an) ow
US007664276B2
(12) Ulllted States Patent
(10) Patent N0.:
McKee Cooper
(54)
(45) Date of Patent:
Feb. 16, 2010
MULTIPASS PARAMETRIC OR GRAPHIC EQ
5,930,370 A
7/1999 Ruzicka ..................... .. 381/ 18
FITTING
6,253,293 B1
6/2001
Rao et al. ................. .. 711/147
6,639,989 B1*
10/2003
Zacharov et a1. .......... .. 381/103
6,655,212 B2
6,721,428 B1
12/2003 Ohta .............. ..
.. . 73/586
4/2004 Allred et a1. .............. .. 381/103
(75)
Inventor:
(73)
Assignee: Cirrus Logic, Inc-, Austin, TX (U S)
Joel C. McKee Cooper, Lafayette, CO
(US)
(*)
Notice:
7,529,377 B2 *
2004/0258259 A1
Subject to any disclaimer, the term of this
patent is extended or adjusted under 35
U.S.C. 154(b) by 1014 days.
Devices, Inc. One Technology Way, PO. Box 9106, NorWood, MA
020629106
(Continued)
Prior Publication Data
Us 2006/0062405 A1
Nackvi et a1. ............. .. 381/103
SHARC Melody Platform W1th Auto Room Tuner (ART) Technol
ogy, Analog Devices, wwwanalogcom/SHARC, © 2004, Analog
Appl' NO" 11/057’367
Filed:
Feb. 15, 2005
(65)
5/2009
12/2004 Koyama ................... .. 381/307
OTHER PUBLICATIONS
_
_
(21)
(22)
US 7,664,276 B2
Primary ExamineriXu Mei
(74) Attorney, Agent, or FirmiRobert Platt Bell; Steven Lin
Mar‘ 23’ 2006
Related US. Application Data
(57)
ABSTRACT
(63) Continuation-in-part of application No. 11/038,577,
?le? on, JaHNZ 1 ’1
app lcanon
0'
ililci’innmgnog'lggoef of
’
’
e
on
e0‘
’
Multiple passes are executed in the setup of an equalizer, and
'
modi?cation of the equalization is performed after each pass
(60)
Provisional application No, 60/612,474, ?led on sell
23s 2004_
(51)
Int. Cl.
H03G 5/00
(2006.01)
of an analysis phase. After an initial pass, the equalization is
adjusted, based upon the location of peaks and valleys in the
system response. This initial adjustment of equalization may
tend to ?atten most of the peaks and valleys to produce the
desired uniform linear response. Inexact application of equal
(52)
(58)
US. Cl. ................................... .. 381/103; 333/28 R
Field of Classi?cation Search ................. .. 381/56,
izatien Corrections may introduce other artifacts into the sys
tem response and/Or may not sufficiently normalize equaliza
381/58, 103; 333/28 R; 375/2292231
tion. A second pass is then performed to measure the system
See application ?le for Complete Search history
response using the neW equalization settings. The neW peaks
_
References Clted
and valleys are measured, and the equalization adjusted to try
to ?atten response further. A proximity range may be applied
U.S. PATENT DOCUMENTS
to each pass, to reduce the likelihood that adjustment of one
(56)
equalizer coe?icient Will create artifacts in the resulting sys
5,506,910 A *
4/1996
Miller etal. .............. .. 381/103
5,572,443 A *
11/1996
Emoto etal. .............. .. 702/103
5,768,398 A *
6/1998
Janse etal.
tem response.
18 Claims, 5 Drawing Sheets
............... .. 381/103
Digital
Dlgltal
Signal Source
on, DVD, HDTV,
Teams
5mm“
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215
205
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Signal
Decoder
l
Equalizer
l- 1L‘
m
1”
20
/
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2
an) ow
225
280 \
Equalizer
Coefficients
270
Frequency
Analyzer
i
System Response
M90
US 7,664,276 B2
Page 2
OTHER PUBLICATIONS
“Cirrus Logic’s Intelligent room Calibration Software Optimizes
Audio receiver System, Speaker Response for Ideal Sound Experi
ence”, http://WWW.cirrus.com/en/press/releases/P426.html, Oct. 5,
Transfer-Function Measurement With Maximum-Length Sequences,
Douglas D. Rife and John Vanderkoov, J. Audio Eng. Soc., vol. 37,
2004.
No.6, Jun. 1989.
Adaptive Signal Processing, Bernard WidroW, (c) 1985, Prentiss
An Efficient Algorithm for Measuring the Impulse Response Using
Hall, INc., Englewood Cliffs, New Jersey, 17632. ISBN 0-13-004029
Pseudorandom Noise, Jeffrey Borish and James B. Angell, J. Audio
01.
Eng. Soc., vol. 37, No. 7, Jul/Aug. 1983.
* cited by examiner
US. Patent
Feb. 16, 2010
Sheet 1 0f 5
US 7,664,276 B2
[-18
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SUB-WOOFER
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BASS SPEAKER
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25
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, REAR AMBIENCE
SPEAKER
Figure 1 (Prior Art)
24
/
RIGHT
SATELLITE
SPEAKER
US. Patent
Feb. 16, 2010
Sheet 2 0f5
Digital
Digital
Signal Source
co, DVD, HDTV,
Testing
Signal
etc.
215
US 7,664,276 B2
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270
System Response
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Feb. 16, 2010
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US 7,664,276 B2
1
2
MULTIPASS PARAMETRIC OR GRAPHIC EQ
FITTING
nal. Interconnect module 14 also outputs an audio signal to
front center speaker 20. Front center speaker 20 receives both
the left and right component signals of the stereophonic sig
nal and reproduces the (L+R) summation signal. Preferably,
CROSS-REFERENCE TO RELATED
APPLICATIONS
front center speaker 20 is located in proximity to television 12
SUBWOOFER DISTANCE MEASUREMENT”, ?led on
and projects the acoustic output of the (L+R) summation
signal toWard the listener 28.
Interconnect module 14 also outputs the left channel signal
to left satellite speaker 22 and right channel signal to right
satellite speaker 24. Left satellite speaker 22 and right satel
lite speaker 24 may be relatively small speakers and need only
reproduce mid range and/or high frequency signals. Left and
Dec. 3, 2004, and incorporated herein by reference. The
right satellite speakers are preferably oriented so that the
present application is also a Continuation-In-Part of US.
primary axis of radiation of the speaker points upWard along
patent application Ser. No. 11/038,577, ?led on Jan. 21, 2005,
a vertical axis; hoWever, other orientations of the satellite
The present application claims priority from Provisional
US. Patent Application No. 60/612,474 ?led on Sep. 23,
2004, and incorporated herein by reference. The present
application is also a Continuation-In-Part of US. patent
application Ser. No. 1 1/002,102 entitled “TECHNIQUE FOR
speakers may also provide satisfactory performance. Inter
and incorporated herein by reference.
connect module 14 also outputs an audio signal to rear ambi
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for
automatically equalizing a home theater or other audio sys
tem. In particular, the present invention is directed toWard a
ence speaker 26. Rear ambience speaker 26 typically receives
20
an audio signal in the form of a left channel minus right
channel (L-R) or a right channel minus left channel (R-L)
difference signal. As Will become apparent throughout this
detailed description, several embodiments of the invention
technique for providing continuous or active adaptation of the
described herein enable interconnect module 14 to generate a
equalization of a home theater or other audio system.
variety of signals to be output to left satellite speaker 22, right
25
satellite speaker 24, and/or rear ambience speaker 26. It
BACKGROUND OF THE INVENTION
should be noted at the outset that the term speaker refers to a
Home theater systems, Which once Were expensive luxury
items, are noW becoming commonplace entertainment
devices. Complete Home Theater systems, knoWn as a Home
put signals Where the system may include one or a number of
system for converting electrical input signals to acoustic out
crossover netWorks and/or transducers.
30
Theater In a Box (HTIB), are available to consumers at rea
The components described in FIG. 1 typically are arranged
to optimiZe the surround sound effect to enhance the listening
sonable prices. HoWever, properly setting up such Home The
experience of the vieWer 28. The vieWer 28 typically faces
ater systems can sometimes be problematic for the consumer.
television 12 Which has front center speaker 20 arranged in
proximity to television 12 so that center speaker 20 and tele
vision 12 radiate their respective audio and video output in the
general direction of vieWer 28. The left satellite speaker 22
typically is arranged to the left side of vieWer 28 While right
satellite speaker 24 is arranged to the right side of vieWer 28,
Home theater systems provide a number of components,
Which may be located in various parts of the room. The
components include the home theater receiver/ampli?er,
front stereo speakers (left and right), rear surround sound
speakers (left and right), a center speaker, and a subWoofer.
Various other combinations of speakers may also be used,
including additional or feWer speakers. One such home the
ater system is described, for example, in US. Pat. No. 5,930,
370, issued Jul. 27, 1999 to RuZicka, incorporated herein by
35
both satellite speakers typically being located nominally mid
40
reference.
FIG. 1 depicts a diagrammatic vieW of the home theater
surround sound speaker system (the surround sound system)
45
10 arranged in accordance With the principles of the present
invention. The surround sound system 10 includes a source of
a preferably ampli?ed stereo signal, shoWn in FIG. 4 as tele
vision (“TV”) set 12. The stereo audio source may be any of
a number of audio signal sources. It should, thus, be noted that
50
the source of a stereo audio signal is represented herein as
television 12, but the audio signal source may also be a stereo
receiver, a car stereo, a portable compact disk or tape player,
a portable boom-box type stereo, or any other source of a
stereo signal.
Television 12 outputs an ampli?ed audio signal to inter
Way betWeen the vieWer 28 and television 12. Rear ambience
speaker 26, Which contributes to creating a spacious audio
effect, is typically located behind vieWer 28. Rear ambience
speaker 26 is depicted as a single speaker, but multiple rear
speakers 26 may be included in the system.
One problem With these home theater systems is in adjust
ing the equaliZation of the system to compensate for room
acoustics, speaker type, and other factors. Traditionally, a
consumer adjusted equaliZation using a so-called graphic
equaliZer, Where a number of narroW band-pass ?lters are
provided, each With a corresponding slide sWitch. The con
sumer adjusts each slide sWitch to attenuate or amplify a
particular frequency band. More modern systems may use
electronic displays in place of the slide sWitches, but the
overall functionality is the same.
55
The purpose of an equaliZer is to provide an audio response
that is generally “?at” across the entire frequency spectrum.
connect module 14 via a multi-conductor cable 16. Multi
Due to limitations in system and speaker design, as Well as
conductor cable 16 typically includes tWo conductor pairs for
conducting the left and right channels of the stereo signal
output by television 12 to interconnect module 14. Intercon
nect module 14 receives the audio signals from television 12
and assembles the component left and right channel signals
for selective distribution to particular component speakers of
the surround sound system 10.
The component speakers typically include a sub-Woofer
18, Which receives full range left and right signals, but only
room acoustics and interaction of room acoustics With
reproduces the loW frequency components of the audio sig
speaker design and placement, various frequency ranges in a
60
system may be attenuated or accentuated, resulting in a sound
65
reproduction Which is not faithful to the original recording.
A “?at” response generally refers to the resulting fre
quency versus amplitude graph. If the system is properly
equaliZed, the graph should look like a ?at line though all
frequency ranges. In reality, this goal is never entirely
achieved due to limitations of audio components and room
acoustics. HoWever, With a graphic equaliZer, it is possible to
US 7,664,276 B2
3
4
improve the response considerably such that the resulting
example of such a prior art equalization system is illustrated
in US. Pat. No. 6,721,428, issued Apr. 13, 2004 to Allred et
al. and incorporated herein by reference.
sound is a more faithful reproduction of the original sound.
The problem With manually operated graphic equalizers is
that the equalization is based upon the consumer setting the
various frequency levels based upon What the consumer hears
and What the consumer thinks Will create the proper equal
ization for the system. This manual solution is a largely
empirical approach, as many consumers cannot properly iso
late various frequencies “by ear” and understand hoW to
These prior art automatic equalization setup systems typi
cally have three phases. First, the system is analyzed from a
single position or multiple positions in the room, usually by
generating an audio signal through the speakers, and then
receiving the audio signal through a remote microphone or
the like to produce a system response. Second, the results of
such analysis are translated to a run-time equalization setup
and saved. Run-time equalization refers to the process of
adjust the equalizer properly. In addition, as the music type
and sound changes, as Well as the acoustic properties of the
room, the equalization set at one level may be inappropriate
for another audio environment.
equalizing the audio signal during the digital decoding stage.
Third, the saved settings are used by the equalizer at run-time
The early graphic equalizers generally had a ?xed number
of equalizer circuits, each adjusting a predetermined narroW
band of frequencies. HoWever, When attempting to equalize a
system, it becomes readily apparent that certain frequency
ranges may require ?ner incremental ranges of adjustment,
as an additional post-processing step to Whatever other audio
processor softWare is running at the time.
Examples of such other audio processor software include
DolbyTM DigitalTM AC-3, Digital Theater Systems (DTS),
Pulse Code Modulation (PCM), bass management, delay
Whereas Whole bands of frequencies can be adequately
adjusted using a single circuit. Proving additional equalizer
control or the like. These various digital audio processing
20
?lter elements and sWitches to solve this problem is prohibi
their respective producers, or comparable algorithms may be
devised. The equalization algorithms of the Prior Art may
thus be applied subsequent to the decoding step in the play
tively expensive. The parametric equalizer helps solve this
problem by alloWing a limited number of equalizer elements
to adjust audio levels in a ?exible manner. Each level adjust
ment may be itself adjusted to control a different frequency
range.
25
upon system response in the room.
The extent to Which the system can be corrected for the
for Width. Frequency ranges that require a ?ne granularity of
adjustment may be more precisely controlled using a number
30
frequency ranges that can be adjusted as a group can be
controlled With one single Wide-band element in the paramet
ric equalizer. In this manner, the parametric equalizer can
remains a dif?culty in the prior art as to hoW to best ?t a
35
control elements than a typical prior art ?xed-frequency ele
ment graphic equalizer. Again, hoWever, if a consumer
attempts to manually control equalization, the results are
often less than optimal, as the results are based upon the
ability of the consumer to discern different frequency ranges.
There are a number of prior solutions to the problem of
40
hardWare. For example, When decoding a digital data stream,
such as from a CD, DVD, or other digital audio source,
There are at least tWo problems With the curve-?tting tech
the term “system response” refers to the response of the
speaker and room) are at least partially due to phase-response
50
sical, rap, or for movie or DVD playback or the like. The
55
system. These pre-set levels do not take into account the room
acoustics and provide only limited choices to the consumer.
The consumer can only select the equalization setup that
response. The other part is the magnitude response (often
inaccurately called the “frequency response”), Which is the
poWer level (Y-axis, usually in dB) plotted against frequency
Qi-axis in Hz).
A second problem With the curve ?tting technique is the
60
affecting audio playback.
More recently, one of the more popular features for home
theater systems has been some form of automatic equaliza
tion setup to minimize adverse affects of speaker/room inter
actions. Most solutions, hoWever, involve a one-time setup
issues, Which may not respond in the desired manner to a
frequency-based solution. Applying a —3 dB equalization to a
3 dB peak may not ?atten the response as intended.
The “phase response” of the speaker in the room is a
function of frequency and is one part of the frequency
provide pre-set equalization levels for rock music, jazz, clas
sounds best for the given circumstances. The system is not
optimized for the room acoustics, speakers, and other factors
particular frequency range is too loW, it may be boosted.
nique. Quite often the peaks found in a system response (here,
Other systems are knoWn in the art Wherein home theater
equalization takes place in softWare Within the home theater
?tting a ?xed-band equalizer to a predetermined frequency
response. One solution is a straightforWard curve-?tting. For
an n-band equalizer, the algorithm ?nds the n highest peaks
and/or valleys in the frequency response and sets each band to
correct the corresponding feature. Thus, if a particular fre
quency range is too high, it may be attenuated, and if a
45
softWare as Well as in hardWare, or in a combination of both.
systems, particularly more loW-end units, provide a limited
number of pre-set equalization patterns for different music
types and listening styles. Thus, a home theater system may
?xed-band graphic equalizer or parametric equalizer to a
predetermined frequency response.
Equalization can be achieved in softWare as Well as in
equalization may be applied to the data as part of the decoding
process or in a separate step. Thus, the process of equaliza
tion, either using a ?xed-bandWidth graphic equalizer or a
variable-bandWidth parametric equalizer, can be achieved in
speaker/room acoustics is largely determined by the com
plexity of the run-time equalization. For many loW- to mid
level systems, the run-time equalization is simply the para
metric or graphic equalizer already present in the softWare,
and thus correction possibilities may be limited. Thus, it
provide a more sophisticated and correct equalization to the
frequency spectrum With the same number or even feWer
back of a digital audio stream from a DVD, CD, or other audio
source. Such audio processor softWare may include an exist
ing equalization algorithm, Which may receive an input based
Thus, each band-pass ?lter in the equalizer may be adjusted
of narroW-band elements in the parametric equalizer. Large
algorithms are knoWn in the art and may be licensed from
limited granularity of the underlying equalizer. For run-time
equalizers With a limited range of center frequencies (either a
graphic equalizer or a limited-implementation of a parametric
equalizer), it may not be possible to exactly “center” on the
peak or valley in system response. Thus, more or less of the
65
frequency response is affected as desired. If a —3 dB attenu
performed by the user When installing the system and/or prior
ation is applied to a 3 dB peak, but due to the limitations of the
to listening to music and/or Watching a video or the like. An
system, applied at a frequency slightly aWay from this peak,
US 7,664,276 B2
5
6
adjacent frequencies may be unnecessarily attenuated, and
the desired “peak” not properly ?attened.
system response. This initial adjustment of equalization may
tend to ?atten most of the peaks and valleys to produce the
The second problem can be at least partially offset using a
brute force approach. If the equalization softWare Was pro
this inexact application of equalization corrections may intro
vided With an enormous number of narroW-band parametric
duce other artifacts into the system response and/or may not
equalization elements, then individual peaks and valleys
suf?ciently normalize equalization.
desired uniform linear response. HoWever, as noted above,
could be selectively eliminated in the system response. HoW
A second pass is then performed to measure the system
ever, such an approach may be processor-, memory-, and
hardWare-intensive.
response using the neW equalization settings. The neW peaks
and valleys are measured, and the equalization adjusted to try
to further ?atten response. Any number of subsequent passes
may be made to further normalize the equalization. HoWever,
in practice, the number of passes may be limited to reduce the
amount of time needed for the equalization process.
The ?rst problem canbe resolved by using an equalizer that
targets both magnitude and phase, if the system designer is
not limited to the use of an existing magnitude-only equal
ization algorithm already present in a product.
US. Pat. No. 6,721,426 to Allred et al. discloses an auto
The optimal number of iterations may be a tradeoff
betWeen test time and accuracy. For the most accurate results,
one equalizer band per pass may be adjusted, so the number of
iterations Would be at least the number of equalization bands
in the system. HoWever, such a technique may take an exces
sive amount of time. In the preferred embodiment, tWo or
matic loudspeaker equalizer. First digital data is provided for
a tolerance range for a target response curve of sound level
versus frequency for the loudspeaker. Second digital data is
generated for an actual response curve of sound level versus
frequency for the loudspeaker. The ?rst digital data is com
pared With the second digital data, and it is determined
20
Whether the actual response curve is Within the tolerance
range. If the actual response curve is not Within the tolerance
of total equalization bands in the equalizer divided by the
range, digital audio ?lters are iteratively generated, and the
digital audio ?lters are applied to the second digital data to
generate third digital data for a compensated response curve.
bands set perpass. Thus, for example, With a nine-band equal
izer, setting three bands per pass yields three passes.
25
The frequency, amplitude and bandWidth of the digital audio
?lters are automatically optimized until the compensated
BRIEF DESCRIPTION OF THE DRAWINGS
response curve is Within the tolerance range or a predeter
mined limit on the number of digital audio ?lters has been
reached, Whichever occurs ?rst.
three (or more) equalization bands are adjusted at the same
time With each pas sithe number of passes equals the number
FIG. 1 is a block diagram of the home theater surround
30
The iterative approach of Allred improves equalization of
sound speaker system in accordance With the Prior Art.
FIG. 2 is a simpli?ed block diagram of the equalization
system of the present invention.
the audio system, resulting in a ?atter system response. HoW
FIG. 3 is a graph illustrating initial system response before
ever, the iterative approach can take considerable time to
equalization correction is applied identifying peaks and val
achieve. In particular, in the system ofAllred, only one equal
Will take at least as many iterations as equalization elements
leys in the system response.
FIG. 4 is a graph illustrating initial system response, iden
to properly adjust all equalization elements and insure each
tifying peaks for equalization adjustment and illustrating
equalization adjustment does not introduce neW artifacts into
the equalization. For a consumer electronic system (e.g.,
Home Theater system), this solution may not be acceptable,
application of a proximity range to determine Which peaks
and valleys Will be equalized in a ?rst pass.
FIG. 5 is a graph illustrating system response after a ?rst
ization element is adjusted With each iteration. As a result, it
35
40
pass of equalization adjustment is applied.
as the process may continue on for some time. The consumer
may get impatient or believe the process if not functioning
FIG. 6 is a graph illustrating system response after a second
properly and terminate the process prior to completion.
pass of equalization adjustment is applied.
Thus, it remains a requirement in the art to provide an
equalization technique that more accurately equalizes a home
45
theater or other audio system While using a limited number of
applied.
equalization elements and/or Working Within the parameters
of an existing equalization algorithm. It remains a further
requirement in the art to provide an equalization technique
that optimizes the use of equalization elements for a given
DETAILED DESCRIPTION OF THE INVENTION
50
FIG. 2 is a simpli?ed block diagram of the equalization
system of the present invention. The apparatus of FIG. 2 may
audio environment. It remains a further requirement in the art
to provide an equalization technique that can optimize equal
ization settings Without requiring a large number of iterative
55
be incorporated into a Home Theater system such as that
illustrated in FIG. 1, or an other type of audio system, includ
ing but not limited to a commercial audio systems, car audio
systems, home stereo systems, and the like. For the sake of
clarity, various elements that are not essential to the under
standing of the invention are not illustrated.
60
receive data from a digital signal source and decode the data
time-consuming processes.
SUMMARY OF THE INVENTION
Rather than basing the entire equalization setup on only
one pass of the analysis phase, multiple passes are executed in
the equalization setup and modi?cation of the equalization is
performed after each pass of the analysis phase. This modi
Referring to FIG. 2, a digital signal decoder 260 may
accordingly. Examples of such decoders, as noted above,
?cation alloWs the softWare to modify its initial settings to
include DolbyTM DigitalTM AC-3 decoders, Digital Theater
Systems (DTS) decoders, Pulse Code Modulation (PCM)
decoders, and the like. Other types of decoders, including
compensate for the unexpected effects of the original equal
ization. The number of passes can vary Widely, as can the
equalization adjustment or setting at each step.
After an initial pass, the equalization is adjusted, as in the
Prior Art, based upon the location of peaks and valleys in the
FIG. 7 is a graph illustrating hoW artifacts can be intro
duced into the system response if the proximity range is not
65
proprietary decoding systems, may also be used. Decoder 260
receives digital data from a digital signal source. For ordinary
playback of audio, this digital sound source may include
US 7,664,276 B2
7
8
digital signal source 215 which may include a CD, DVD,
HDTV digital audio track, digital radio, MP-3 data stream, or
LCD display or the like so that the consumer can better
understand the process and view the results of the setup and
other digital audio data.
For setup and testing purposes, a digital testing signal 205
calibration procedure.
may be used to generate a sound pattern for various testing
FIGS. 3-5, the system response may be analyzed by the sys
As will be discussed in more detail in connection with
tem to determine which frequencies should be attenuated and
and setup purposes. As set forth in co-pending applications
Ser. Nos. 11/002,102 and 11/038,577 cited previously, the
test signal may comprise gated nose, a Maximum Length
Sequence (MLS) or the like. In some embodiments, almost
any source signal may be used for calibration, testing, and
which accentuated. The results of these decisions are used to
alter the equalizer coef?cients 270.
After an initial system response 290 has been determined,
setup, including digital signal source 215.
equalizer coef?cients 270 may be adjusted and the process
repeated. If individual elements of equalizer 270 are adjusted
The output of digital signal decoder 260 may be fed to
equalizer 210. As previously noted, equalizer 210 may com
prise a portion of digital signal decoder 260. Moreover, all or
part of both digital signal decoder 260 and equalizer 210 may
to properly calibrate equalizer 270. Moreover, if the number
of processes is limited (due to testing time considerations),
the resulting calibration may not be optimal. Thus, for
one at a time, it may take a large number of repeated processes
example, if there are seven elements in equalizer 270, and
seven processes are repeated, one for each equalizer element,
then each element is adjusted only once.
comprise software or ?rmware components of the system, as
opposed to dedicated hardware components. Thus, equalizer
210 may comprise a run-time equalizer that is executed sub
sequent to the process of digital signal decoder 260.
Equalizer 210 may be provided with equalizer coef?cients
270 to adjust the amplitude of each equalizer element. If
equalizer 210 comprises a parametric equalizer, then these
coef?cients may also include center frequency and frequency
ranges for each equalizer element. When initialized, the sys
tem may default to predetermined coef?cients. These coef?
cients may be 0 coef?cients (e.g., neither amplifying or
In the present invention, a multiple number of equalizer
20
testing time may be limited, while enhancing the adjustment
of the equalizer elements. The optimal number of iterations
may be a tradeoff between test time and accuracy. In the
preferred embodiment, two or three (or more) equalization
25
values. To reduce the amount of time for calibration and
setup, the default coef?cients may be selected to represent
proper equalization for a “typical” consumer setting or other
area.
equalizer band may be initially adjusted, the results tested,
and the band adjustment then ?ne-tuned to improve the over
all system response. Additionally, in the preferred embodi
35
signal that may be ampli?ed in ampli?er 225 and then be
reproduced in the room by speaker 230.
For purposes of illustration, only one speaker 230 is shown
in FIG. 2. It will be appreciated by one of ordinary skill in the
art that other numbers of speakers may be used, including, but
not limited to left and right front speakers, center speakers,
left and right rear speakers, surround sound speakers, sub
woofers, and the like. Each speaker may be tested separately
ment a proximity range may be applied to the initial peaks to
be adjusted, such that adjacent or proximal bands of the
equalizer are not adjusted simultaneously, resulting in arti
facts in the resultant system response.
Rather than basing the entire EQ setup on only one pass of
begins, the digital testing signal 205 (or other signal) is fed to
digital signal decoder 260 and equalizer 210, which outputs a
decoded and equalized digital audio signal to digital to analog
converter (DAC) 220. DAC 220 may then output an audio
bands are adjusted at the same time with each passithe
number of passes equals the number of total equalization
bands in the equalizer divided by the bands set per pass. Thus,
for example with a nine-band equalizer, setting three bands
per pass yields three passes.
In addition, each band can be re-adjusted to compensate for
the subsequent adjustment of other adjacent bands. Thus, an
attenuating any frequency band) or some other predetermined
The system may enter an equalization setup mode auto
matically when ?rst powered up, or at the direction of the
consumer (e.g., through infrared remote control, on-screen
menu, or the like). Once the equalization calibration process
elements may be adjusted in one process, and thus the overall
40
the analysis phase, multiple analysis phases are executed with
EQ setup and modi?cation occurring after each analysis
phase. This allows the software to modify its initial settings to
compensate for unexpected effects of the original equaliza
tion. The number of passes can vary widely, as can the EQ
45
adjustment or setting at each step. For example, one extreme
might be:
or in some combination. (Tests are typically done separately,
except when testing the combination of a speaker and sub
Do (number of bands)
50
woofer)
Analyze
Microphone 240 receives the audio signal from the room.
As set forth in co-pending applications Ser. Nos. 11/002,102
Set one EQ band
While(unsatis?ed)
and 11/038,577 cited previously, microphone 240 might also
be used for other testing purposes, such as measuring speaker
location and determining time delay. Thus, the same compo
Analyze
55
}
nents in the system may be used for more than one purpose in
I‘
setting up the system.
The output of microphone 240 may be fed to Analog to
Digital Converter (ADC) 250 that in turn outputs a digital
60
audio signal to frequency analyzer 280. Frequency analyzer
280 may process the digital audio signal from ADC 250
and/ or compare this signal with the source digital audio signal
output from equalizer 210. The result of this analysis is output
as the system response 290. System response 290 may be kept
internal to the system; however, in some embodiments, sys
tem response 290 may be displayed on an on-screen display,
At the other extreme:
Analyze
Set all EQ bands
Analyze
Tweak all EQ bands
65
Or
Analyze
Set half the EQ bands
Tweak EQ band
US 7,664,276 B2
10
Analyze
of the proximity range is to prevent one equaliZation adjust
ment from altering or affecting an adjacent equaliZation
Set the other half
Additionally, When setting a plurality of bands at one time,
adjustment.
In a subsequent cycle, peak 450 may be used to adjust
another equaliZer band to eliminate this peak. In each subse
quent cycle, one or more equaliZer elements may be adjusted
until all the equaliZer bands are optimiZed for the best system
it may be bene?cial to ensure that those bands are orthogonal
so that they do not affect each other. FIG. 3 is a graph illus
trating an example of initial system response before equal
iZation correction is applied. The X-axis represents fre
response (e. g., ?at response or some other desirable
quency, on a logarithmic scale, While the Y-axis represents
response). In an alternative embodiment, the process may be
relative amplitude in dB. As previously discussed, an ideal
system response may comprise a ?at line at the 0 dB level,
repeated to ?ne-tune the equaliZer band elements to provide
indicating that each frequency in the spectrum is reproduced
different frequencies, representing frequencies that are overly
FIG. 5 is a graph illustrating system response after equal
iZation is applied. As illustrated in FIG. 5, peaks 430 and 480
have been largely attenuated, such that the overall system
response is closer to the desirable ?at response (in this
example). Peak 450 and valleys 470 and 490 may be corrected
in a subsequent cycle, provided they are not Within the des
ampli?ed. Several valleys are illustrated that represent fre
quencies that are overly attenuated. In this example, major
ignated proximity range of one another. In this manner, more
than one peak or valley may be corrected per cycle, Without
an even better overall system response.
faithfully and at the same level relative to all other frequencies
in the spectrum.
As illustrated in the example system response of FIG. 3, the
overall response is anything but “?at”. Several peaks occur at
peaks 430, 450 and 480 are located at approximately 100 HZ,
20
and 490 are present at approximately 600 HZ and 4000 HZ,
pass of equaliZation adjustment is applied. In this example,
respectively. The rest of the spectrum is relatively ?at, or
outside the range of human hearing or system (particularly
speaker) range.
after peaks 430 and 480 have been attenuated in a ?rst round
25
iZer coe?icients. Valleys 470 and 490 are left for a subsequent
peak Width measurement as Well as the proximity range
adjustment cycle or cycles.
applied in the present invention. In this example, When setting
at a particular predetermined dB cutoff level such as —3 dB
from the peak, or by the Width at a particular percentage of the
FIG. 7 is a graph illustrating hoW artifacts can be intro
duced into the system response if the proximity range is not
applied. In FIG. 5, the neW extent of peak 450 after the ?rst
pass of equaliZation has been applied is illustrated. In FIGS.
3 and 4, this peak is higher. If the proximity range Were not
35
valley is created, and the system Will have to be “tWeaked”
40
further to eliminate this artifact.
While the present invention may be implemented in a num
ber of embodiments, a number of fundamental features are
present in one or more of these embodiments. Adjusting
multiple equaliZer bands during one process cycle is one
45
feature of the present invention. In addition, the use of the
proximity range to determine Which frequency ranges, Which
may be adjusted in one cycle Without causing adjacent equal
As second peak 450 is Within the 4x range lines 410 and
50
iZer band interference, is another feature. The use of multiple
cycles of the calibration process to ?ne-tune the equaliZer
coef?cients is yet another feature of the present invention.
There are other features of the present invention that may be
used alone or in combination With any of the aforementioned
may target one of the smaller valleys 470, 490 or the peak 480.
The use of the 4x proximity range prevents the adjustment of
adjacent equaliZer bands from interfering With each other and
producing unexpected or undesirable results. Using this tech
applied in the ?rst cycle of adjustment, and the system
attempted to adjust equaliZer coef?cients 270 for the tWo
adjacent peaks 430 and 450, the net effect Would be to over
attenuate peak 450, resulting in a neW valley 750. Thus, a neW
peak (in this example 70%, or 4 dB).
460, for the ?rst adjustment of equaliZer coef?cients 270,
peak 450 Will be ignored. Instead, the second equaliZer band
of adjustment of equaliZation coe?icients, a second round of
testing and adjustment may be performed. In this example,
only peak 450 is eliminated though adjustment of the equal
FIG. 4 is a graph illustrating initial system response, iden
tifying peaks for equaliZation adjustment and illustrating
tWo bands betWeen analysis phases, the ?rst can be anyWhere
in the spectrum, but the second should be limited to anyWhere
in the spectrum except Within a speci?ed distance of the
center frequency of the ?rst, in order to prevent interference
betWeen the tWo corrections. Given the spectrum in FIGS. 3
and 4, the ?rst large peak 430 may be targeted at 100 HZ With
the ?rst equaliZer band, but selection for the second band
Would ignore the next peak 450 at 150 HZ because of its
“close” proximity to the 100 HZ peak 430.
In this embodiment, a predetermined proximity range may
be selected, for example, as four times (4x) the bandWidth of
the ?rst peak 430. This range is represented in FIG. 4 by solid
lines 410 and 460. The bandWidth of the ?rst peak 430 is
illustrated by solid lines 420 and 440. BandWidth of a peak,
such as peak 430, may be determined by the Width of the peak
the corrections interfering With each other or otherWise cre
ating neW artifacts in the system response.
FIG. 6 is a graph illustrating system response after a second
150 HZ, and 1500 HZ, respectively. Signi?cant valleys 470
55
nique, each equaliZer element can be adjusted once and still
provide a reasonable equalization. Since more than one
features of the present invention.
Note that multiple proximity ranges can be applied in each
pass. Thus, in the example of FIG. 4, a second proximity
range could be applied to peak 480. This second proximity
range, may, for example, indicate that valleys 470 and 490 are
equaliZation element is adjusted during each stage, the overall
not to be compensated in this pass, as they are Within 4x the
numbers of cycles in the process is reduced.
In this example, a 4x proximity range is utiliZed. HoWever,
other ranges may be used Within the spirit and scope of the
present invention. For example, the proximity range may be
selected as a logarithmic scale based upon peak (or valley)
center frequency. Altemately, a ?xed proximity range or
bandWidth (or other criteria) of peak 480. Thus, valleys 470
selected one of a number of ?xed proximity ranges may be
used. The proximity range can also be determined based upon
peak (or valley) amplitude or other indicia. The main feature
60
and 490 Would not be corrected until a subsequent pass, as is
illustrated in the Example of FIG. 4. The number of proximity
ranges used in a given pass can vary and the Width or formula
used to determine the proximity range siZe can also be varied
as previously noted.
65
While the preferred embodiment and various alternative
embodiments of the invention have been disclosed and
described in detail herein, it may be apparent to those skilled
US 7,664,276 B2
11
12
(b) equalizing the audio test signal using an equalizer hav
in the art that various changes in form and detail may be made
ing a plurality of adjustable equalizer coe?icients,
therein Without departing from the spirit and scope thereof.
(c) receiving the audio test signal output from a speaker to
a signal detector,
(d) analyzing the received audio signal to determine system
response and detect peaks and valleys in the system
I claim:
1. A method for adjusting an equalizer, comprising:
(a) generating an audio test signal,
(b) equalizing the audio test signal using an equalizer hav
response; and
(e) adjusting one or more of the plurality of adjustable
ing a plurality of adjustable equalizer coef?cients,
(c) receiving the audio test signal output from a speaker to
a signal detector,
(d) analyzing the received audio signal to determine system
response and detect peaks and valleys in the system
equalizer coef?cients of the equalizer corresponding to
one or more corresponding peaks and valleys in the
system response,
repeating steps (a) through (f) to remove artifacts created in
response;
the system response due to a previous adjustment of the
(e) adjusting one or more of the plurality of adjustable
equalizer coef?cients.
equalizer coe?icients of the equalizer corresponding to
one or more corresponding peaks and valleys in the
15
system response;
performed in a digital signal decoder, the method further
repeating steps (a)-(d) using the equalizer coef?cients
adjusted in step (e), and
adjusting remaining equalizer coe?icients corresponding
to corresponding peaks or valleys in the system
includes:
20
performed in a digital signal decoder, the method further
25
signal;
an equalizer having a plurality of adjustable equalizer coef
?cients for equalizing the audio test signal;
outputting the audio test signal to a room through a speaker,
and
ing a plurality of adjustable equalizer coef?cients,
(c) receiving the audio test signal output from a speaker to
a signal detector,
(d) analyzing the received audio signal to determine system
response and detect peaks and valleys in the system
response; and
(e) adjusting one or more of the plurality of adjustable
30
adjusting one or more of the plurality of adjustable
35
system response,
Wherein the analyzer analyzes a subsequent test signal
equalized by the equalizer using adjusted equalizer coef
40
in the system response.
8. The audio equalizer of claim 7, Wherein the audio test
45
system response comprises:
50
(g) applying a proximity range to the ?rst peak or valley,
(h) discarding a subsequent peak or valley Within the prox
imity range, and repeating steps (f) through (h) for a next
peak or valley outside the proximity range.
4. The method of claim 3, Wherein the audio test signal
comprises a digital audio test signal, and the equalization is
performed in a digital signal decoder, the method further
outputting the audio test signal to a room through a speaker,
and
converting the audio test signal from the signal detector
into a digital audio signal.
5. A method for adjusting an equalizer, comprising:
(a) generating an audio test signal,
speaker, and the audio test signal from the signal detec
tor is converted into a digital audio signal before being
fed to the analyzer.
9. The audio equalizer of claim 8, Wherein the audio test
signal comprises a digital audio test signal, and the equalizer
comprises a portion of a digital signal decoder,
Wherein the digital audio test signal is converted to an
analog audio test signal, and output to a room through a
speaker, and the audio test signal from the signal detec
tor is converted into a digital audio signal before being
fed to the analyzer.
includes:
converting the digital audio test signal to an analog audio
test signal, and
signal comprises a digital audio test signal, and the equalizer
comprises a portion of a digital signal decoder,
Wherein the digital audio test signal is converted to an
analog audio test signal, and output to a room through a
equalizer coe?icients of the equalizer corresponding to
valley,
?cients and adjusts remaining equalizer coef?cients cor
responding to remaining corresponding peaks or valleys
one or more corresponding peaks and valleys in the
(i) adjusting an equalizer corresponding to a ?rst peak or
equalizer coef?cients of the equalizer corresponding to
one or more corresponding peaks and valleys in the
equalizer coe?icients of the equalizer corresponding to
system response,
an analyzer, coupled to receive the audio test signal as
output from a speaker to a signal detector, for analyzing
the received audio signal to determine system response
and detect peaks and valleys in the system response, and
one or more corresponding peaks and valleys in the
Wherein adjusting one or more of the plurality of adjustable
converting the audio test signal from the signal detector
into a digital audio signal.
7. An audio equalizer, comprising:
an audio test signal generator for generating an audio test
converting the digital audio test signal to an analog audio
test signal, and
converting the audio test signal from the signal detector
into a digital audio signal.
3. A method of adjusting an equalizer, comprising:
(a) generating an audio test signal,
(b) equalizing the audio test signal using an equalizer hav
converting the digital audio test signal to an analog audio
test signal, and
outputting the audio test signal to a room through a speaker,
and
response.
2. The method of claim 1, Wherein the audio test signal
comprises a digital audio test signal, and the equalization is
includes:
6. The method of claim 5, Wherein the audio test signal
comprises a digital audio test signal, and the equalization is
10. An audio equalizer, comprising:
60
an audio test signal generator for generating an audio test
signal;
an equalizer having a plurality of adjustable equalizer coef
?cients for equalizing the audio test signal;
an analyzer, coupled to receive the audio test signal output
from a speaker to a signal detector, for analyzing the
received audio signal to determine system response and
detect peaks and valleys in the system response, and
US 7,664,276 B2
14
13
speaker, and the audio test signal from the signal detec
tor is converted into a digital audio signal before being
fed to the analyzer.
15. A home theater, comprising:
adjusting one or more of the plurality of adjustable
equalizer coef?cients of the equalizer corresponding to
one or more corresponding peaks and valleys in the
system response,
Wherein the analyzer adjusts an equalizer coef?cient cor
responding to a ?rst peak or valley, applies a proximity
range to the ?rst peak or valley, discards subsequent
an audio test signal generator for generating an audio test
signal;
an equalizer having a plurality of adjustable equalizer coef
?cients for equalizing the audio test signal;
peaks or valleys Within the proximity range, and adjusts
at least one speaker, placed in a room, for generating sound
from the audio test signal;
at least one signal detector, placed in the room, for receiv
an equalizer coe?icient for a next peak or valley outside
the proximity range.
11. An audio equalizer, comprising:
ing sound from the speaker; and
an audio test signal generator for generating an audio test
an analyzer, coupled to receive the audio test signal as
signal;
output from the speaker to the signal detector, for ana
lyzing the received audio signal to determine system
response and detect peaks and valleys in the system
an equalizer having a plurality of adj ustable equalizer coef
?cients for equalizing the audio test signal;
an analyzer, coupled to receive the audio test signal as
output from a speaker to a signal detector, for analyzing
the received audio signal to determine system response
and detect peaks and valleys in the system response, and
response, and adjusting one or more of the plurality of
adjustable equalizer coef?cients of the equalizer corre
sponding to one or more corresponding peaks and val
20
adjusting one or more of the plurality of adjustable
Wherein the analyzer adjusts an equalizer coe?icient cor
responding to a ?rst peak or valley, applies a proximity
range to the ?rst peak or valley, discards subsequent
equalizer coef?cients of the equalizer corresponding to
one or more corresponding peaks and valleys in the
system response,
Wherein the analyzer analyzes a subsequent test signal
peaks or valleys Within the proximity range, and adjusts
25
equalized by the equalizer using adjusted equalizer coef
1 6. The home theater system of claim 15, Wherein the audio
test signal comprises a digital audio test signal, and the equal
izer comprises a portion of a digital signal decoder,
adjustment of the equalizer coe?icients.
30
signal comprises a digital audio test signal, and the equalizer
comprises a portion of a digital signal decoder,
an audio test signal generator for generating an audio test
signal;
35
signal;
an equalizer having a plurality of adjustable equalizer coef
?cients for equalizing the audio test signal;
40
at least one speaker, placed in a room, for generating sound
from the audio test signal;
at least one signal detector, placed in the room, for receiv
ing sound from the speaker; and
at least one speaker, placed in a room for generating sound
an analyzer, coupled to receive the audio test signal as
45
ing sound from the speaker; and
output from the speaker to the signal detector, for ana
lyzing the received audio signal to determine system
response and detect peaks and valleys in the system
response, and adjusting one or more of the plurality of
an analyzer, coupled to receive the audio test signal as
output from the speaker to the signal detector, for ana
lyzing the received audio signal to determine system
response and detect peaks and valleys in the system
tor is converted into a digital audio signal before being
fed to the analyzer.
17. A home theater system, comprising:
an audio test signal generator for generating an audio test
an equalizer having a plurality of adj ustable equalizer coef
?cients for equalizing the audio test signal;
from the audio test signal;
at least one signal detector, placed in the room, for receiv
Wherein the digital audio test signal is converted to an
analog audio test signal, and output to a room through a
speaker, and the audio test signal from the signal detec
Wherein the digital audio test signal is converted to an
analog audio test signal, and output to a room through a
speaker, and the audio test signal from the signal detec
tor is converted into a digital audio signal before being
fed to the analyzer.
13. A home theater system, comprising:
an equalizer coe?icient for a next peak or valley outside
the proximity range.
?cients and adjusts equalizer coef?cients to remove arti
facts created in the system response due to a previous
12. The audio equalizer of claim 11, Wherein the audio test
leys in the system response,
adjustable equalizer coef?cients of the equalizer corre
50
sponding to one or more corresponding peaks and val
leys in the system response,
Wherein the analyzer analyzes a subsequent test signal
response, and adjusting one or more of the plurality of
adjustable equalizer coef?cients of the equalizer corre
equalized by the equalizer using adjusted equalizer coef
sponding to one or more corresponding peaks and val
?cients and adjusts equalizer coef?cients to remove arti
facts created in the system response due to a previous
leys in the system response,
Wherein the analyzer analyzes a subsequent test signal
adjustment of the equalizer coef?cients.
18. The home theater system of claim 17, Wherein the audio
equalized by the equalizer using adjusted equalizer coef
test signal comprises a digital audio test signal, and the equal
izer comprises a portion of a digital signal decoder,
?cients and adjusts remaining equalizer coef?cients cor
responding to remaining corresponding peaks or valleys
in the system response.
14. The home theater system of claim 13, Wherein the audio
test signal comprises a digital audio test signal, and the equal
izer comprises a portion of a digital signal decoder,
Wherein the digital audio test signal is converted to an
analog audio test signal, and output to a room through a
60
Wherein the digital audio test signal is converted to an
analog audio test signal, and output to a room through a
speaker, and the audio test signal from the signal detec
tor is converted into a digital audio signal before being
fed to the analyzer.
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