) ADC
US 20060062405A1
(19) United States
(12) Patent Application Publication (10) Pub. N0.: US 2006/0062405 A1
McKee Cooper
(54)
(43) Pub. Date:
MULTIPASS PARAMETRIC OR GRAPHIC
Mar. 23, 2006
Publication Classi?cation
EQ FITTING
(76)
Inventor: Joel C. McKee Cooper, Lafayette, CO
(52)
(Us)
Filed:
modi?cation of the equalization is performed after each pass
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
equalization corrections may introduce other artifacts into
the system response and/or may not suf?ciently normalize
11/057,367
Feb. 15, 2005
Related U.S. Application Data
(63) Continuation-in-part of application No. 11/002,102,
?led on Dec. 3, 2004.
Continuation-in-part of application No. 11/038,577,
?led on Jan. 21, 2005.
(60)
Provisional application No. 60/612,474, ?led on Sep.
23, 2004.
Digital
Digital
Signal Source
CD, DVD, HDTV,
Testing
Signal
etc.
ABSTRACT
Multiple passes are executed in the setup of an equalizer, and
8033 Washington Road
Alexandria, VA 22308 (US)
(21) Appl. No.:
(2006.01)
(2006.01)
U.S. c1. ....................................... .. 381/103; 333/28 R
(57)
Correspondence Address:
Robert P. Bell
(22)
(51) Int. Cl.
H036 5/00
H04B 3/14
215
equalization. Asecond pass is then performed to measure the
system response using the neW equalization settings. The
neW peaks and valleys are measured, and the equalization
adjusted to try to ?atten response further. Aproximity range
may be applied to each pass, to reduce the likelihood that
adjustment of one equalizer coef?cient Will create artifacts
in the resulting system response.
205
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Signal
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210
220
Equalizer
230
240
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250
ADC
225
l
Equalizer
Coefficients
270
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Frequency
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System Response
p290
Patent Application Publication Mar. 23, 2006 Sheet 1 0f 5
US 2006/0062405 A1
[-18
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BASS SPEAKER
INTERCONNECT P——'_J
MODULE
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LEFT
SATELLITE
SPEAKER
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3°
28
/26
, REAR AMBIENCE
SPEAKER
Figure 1 (Prior Art)
24
/
RIGHT
SATELLITE
SPEAKER
Patent Application Publication Mar. 23, 2006 Sheet 2 0f 5
4
Digital
Digital
Signal Source
Testing
co, DVD, HDTV,
Signal
etc-
215
US 2006/0062405 A1
205
1
Digital
S|gnal
Decoder
l
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220
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230
240
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// 250
ADC
225
2so\
Equalizer
Frequency
Coefficients
Analyzer
‘—
270
i
System Response
F290
Figure 2
Patent Application Publication Mar. 23, 2006 Sheet 3 0f 5
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Mar. 23, 2006
US 2006/0062405 A1
MULTIPASS PARAMETRIC OR GRAPHIC EQ
FITTING
CROSS-REFERENCE TO RELATED
APPLICATIONS
[0001] The present application claims priority from Pro
visional US. Patent Application No. 60/612,474 ?led on
Sep. 23, 2004 (Cirrus Logic Docket No. 1537-DSP), and
incorporated herein by reference. The present application is
also a Continuation-In-Part of US. patent application Ser.
No. 11/002,102 entitled “TECHNIQUE FOR SUB
WOOFER DISTANCE MEASUREMENT”, ?led on Dec. 3,
2004 (Cirrus Logic Docket No. 1538-DSP), and incorpo
rated herein by reference. The present application is also a
Continuation-In-Part of US. patent application Ser. No.
11/038,577, ?led on Jan. 21, 2005 (Cirrus Logic Docket No.
1539-DSP), and incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a method and
apparatus for automatically equalizing a home theater or
other audio system. In particular, the present invention is
directed toWard a technique for providing continuous or
active adaptation of the equalization of a home theater or
other audio system.
BACKGROUND OF THE INVENTION
[0003]
Home theater systems, Which once Were expensive
luxury items, are noW becoming commonplace entertain
ment devices. Complete Home Theater systems, knoWn as a
Home Theater In a Box (HTIB), are available to consumers
at reasonable prices. HoWever, properly setting up such
Home Theater systems can sometimes be problematic for
the consumer.
Interconnect module 14 receives the audio signals from
television 12 and assembles the component left and right
channel signals for selective distribution to particular com
ponent speakers of the surround sound system 10.
[0007] The component speakers typically include a sub
Woofer 18, Which receives full range left and right signals,
but only reproduces the loW frequency components of the
audio signal. 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 signal and reproduces the (L+R) summation
signal. Preferably, front center speaker 20 is located in
proximity to television 12 and projects the acoustic output of
the (L+R) summation signal toWard the listener 28.
[0008] Interconnect module 14 also outputs the left chan
nel signal to left satellite speaker 22 and right channel signal
to right satellite speaker 24. Left satellite speaker 22 and
right satellite speaker 24 may be relatively small speakers
and need only reproduce mid range and/or high frequency
signals. Left and right satellite speakers are preferably
oriented so that the primary axis of radiation of the speaker
points upWard along a vertical axis; hoWever, other orien
tations of the satellite speakers may also provide satisfactory
performance. Interconnect module 14 also outputs an audio
signal to rear ambience speaker 26. Rear ambience speaker
26 typically receives 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 appar
ent throughout this detailed description, several embodi
ments of the invention described herein enable interconnect
module 14 to generate a variety of signals to be output to left
satellite speaker 22, right satellite speaker 24, and/or rear
ambience speaker 26. It should be noted at the outset that the
term speaker refers to a system for converting electrical
input signals to acoustic output signals Where the system
may include one or a number of crossover netWorks and/or
[0004] Home theater systems provide a number of com
ponents, 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 theater system is described, for example, in US. Pat.
No. 5 930,370, issued Jul. 27, 1999 to RuZicka, incorporated
herein by reference.
[0005] FIG. 1 depicts a diagrammatic vieW of the home
theater surround sound speaker system (the surround sound
system) 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 television (“TV”) set 12. The stereo audio source
may be any of a number of audio signal sources. It should,
thus, be noted that 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.
[0006]
transducers.
[0009] The components described in FIG. 1 typically are
arranged to optimiZe the surround sound effect to enhance
the listening experience of the vieWer 28. The vieWer 28
typically faces television 12 Which has front center speaker
20 arranged in proximity to television 12 so that center
speaker 20 and television 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, both satellite speakers typically
being located nominally midWay 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.
[0010] One problem With these home theater systems is in
adjusting the equaliZation of the system to compensate for
room acoustics, speaker type, and other factors. Tradition
ally, a consumer adjusted equaliZation using a so-called
graphic equaliZer, Where a number of narroW band-pass
Television 12 outputs an ampli?ed audio signal to
?lters are provided, each With a corresponding slide sWitch.
interconnect module 14 via a multi-conductor cable 16.
The consumer adjusts each slide sWitch to attenuate or
Multi-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.
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.
Mar. 23, 2006
US 2006/0062405 A1
[0011] The purpose of an equalizer is to provide an audio
response that is generally “?at” across the entire frequency
iZer or a variable-bandWidth parametric equaliZer, can be
spectrum. Due to limitations in system and speaker design,
bination of both.
as Well as room acoustics and interaction of room acoustics
With speaker design and placement, various frequency
ranges in a system may be attenuated or accentuated, result
ing in a sound reproduction Which is not faithful to the
original recording.
[0012] A “?at” response generally refers to the resulting
frequency 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 in softWare as Well as in hardWare, or in a com
[0017] Other systems are knoWn in the art Wherein home
theater 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 provide pre-set equaliZation levels for rock
music, jaZZ, classical, rap, or for movie or DVD playback or
the like. The equaliZation takes place in softWare Within the
home theater system. These pre-set levels do not take into
account the room acoustics and provide only limited choices
achieved due to limitations of audio components and room
to the consumer. The consumer can only select the equal
acoustics. HoWever, With a graphic equaliZer, it is possible
to improve the response considerably such that the resulting
iZation setup that sounds best for the given circumstances.
The system is not optimiZed for the room acoustics, speak
ers, and other factors affecting audio playback.
sound is a more faithful reproduction of the original sound.
[0013] The problem With manually operated graphic
equaliZers is that the equaliZation is based upon the con
sumer setting the various frequency levels based upon What
the consumer hears and What the consumer thinks Will create
[0018] More recently, one of the more popular features for
home theater systems has been some form of automatic
equaliZation setup to minimiZe adverse affects of speaker/
room interactions. Most solutions, hoWever, involve a one
the proper equaliZation for the system. This manual solution
time setup performed by the user When installing the system
is a largely empirical approach, as many consumers cannot
and/or prior to listening to music and/or Watching a video or
the like. An 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.
properly isolate various frequencies “by ear” and understand
hoW to 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.
[0014] 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, Whereas Whole bands of frequencies can be
adequately adjusted using a single circuit. Proving addi
tional equaliZer ?lter elements and sWitches to solve this
problem is prohibitively expensive. The parametric equal
iZer helps solve this problem by alloWing a limited number
of equaliZer elements to adjust audio levels in a ?exible
manner. Each level adjustment may be itself adjusted to
control a different frequency range.
[0015] Thus, each band-pass ?lter in the equaliZer may be
adjusted for Width. Frequency ranges that require a ?ne
granularity of adjustment may be more precisely controlled
using a number of narroW-band elements in the parametric
equaliZer. Large frequency ranges that can be adjusted as a
group can be controlled With one single Wide-band element
in the parametric equaliZer. In this manner, the parametric
equaliZer can provide a more sophisticated and correct
equaliZation to the frequency spectrum With the same num
ber or even feWer control elements than a typical prior art
[0019] These prior art automatic equaliZation setup sys
tems typically have three phases. First, the system is ana
lyZed 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 equaliZa
tion refers to the process of equaliZing the audio signal
during the digital decoding stage. Third, the saved settings
are used by the equaliZer at run-time as an additional
post-processing step to Whatever other audio processor
softWare is running at the time.
[0020]
Examples of such other audio processor softWare
include DolbyTM DigitalTM AC-3, Digital Theater Systems
(DTS), Pulse Code Modulation (PCM), bass management,
delay control or the like. These various digital audio pro
cessing algorithms are knoWn in the art and may be licensed
from 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
playback of a digital audio stream from a DVD, CD, or other
audio source. Such audio processor softWare may include an
existing equaliZation algorithm, Which may receive an input
based upon system response in the room.
?xed-frequency element graphic equaliZer. Again, hoWever,
[0021]
if a consumer attempts to manually control equaliZation, the
the speaker/room acoustics is largely determined by the
results are often less than optimal, as the results are based
upon the ability of the consumer to discern different fre
quency ranges.
complexity of the run-time equaliZation. For many loW- to
mid-level systems, the run-time equaliZation is simply the
parametric or graphic equaliZer already present in the soft
Ware, and thus correction possibilities may be limited. Thus,
[0016]
EqualiZation can be achieved in softWare as Well as
in hardWare. For example, When decoding a digital data
stream, such as from a CD, DVD, or other digital audio
source, equaliZation may be applied to the data as part of the
decoding process or in a separate step. Thus, the process of
equaliZation, either using a ?xed-bandWidth graphic equal
The extent to Which the system can be corrected for
it remains a dif?culty in the prior art as to hoW to best ?t a
?xed-band graphic equaliZer or parametric equaliZer to a
predetermined frequency response.
[0022] There are a number of prior solutions to the prob
lem of ?tting a ?xed-band equaliZer to a predetermined
Mar. 23, 2006
US 2006/0062405 A1
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 frequency range is too high, it may be attenu
ated, and if a particular frequency range is too loW, it may
be boosted.
[0023]
There are at least tWo problems With the curve
?tting technique. Quite often the peaks found in a system
response (here, the term “system response” refers to the
response of the speaker and room) are at least partially due
to phase-response 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.
[0029] The iterative approach of Allred improves equal
iZation of the audio system, resulting in a ?atter system
response. HoWever, the iterative approach can take consid
erable time to achieve. In particular, in the system of Allred,
only one equaliZation element is adjusted With each itera
tion. As a result, it Will take at least as many iterations as
equaliZation elements to properly adjust all equaliZation
elements and insure each 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, as the process may continue on for
some time. The consumer may get impatient or believe the
process if not functioning properly and terminate the process
prior to completion.
[0024] The “phase response” of the speaker in the room is
[0030] Thus, it remains a requirement in the art to provide
an equaliZation technique that more accurately equaliZes a
a function of frequency and is one part of the frequency
home theater or other audio system While using a limited
response. The other part is the magnitude response (often
inaccurately called the “frequency response”), Which is the
number of equaliZation elements and/or Working Within the
parameters of an existing equaliZation algorithm. It remains
poWer level (Y-axis, usually in dB) plotted against frequency
(X-axis in HZ).
technique that optimiZes the use of equaliZation elements for
[0025] A second problem With the curve ?tting technique
is the limited granularity of the underlying equaliZer. For
run-time equaliZers With a limited range of center frequen
cies (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 frequency response is affected as desired.
If a —3 dB attenuation is applied to a 3 dB peak, but due to
the limitations of the system, applied at a frequency slightly
aWay from this peak, adjacent frequencies may be unnec
essarily attenuated, and the desired “peak” not properly
?attened.
[0026] The second problem can be at least partially offset
using a brute force approach. If the equaliZation softWare
Was provided With an enormous number of narroW-band
parametric equaliZation elements, then individual peaks and
valleys could be selectively eliminated in the system
response. HoWever, such an approach may be processor-,
memory-, and hardWare-intensive.
a further requirement in the art to provide an equaliZation
a given audio environment. It remains a further requirement
in the art to provide an equaliZation technique that can
optimiZe equaliZation settings Without requiring a large
number of iterative time-consuming processes.
SUMMARY OF THE INVENTION
[0031] 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?cation alloWs the softWare to modify its
initial settings to compensate for the unexpected effects of
the original equaliZation. The number of passes can vary
Widely, as can the equaliZation adjustment or setting at each
step.
[0032] After an initial pass, the equaliZation is adjusted, as
in the Prior Art, based upon the location of peaks and valleys
in the system response. This initial adjustment of equaliZa
system designer is not limited to the use of an existing
tion may tend to ?atten most of the peaks and valleys to
produce the desired uniform linear response. HoWever, as
noted above, this inexact application of equaliZation correc
tions may introduce other artifacts into the system response
magnitude-only equaliZation algorithm already present in a
and/or may not sufficiently normaliZe equaliZation.
[0027]
The ?rst problem can be resolved by using an
equaliZer that targets both magnitude and phase, if the
product.
[0028]
[0033]
Us. Pat. No. 6,721,426 to Allred et al. discloses an
automatic loudspeaker equaliZer. First digital data is pro
vided 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 compared With the second digital data, and it
is determined Whether the actual response curve is Within the
tolerance range. If the actual response curve is not Within the
A second pass is then performed to measure the
system 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.
[0034]
The optimal number of iterations may be a tradeoff
tolerance 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. The frequency, amplitude and bandWidth of
the digital audio ?lters are automatically optimiZed until the
betWeen test time and accuracy. For the most accurate
compensated response curve is Within the tolerance range or
a predetermined limit on the number of digital audio ?lters
has been reached, Whichever occurs ?rst.
embodiment, tWo or three (or more) equaliZation bands are
adjusted at the same time With each pass—the number of
passes equals the number of total equaliZation bands in the
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 excessive amount of time. In the preferred
Mar. 23, 2006
US 2006/0062405 A1
equalizer divided by the bands set per pass. Thus, for
example, With a nine-band equalizer, setting three bands per
pass yields three passes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] FIG. 1 is a block diagram of the home theater
surround sound speaker system in accordance With the Prior
comprise a portion of digital signal decoder 260. Moreover,
all or part of both digital signal decoder 260 and equalizer
210 may 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 subsequent to the process of digital signal
decoder 260.
[0046] Equalizer 210 may be provided With equalizer
Art.
[0036] FIG. 2 is a simpli?ed block diagram of the equal
ization system of the present invention.
[0037] FIG. 3 is a graph illustrating initial system
response before equalization correction is applied identify
ing peaks and valleys in the system response.
[0038] FIG. 4 is a graph illustrating initial system
response, identifying peaks for equalization adjustment and
illustrating application of a proximity range to determine
Which peaks and valleys Will be equalized in a ?rst pass.
[0039] FIG. 5 is a graph illustrating system response after
a ?rst pass of equalization adjustment is applied.
[0040] FIG. 6 is a graph illustrating system response after
a second pass of equalization adjustment is applied.
[0041] FIG. 7 is a graph illustrating hoW artifacts can be
introduced into the system response if the proximity range is
not applied.
DETAILED DESCRIPTION OF THE
INVENTION
[0042] FIG. 2 is a simpli?ed block diagram of the equal
ization system of the present invention. The apparatus of
FIG. 2 may be incorporated into a Home Theater system
such as that illustrated in FIG. 1, or an other type of audio
system, including 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 understanding of the invention are not
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 system may default to predetermined coef?
cients. These coef?cients may be 0 coef?cients (e.g., neither
amplifying or attenuating any frequency band) or some other
predetermined 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.
[0047] The system may enter an equalization setup mode
automatically 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 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 signal that may be ampli?ed in ampli?er 225
and then be reproduced in the room by speaker 230.
[0048] 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, subWoofers, and the like. Each speaker may be
tested separately or in some combination. (Tests are typi
cally done separately, except When testing the combination
illustrated.
of a speaker and subWoofer)
[0049] Microphone 240 receives the audio signal from the
[0043] Referring to FIG. 2, a digital signal decoder 260
room. As set forth in co-pending applications Ser. Nos.
may receive data from a digital signal source and decode the
11/002,102 and 11/038,577 cited previously, microphone
data accordingly. Examples of such decoders, as noted
240 might also be used for other testing purposes, such as
above, include DolbyTM DigitalTM AC-3 decoders, Digital
measuring speaker location and determining time delay.
Theater Systems (DTS) decoders, Pulse Code Modulation
(PCM) decoders, and the like. Other types of decoders,
including proprietary decoding systems, may also be used.
Thus, the same components in the system may be used for
more than one purpose in setting up the system.
Decoder 260 receives digital data from a digital signal
source. For ordinary playback of audio, this digital sound
source may include digital signal source 215 Which may
include a CD, DVD, HDTV digital audio track, digital radio,
MP-3 data stream, or other digital audio data.
[0044] For setup and testing purposes, a digital testing
signal 205 may be used to generate a sound pattern for
various testing 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 setup, including digital signal source
215.
[0045] The output of digital signal decoder 260 may be fed
to equalizer 210. As previously noted, equalizer 210 may
[0050] The output of microphone 240 may be fed to
Analog to Digital Converter (ADC) 250 that in turn outputs
a digital 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, system response 290 may be displayed on an
on-screen display, LCD display or the like so that the
consumer can better understand the process and vieW the
results of the setup and calibration procedure.
[0051]
As Will be discussed in more detail in connection
With FIGS. 3-5, the system response may be analyzed by the
system to determine Which frequencies should be attenuated
and Which accentuated. The results of these decisions are
used to alter the equalizer coef?cients 270.
Mar. 23, 2006
US 2006/0062405 A1
[0052]
After an initial system response 290 has been
determined, equalizer coefficients 270 may be adjusted and
the process repeated. If individual elements of equalizer 270
are adjusted one at a time, it may take a large number of
[0064] Analyze
[0065]
Set the other half
repeated processes to properly calibrate equalizer 270.
[0066] Additionally, When setting a plurality of bands at
Moreover, if the number of processes is limited (due to
one time, it may be bene?cial to ensure that those bands are
testing time considerations), the resulting calibration may
orthogonal so that they do not affect each other. FIG. 3 is a
not be optimal. Thus, for example, if there are seven
elements in equalizer 270, and seven processes are repeated,
one for each equalizer element, then each element is
graph illustrating an example of initial system response
before equalization correction is applied. The X-axis repre
adjusted only once.
represents relative amplitude in dB. As previously discussed,
[0053] In the present invention, a multiple number of
equalizer elements may be adjusted in one process, and thus
the overall testing time may be limited, While enhancing the
adjustment of the equalizer elements. The optimal number of
sents frequency, on a logarithmic scale, While the Y-axis
an ideal system response may comprise a ?at line at the 0 dB
level, indicating that each frequency in the spectrum is
reproduced faithfully and at the same level relative to all
other frequencies in the spectrum.
iterations may be a tradeoff betWeen test time and accuracy.
In the preferred embodiment, tWo or three (or more) equal
ization bands are adjusted at the same time With each
pass—the 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.
[0054]
In addition, each band can be re-adjusted to com
pensate for the subsequent adjustment of other adjacent
bands. Thus, an equalizer band may be initially adjusted, the
results tested, and the band adjustment then ?ne-tuned to
improve the overall system response. Additionally, in the
preferred embodiment 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 simulta
neously, resulting in artifacts in the resultant system
response.
[0055]
Rather than basing the entire EQ setup on only one
pass of 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 equalization. The number of passes can vary Widely,
as can the EQ adjustment or setting at each step. For
example, one extreme might be:
[0067] As illustrated in the example system response of
FIG. 3, the overall response is anything but “?at”. Several
peaks occur at different frequencies, representing frequen
cies that are overly ampli?ed. Several valleys are illustrated
that represent frequencies that are overly attenuated. In this
example, major peaks 430, 450 and 480 are located at
approximately 100 Hz, 150 Hz, and 1500 Hz, respectively.
Signi?cant valleys 470 and 490 are present at approximately
600 Hz and 4000 Hz, respectively. The rest of the spectrum
is relatively ?at, or outside the range of human hearing or
system (particularly speaker) range.
[0068] FIG. 4 is a graph illustrating initial system
response, identifying peaks for equalization adjustment and
illustrating peak Width measurement as Well as the proximity
range applied in the present invention. In this example, When
setting 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.
[0069] In this embodiment, a predetermined proximity
Do (number of bands)
{
Analyze
Set one EQ band
While(unsatis?ed)
Analyze
Tweak EQ band
}
}
[0056]
At the other extreme:
[0057] Analyze
[0058] Set all EQ bands
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 at a particular predetermined dB cutoff level such
as —3 dB from the peak, or by the Width at a particular
percentage of the peak (in this example 70%, or 4 dB).
[0070] As second peak 450 is Within the 4x range lines
410 and 460, for the ?rst adjustment of equalizer coef?cients
270, peak 450 Will be ignored. Instead, the second equalizer
band 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
[0059] Analyze
each other and producing unexpected or undesirable results.
[0060] TWeak all EQ bands
once and still provide a reasonable equalization. Since more
Using this technique, each equalizer element can be adjusted
[0061] Or
[0062] Analyze
[0063]
Set half the EQ bands
than one equalization element is adjusted during each stage,
the overall numbers of cycles in the process is reduced.
[0071] In this example, a 4x proximity range is utilized.
HoWever, other ranges may be used Within the spirit and
Mar. 23, 2006
US 2006/0062405 A1
scope of the present invention. For example, the proximity
range may be selected as a logarithmic scale based upon
proximity range could be applied to peak 480. This second
proximity range, may, for example, indicate that valleys 470
peak (or valley) center frequency. Alternately, a ?xed prox
and 490 are not to be compensated in this pass, as they are
imity range or selected one of a number of ?xed proximity
ranges may be used. The proximity range can also be
Within 4x the bandWidth (or other criteria) of peak 480.
determined based upon peak (or valley) amplitude or other
indicia. The main feature of the proximity range is to prevent
one equalization adjustment from altering or affecting an
adjacent equalization adjustment.
[0072] In a subsequent cycle, peak 450 may be used to
adjust another equaliZer band to eliminate this peak. In each
Thus, valleys 470 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 prox
imity range siZe can also be varied as previously noted.
[0078] While the preferred embodiment and various alter
adjusted until all the equaliZer bands are optimiZed for the
native embodiments of the invention have been disclosed
and described in detail herein, it may be apparent to those
skilled in the art that various changes in form and detail may
best system response (e.g., ?at response or some other
be made therein Without departing from the spirit and scope
desirable response). In an alternative embodiment, the pro
cess may be repeated to ?ne-tune the equaliZer band ele
thereof.
ments to provide an even better overall system response.
I claim:
subsequent cycle, one or more equaliZer elements may be
1. A method for adjusting an equaliZer, comprising:
[0073] FIG. 5 is a graph illustrating system response after
equaliZation 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 designated proximity range of one another. In this
manner, more than one peak or valley may be corrected per
cycle, Without the corrections interfering With each other or
otherWise creating neW artifacts in the system response.
[0074] FIG. 6 is a graph illustrating system response after
a second pass of equaliZation adjustment is applied. In this
example, after peaks 430 and 480 have been attenuated in a
?rst round of adjustment of equaliZation coefficients, a
second round of testing and adjustment may be performed.
In this example, only peak 450 is eliminated though adjust
ment of the equaliZer coef?cients. Valleys 470 and 490 are
left for a subsequent adjustment cycle or cycles.
(a) generating an audio test signal,
(b) equaliZing the audio test signal using an equaliZer
having a plurality of adjustable equaliZer coef?cients,
(c) receiving an audio test signal output from a speaker to
a signal detector,
(d) analyZing the received audio signal to determine
system response and detect any peaks and valleys in the
system response; and
(e) adjusting at least a portion of the equaliZer coefficients
of the equaliZer corresponding to at least a portion of
any corresponding peaks and valleys in the system
response.
2. The method of claim 1, further comprising:
repeating steps (a)-(d) using the equaliZer coefficients
adjusted in step (e), and
adjusting any remaining equaliZer coef?cients corre
sponding to any corresponding peaks or valleys in the
system response.
[0075] FIG. 7 is a graph illustrating hoW artifacts can be
introduced 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
3. The method of claim 1, Wherein adjusting at least a
FIGS. 3 and 4, this peak is higher. If the proximity range
Were not applied in the ?rst cycle of adjustment, and the
system attempted to adjust equaliZer coef?cients 270 for the
portion of the equaliZer coefficients of the equaliZer corre
sponding to at least a portion of any corresponding peaks
and valleys in the system response comprises:
tWo adjacent peaks 430 and 450, the net effect Would be to
over-attenuate peak 450, resulting in a neW valley 750. Thus,
(f) adjusting an equaliZer corresponding to a ?rst peak or
a neW valley is created, and the system Will have to be
“tweaked” further to eliminate this artifact.
(g) applying a proximity range to the ?rst peak or valley,
[0076] While the present invention may be implemented
(h) discarding any subsequent peak or valley Within the
proximity range, and
in a number 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 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 adja
valley,
repeating steps
through (h) for a next peak or valley
outside the proximity range.
4. The method of claim 1, further comprising:
repeating steps (a) through
to remove any artifacts
cent equaliZer band interference, is another feature. The use
of multiple cycles of the calibration process to ?ne-tune the
created in the system response due to a previous
equaliZer coef?cients is yet another feature of the present
5. The method of claim 1, Wherein the audio test signal
comprises a digital audio test signal, and the equaliZation is
adjustment of the equaliZer coef?cients.
invention. There are other features of the present invention
that may be used alone or in combination With any of the
performed in a digital signal decoder, the method further
aforementioned features of the present invention.
includes:
[0077] Note that multiple proximity ranges can be applied
in each pass. Thus, in the example of FIG. 4, a second
converting the digital audio test signal to an analog audio
test signal, and
Mar. 23, 2006
US 2006/0062405 A1
outputting the audio test signal to a room through a
speaker, and
an equaliZer having a plurality of adjustable equaliZer
coef?cients for equaliZing the audio test signal;
converting the audio test signal from the signal detector
into a digital audio signal.
6. An audio equalizer, comprising:
at least one speaker, placed in a room, for generating
sound from the audio test signal;
an audio test signal generator for generating an audio test
at least one signal detector, placed in the room, for
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 as
output from a speaker to a signal detector, for analyZing
the received audio signal to determine system response
and detect any peaks and valleys in the system
response, and adjusting at least a portion of the equal
iZer coef?cients of the equaliZer corresponding to at
least a portion of any corresponding peaks and valleys
in the system response.
7. The audio equaliZer of claim 6, Wherein the analyZer
receiving sound from the speaker; and
an analyZer, coupled to receive the audio test signal as
output from the speaker to the signal detector, for
analyZing the received audio signal to determine sys
tern response and detect any peaks and valleys in the
system response, and adjusting at least a portion of the
equaliZer coef?cients of the equaliZer corresponding to
at least a portion of any corresponding peaks and
valleys in the system response.
12. The home theater system of claim 11, Wherein the
analyZer analyZes a subsequent test signal equaliZed by the
equaliZer using adjusted equaliZer coef?cients and adjusts
analyZes a subsequent test signal equaliZed by the equaliZer
using adjusted equaliZer coefficients and adjusts any remain
ing equaliZer coef?cients corresponding to any remaining
any remaining equaliZer coef?cients corresponding to any
remaining corresponding peaks or valleys in the system
corresponding peaks or valleys in the system response.
8. The audio equaliZer of claim 6, Wherein the analyZer
adjusts an equaliZer coef?cient corresponding to a ?rst peak
13. The home theater system of claim 11, Wherein the
analyZer adjusts an equaliZer coef?cient corresponding to a
?rst peak or valley, applies a proximity range to the ?rst peak
or valley, discards any subsequent peak or valley Within the
proximity range, and adjusts an equaliZer coef?cient for a
neXt peak or valley outside the proximity range.
14. The home theater system of claim 11, Wherein the
or valley, applies a proximity range to the ?rst peak or valley,
discards any subsequent peak or valley Within the proximity
range, and adjusts an equaliZer coef?cient for a neXt peak or
valley outside the proximity range.
9. The audio equaliZer of claim 6, Wherein the analyZer
analyZes a subsequent test signal equaliZed by the equaliZer
using adjusted equaliZer coef?cients and adjusts equaliZer
coef?cients to remove any artifacts created in the system
response.
analyZer analyZes a subsequent test signal equaliZed by the
equaliZer using adjusted equaliZer coef?cients and adjusts
equaliZer coef?cients to remove any artifacts created in the
system response due to a previous adjustment of the equal
response due to a previous adjustment of the equaliZer
coef?cients.
10. The audio equaliZer of claim 6, Wherein the audio test
iZer coefficients.
15. The home theater system of claim 11, Wherein the
signal comprises a digital audio test signal, and the equaliZer
comprises a portion of a digital signal decoder, Wherein the
equaliZer comprises a portion of a digital signal decoder,
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 detector is converted into a digital
audio signal before being fed to the analyZer.
11. A home theater system, comprising:
an audio test signal generator for generating an audio test
signal;
audio test signal comprises a digital audio test signal, and the
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
detector is converted into a digital audio signal before
being fed to the analyZer.
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