coefficients are alWays Zero eg.
right channel signals are never redirected to left channel, and
subWoofer never gets any high sounds. To save processing
poWer the system described in FIG. 2 needs not to be
implemented completely. It may also be carried out With
appropriate combinations of ordinary non-complementary
US 6,332,026 B1
4
3
?lters in Which the signal is suitably fed, even if the
Best features of the previously described bass manage
processing block diagram Would be substantially different
ment methods may be combined With a setup in Which all
from the one described above.
necessary ?lters and delays are done digitally but signal
Even though digital bass management has many bene?ts
it also has its drawbacks especially When using Dolby AC-3
system (also knoWn as Dolby Digital). This system includes
summing at least mostly in,analog domain. By doing this the
a separate subWoofer channel Which by de?nition is to be
reproduced ten desibels (10 dB=3.16) louder than the other
channels. Since the dynamic range of DA-converters is
limited the sound quality may then deteriorate. Let us
assume for example a speaker con?guration With large main
front speakers, small other speakers and no subWoofer
speaker in a situation in Which the incoming signal has full
amplitude bass sound in every channel. If reference level for
full amplitude signal is said to be 1 then the summed bass
signal level of surround speakers is 2, center channel bass
signal level is 1 and subWoofer channel signal level is 3.16,
and the summed redirected bass signal level is thus 3.16+
2+1=6.16. When this is divided equally to left and right main
front speakers the signal level of these channels becomes
1+(6.16/2)=4.08=4.08=+12.2 dB. In order to avoid overdriv
ing the DA-converters under any circumstances the signal
10
Which are able to reproduce full bandWidth sound signals.
BRIEF DESCRIPTION OF THE DRAWINGS
15
In the folloWing this innovation is presented in more
detail With reference to the accompanying draWing in Which
FIG. 1 shoWs a simpli?ed block diagram of a traditional
home theater setup,
FIG. 2 shoWs the block diagram of digital bass manage
ment in principal, and
FIG. 3 describes the setup according to the invention for
level has to be reduced 12.2 desibels before DA-converters.
The Worst case is a speaker con?guration With no subWoofer
and in Which only the center channel is large resulting in a
need to reduce the signal level by 18.2 dB. This leads to
?exibility of a digital system is maintained and the dynamic
range of DA-converters can be fully exploited.
Economically the setup complying With this innovation
also includes either sWitching and summing stages or adjust
able volume control and summing stages to combine the
analog bass channel to the analog signals going to speakers
25
deterioration of sound quality.
bass management in home theater setup as a block diagram.
Also the interfacing of the bass channel to one other channel
is presented, in this case the left front channel. The signal
redirection has been left out from this ?gure to maintain
clarity.
The 18 or 20 bit DA-converters currently Widely in use
DETAILED DESCRIPTION OF THE
INVENTION
have dynamic range of about 85—95 dB. When signal level
is dropped before DA-converters their limited dynamic
range is not fully exploited (12—18 dB equals 2—3 bits).
The purpose of the present invention is to present a bass
Inputs for this setup are the digital sound signals divided
in the folloWing six channels: left front channel L, right front
channel R, left surround channel LS, right surround channel
RS, center channel C and subWoofer channel S. These signal
inputs may be generated for example in block 112 in FIG. 1
and they comply With the signals in use for example in
Dolby Digital (Dolby AC-3 ) system. In FIG. 3 the left front
management setup Which combines the bene?ts of both
setups described earlier. This is achieved by a setup accord
ing to the present invention the ?rst embodiment of Which is
high-pass ?lter 14 through Which the signal goes if the front
speakers are small, before the signal is fed to sWitch 15.
It is also inconvenient for the user if the output signal
level varies substantially betWeen different speaker con?gu
rations. For instance determining correct amplifying poWer
and sensitivity is almost impossible.
35
SUMMARY OF THE INVENTION
channel L has been presented completely. It consists of a
Equal building blocks (not presented) also exist for right and
characteriZed by comprising
center channels as Well as both surround channels. If any
a delay and level control unit for at least every full
bandWidth signal channel equipped With a speaker unable to
reproduce loW pitch sounds;
a ?rst summing stage for summing the delay and level
45
summed to the bass channel to be described in more detail
controlled signal channels to create a sum channel;
later, but instead the high-pass-?lter 14 is bypassed and the
signal fed directly to sWitch 15 directing the signal to
summing stage 13 through DA-converter and volume con
trol unit 16. In summing stage 13 the bass channel is
a second summing stage for summing the loW frequency
subWoofer channel into the sum channel to create a digital
bass channel and
a DA-converter-, amplifying-loW-pass ?ltering- and vol
summed to this signal in order to create the signal directed
ume control unit to perform these functions to the digital
bass channel in order to create an analog bass channel.
The second embodiment of the invention is characteriZed
by comprising
speci?c speaker is small, the loW bass frequencies are taken
aWay from its signal by high-pass ?ltering. If hoWever a
speaker is large the signal is neither high-pass ?ltered nor
to this speci?c large speaker.
55
a delay and level control unit for at least every full
bandWidth signal channel equipped With a speaker unable to
reproduce loW pitch sounds;
In order to create the bass management in a setup accord
ing to the invention a bass channel is created from the
signals of those channels in Which the speakers are small and
the subWoofer channel S. In the setup presented in FIG. 1
any of the channels L, R. LS, RS and C can be WithdraWn
the bass channel. In this setup the level balance betWeen the
a ?rst summing stage for summing the delay and level
signals and delays is ?rst adjusted in a delay-and level
controlled signal channels to create a sum channel
a loW pass ?lter for the sum channel a second summing
summed in a summing stage 6 to create the sum channel SC.
stage to sum the loW frequency subWoofer channel to the
loW frequency ?ltered sum channel to create a digital bass
channel and
a DA-converter-, amplifying- and volume control unit to
control unit 1 . . . 5 respectively. After this the signals are
Also in this setup the signals from large speakers are not
added in the sum channel by setting their ampli?cation to
65
Zero in the delay-and level control unit. SubWoofer channel
S signal is then added to the summed and possibly loW
perform these functions to the digital bass channel in order
pass-?ltered (7) signal creating the digital bass channel
to create an analog bass channel.
signal DB. This signal is processed in DA-converter-,
US 6,332,026 B1
5
6
ampli?cation-, loW pass-?ltering- and volume control unit 9
to create analog bass channel AB. This signal is directed
therefore understandable that it may be altered in various
Ways based on the bass management philosophy Without,
primarily to subWoofer channel 19 if there is a subWoofer in
the system. If there is no subWoofer the signal is directed to
hoWever, differeing from the scope of the protection de?ned
in the attached patent claims.
What is claimed is:
large speakers. One loW pass?lter is enough for the bass
channel signal and it can be done either digitally in unit 7 or
1. A setup to be used in a home theater or other sound
in analog domain in unit 9, ie. either before DA-conversion
reproduction system for handling loW frequency sound
or after it.
signals, comprising:
When analog bass channel is directed to large speakers
instead of the missing subWoofer speakers, sWitches 10, 11
a signal source providing several full bandWidth digital
sound channels;
and 12 of FIG. 3 are used to direct the bass channel for
summing in left and right front channel 17 and 18, surround
at least one digital loW frequency subWoofer channel;
channel 20 or center channel 21 depending on Which speak
a delay-and level control unit at least for each full
ers of these are large. Summing is done in summing stages
of Which only the left front channel summing stage 13 is
presented. It is possible for left and right front channel as
Well as left and right surround channel speakers to be
different from each other, ie. one small and one large, but
this deteriorates the sound quality. In this case, hoWever, the
15
sounds;
summing the delay-and level controlled signal chan
nels;
each front speaker and one for each surround speaker,
a second summing stage to add the loW frequency sub
respectively.
Woofer channel to the sum channel in order to create
one digital bass channel;
Let us note that the analog sWitches 10, 11 and 12 can be
replaced by a volume control. In this case no attenuation/
25
bass channel level control is done in this volume control.
Also, in this case the dynamic range of the bass channel
The bene?ts of the setup complying With this innovation
are:
Only a minor amount of processing poWer is required,
maximum 5 high pass-?lters and 1 loW pass-?lter. And the
loWpass-?lter can be performed in analog domain if
signals.
required.
reproduction system for handling loW frequency sound
signals, comprising:
a signal source providing several full bandWidth digital
able dynamic range. Even if the bass signal of some
sound channels;
individual channels in some cases has to be attenuated the
at least one digital loW frequency subWoofer channel;
sound quality is not deteriorated because the noise spec
trum of the noise generated in a DA-comverter is spread
to the Whole audio band. Since in any case only the loW
a delay-and level control unit at least for each full
bandWidth signal channel, Which is equipped With a
speaker not capable of reproducing loW frequency
sounds;
a ?rst summing stage for creating a sum channel by
45
summing the delay-and level controlled signal chan
nels;
The ?exibility of digital setup is maintained.
The method for handling different channel signals in a
setup complying With this invention may be summariZed in
a second summing stage to add the loW frequency sub
Woofer channel to the sum channel in order to create
the folloWing bass management philosophy.
one digital bass channel;
1: If a speaker is large nothing is done to the signal.
2: If a speaker is small the signal is high-pass-?ltered and
simultaneously summed to the subWoofer signal With
amplitude depending on speaker con?guration to create
a bass channel. Bass channel is loWpass-?ltered. If
there is a subWoofer speaker in the system the bass
volume control unit to process the digital bass channel
in order to create an analog bass channel; and
2. A setup to be used in a home theater or other sound
There is allWays full amplitude signal in DA-converters
except in the bass channel taking advantage of all avail
after DA-conversion.
a DA-conversion-, amplifying-, loWpass-?ltering-and
sWitch means disposed betWeen speakers capable of
reproducing full bandWidth sound signals and the ana
log bass channel, and summing means for combining
the analog bass channel to analog signals directed to
speakers capable of reproducing full bandWidth sound
DA-converter is alWays fully exploited.
frequencies are required from the signal in the bass
channel DA-converter most of the signal spectrum and
therefore also most of the noise may be loWpass-?ltered
speaker not capable of reproducing loW frequency
a ?rst summing stage for creating a sum channel by
number of sWitches 10 and 11 has to be doubled, one for
level control is needed in digital summing stage since the
bandWidth signal channel, Which is equipped With a
a DA-conversion-, amplifying-, loWpass-?ltering-and
volume control unit to process the digital bass channel
in order to create an analog bass channel; and
adjustable volume control means disposed betWeen
55
speakers capable of reproducing full bandWidth sound
signals and the analog bass channel, and summing
channel is directed to it. If there is no subWoofer
means for combining the analog bass channel to analog
speaker the bass channel is summed to the signals
signals directed to speakers capable of reproducing full
bandWidth sound signals.
directed to large speakers.
The setup complying With this innovation is above
described With only one explanatory example and it is
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