Method and apparatus for removing audio artifacts

Method and apparatus for removing audio artifacts
US 20030123644A1
(19) United States
(12) Patent Application Publication (10) Pub. No.: US 2003/0123644 A1
(43) Pub. Date:
Harrow et al.
(54) METHOD AND APPARATUS FOR
Jul. 3, 2003
Publication Classi?cation
REMOVING AUDIO ARTIFACTS
(76) Inventors: Scott E. Harrow, Scottsdale, AZ (US);
(51)
Int. Cl? .
(52)
Us. 01. ...................................................... .. 379/387.01
H04M 9/00; H04M 1/00
Samuel L. Thomasson, Gilbert, AZ
(Us)
(57)
Correspondence Address:
A telephone having a line input, a line output, a handset
microphone, and a handset speaker also includes a ?rst soft
Paul F Wille
6407 E Clinton Street
This is a publication of a continued pros
mute circuit coupling the handset microphone and the line
output and a second soft mute circuit coupling the line input
and the handset speaker. The telephone is operated in a ?rst
ecution application (CPA) ?led under 37
mode and can change modes only after muting one or both
CFR 1.53(d).
soft mute circuits, changing mode, and then operating in the
second mode only after unmuting the circuits. The muting
Scottsdale, AZ 85254 (US)
(*)
Notice:
ABSTRACT
(21) Appl. No.:
09/491,360
(22) Filed:
Jan. 26, 2000
may be momentary or prolonged, depending upon the par
ticular mode of operation. An additional soft mute circuit is
used in a speakerphone.
160
Patent Application Publication
Jul. 3, 2003 Sheet 1 0f 8
US 2003/0123644 A1
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Patent Application Publication
Jul. 3, 2003 Sheet 2 0f 8
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US 2003/0123644 A1
Patent Application Publication
Jul. 3, 2003 Sheet 3 0f 8
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Patent Application Publication
Jul. 3, 2003 Sheet 5 0f 8
US 2003/0123644 A1
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NOISE r’
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Patent Application Publication
145
Jul. 3, 2003 Sheet 6 0f 8
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US 2003/0123644 A1
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FIG. 9
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UN_MUTE
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Patent Application Publication
Jul. 3, 2003 Sheet 7 0f 8
US 2003/0123644 A1
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172
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Patent Application Publication
Jul. 3, 2003 Sheet 8 0f 8
FIG. 12
US 2003/0123644 A1
Jul. 3, 2003
US 2003/0123644 A1
METHOD AND APPARATUS FOR REMOVING
AUDIO ARTIFACTS
[0011] SWitching ?lters, putting a caller on hold, activat
ing a second line, sWitching betWeen speaker phone and a
CROSS-REFERENCE TO RELATED
APPLICATIONS
signals. Above-identi?ed, co-pending application (5) dis
[0001] This application includes material disclosed in the
following applications assigned to the assignee of this
the ?lters are selected. It is desired to provide even more
hand set, and other such functions all generate transient
closes a circuit for eliminating transient signals by muting an
output before sWitching ?lters and unmuting the output after
functions and yet be unobtrusive in operation.
invention. The entire contents of each of these earlier
applications are incorporated herein by reference.
[0012] It is knoWn in the art to mute a poWer ampli?er
When the ampli?er is turned on. US. Pat. No. 4,983,927
[0002] (1) application Ser. No. 09/360,211, ?led Jul. 23,
(ToraZZina) discloses a bias circuit that causes a poWer
1999, entitled “Acoustic and Electronic Echo Cancellation”,
ampli?er to go through “mute” and “standby” states When
the ampli?er changes from normal operation to “cut-off” for
now US. Pat. No.
[0003] (2) application Ser. No. 09/413,675, ?led Oct. 6,
1999, entitled “Tagging Echoes With LoW Frequency
Noise”, now US. Pat. No.
.
[0004] (3) application Ser. No. 09/435,374, ?led Nov. 5,
1999, entitled “Background Communication using ShadoW
of Audio Signal”, now US. Pat. No.
[0005] (4) application Ser. No. 09/476,468, ?led Dec. 30,
1999, entitled “Band-by-Band Full Duplex Communica
tion”, now US. Pat. No.
[0006]
.
(5) application Ser. No. 09/
, ?led Jan. 13,
2000, entitled “Soft Mute Circuit”, now US. Pat. No.
blocking transients.
[0013] In vieW of the foregoing, it is therefore an object of
the invention to provide a method for removing all audio
artifacts from a telephone.
[0014] Another object of the invention is to provide a
telephone that changes state With no perceptible loss of
audio information.
[0015] A further object of the invention is to provide an
operating system that adapts a telephone to a variety of
possible operating conditions Without intervention by a user.
[0016]
Another object of the invention is to provide a state
machine for a telephone that is transparent to a user.
SUMMARY OF THE INVENTION
BACKGROUND
[0017] The foregoing objects are achieved in this inven
[0007] This invention relates to a method for controlling
the operation of a telephone and, in particular, to a method
for operating a telephone to remove unWanted audio arti
facts.
[0008] Advances in programmable digital logic and ?Xed
digital logic has enabled function upon function to be added
to a product, as apparent for eXample from the number of
services presently offered in addition to basic telephone
service. Within a telephone, particularly a cellular telephone,
a plurality of functions are carried out that are transparent to
a user, ie the user is unaWare of the functions taking place.
[0009] A problem With the desire and ability to add
functions Without limit is the possibility that the functions
Will interact, causing unexpected results. Another problem,
of particular concern in a telephone, is the desire to eliminate
noise. There are several kinds of noise, one of Which is an
echo, either acoustic or electrical. Another kind of noise is
a transient signal produced by sWitching electrical signals
With a telephone.
[0010] Many techniques have been developed to improve
the clarity of the sound in a telephone. One such technique
uses What is knoWn as a comb ?lter; ie a plurality of ?lters
tion in Which a telephone having a line input, a line output,
a handset microphone, and a handset speaker also includes
a ?rst soft mute circuit coupling the handset microphone and
the line output and a second soft mute circuit coupling the
line input and the handset speaker. The telephone is operated
in a ?rst mode and can change modes only after muting one
or both soft mute circuits, changing mode, and then oper
ating in the second mode only after unmuting the circuits.
The muting may be momentary or prolonged, depending
upon the particular mode of operation. An additional soft
mute circuit is used in a speakerphone.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] A more complete understanding of the invention
can be obtained by considering the folloWing detailed
description in conjunction With the accompanying draWings,
in Which:
[0019] FIG. 1 is a block diagram of a pair of telephones
having complementary comb ?lters as knoWn in the prior
art;
[0020] FIG. 2 is a chart illustrating the frequency
responses of the ?lters in FIG. 1;
Wherein band pass ?lters alternate With band stop ?lters.
Comb ?lters With complementary pass and stop bands are
coupled in the tWo audio channels connecting the tWo
stations of a telephone call. That is, the pass bands in one
channel are the stop bands in the other channel. As a result,
a signal traveling in one direction Will be slightly attenuated
but a signal traveling in a loop, ie an echo, Will encounter
both sets of stop bands and be highly attenuated. Another
attempt at reducing noise requires selecting a subset of band
[0021] FIG. 3 is a block diagram of the microphone to line
output channel in a telephone constructed in accordance
With one aspect of the invention;
pass ?lters from a larger set.
tion;
[0022]
FIG. 4 is a block diagram of the line to speaker
channel in a telephone constructed in accordance With one
aspect of the invention;
[0023] FIG. 5 is a block diagram of a soft mute circuit
constructed in accordance With another aspect of the inven
Jul. 3, 2003
US 2003/0123644 A1
[0024] FIG. 6 is a chart illustrating the operation of the
circuit in FIG. 5;
?lters in each channel and control circuitry for assigning the
?lters to each channel. The ?lters are assigned in such a Way
as to maintain full duplex operation if at all possible.
[0025] FIG. 7 is a block diagram of a plurality of soft mute
circuits in a telephone constructed in accordance With
[0036]
another aspect of the invention;
Which ?lters are allocated betWeen tWo channels in accor
[0026] FIG. 8 is a How chart illustrating the operating
system of the invention;
[0027]
FIG. 9 illustrates a poWer-on state machine con
structed in accordance With the invention;
[0028] FIG. 10 illustrates a mute sequence state machine
constructed in accordance With the invention
[0029] FIG. 11 illustrates a multiplex sequence state
machine constructed in accordance With the invention;
[0030]
FIG. 12 illustrates an A/B shadoW state machine.
DETAILED DESCRIPTION OF THE
INVENTION
[0031] FIG. 1 illustrates the operation of complementary
comb ?lters. In FIG. 1, sound incident upon microphone 11
is converted into an electrical signal and coupled to tele
phone 12. A portion of the circuitry Within telephone 12
includes band pass ?lters 13, 14, 15, 16, and 17. For a
bandWidth of 300-3,400 HZ, ?ve ?lters are typical. More
than ?ve ?lters may result in too much overlap betWeen
bands.
[0032] Telephone 12 also includes notch ?lters 21, 22, 23,
24, and 25. The center frequencies of the notch ?lters
correspond to the center frequencies of the band pass ?lters.
Thus, a signal passing through the band pass ?lters, traveling
along transmission line 27 and re?ected back to transmission
line 28 Would be attenuated by the notch ?lters. A single
telephone constructed in this fashion provides approxi
mately 10 dB of attenuation of a signal betWeen microphone
11 and speaker 29 for electronic echoes.
[0033]
Telephone 30 is constructed in like manner except
that the center frequencies of the ?lters are offset from the
center frequencies of the ?lters in telephone 12. Speci?cally,
the center frequencies of notch ?lters 31, 32, 33, 34, and 35
are betWeen the center frequencies of the band pass ?lters in
telephone 12. Thus, the notch ?lters in telephone 30 are
aligned With the dead bands betWeen the band pass ?lters in
telephone 12, Which further increases the effectiveness of the
circuit.
[0034] Telephone 30 also includes band pass ?lters 41, 42,
43, 44, and 45 having the same center frequencies as the
notch ?lters in telephone 30. Thus, a signal on input 47, e. g.,
from a microphone (not shoWn), is divided among the band
pass ?lters, summed, and transmitted over line 28 to tele
phone 12. The center frequencies of the notch ?lters in
telephone 12 correspond to the dead bands betWeen the
FIGS. 3 and 4 together illustrate a telephone in
dance With any one of several priorities. FIG. 3 is a block
diagram of a ?rst channel, extending from microphone 51 to
line output 52, and FIG. 4 is a block diagram of a second
channel, extending from line input 53 to speaker output 54.
Ahandset (not shoWn) may be included in the telephone and
coupled to the lines by appropriate sWitching circuitry.
[0037] Sound incident upon microphone 11 (FIG. 3) is
converted into an electrical signal and coupled to Weighting
?lter 56. Weighting ?lter 56 reduces the amplitude of loW
frequency signals to provide a more even energy distribution
among the bands. Filter 56 can also be used to correct for
non-linearities in the frequency response of microphone 51.
The output from ?lter 56 is coupled to a ?rst plurality of
band pass ?lters, e.g. one-third octave ?lters. Much of the
apparatus is duplicative and only one band is described.
[0038] Band pass ?lter 57 is coupled to ?lter 56 and to
amplitude detector 58, Which, for example, includes a rec
ti?er and a loW pass ?lter. More complex amplitude detec
tors can be used instead. The output from amplitude detector
58 is coupled to sample and hold circuit 59, Which provides
a stable signal for controller 61.
[0039] Weighting ?lter 63 (FIG. 4) receives signals from
line input 53 and is coupled to a second plurality of band
pass ?lters. Band pass ?lter 64 is coupled to ?lter 63 and to
amplitude detector 65. The output from amplitude detector
65 is coupled to sample and hold circuit 66. Controller 61
receives the signals from all the sample and hold circuits and
contains the logic for comparing the amplitudes of the
signals in each band in each channel. The logic can be ?xed
or programmable.
[0040] In FIG. 3, controller 61 is coupled to the control
inputs to multiplex circuit 71. Each band pass ?lter, such as
?lter 57, has an output coupled to a signal input of multiplex
circuit 71, Which has a plurality of signal output lines
coupled to summation circuit 72. The output of summation
circuit 72 is coupled to de-Weighting ?lter 73, Which as the
inverse frequency response of ?lter 56. The output of
de-Weighting ?lter 73 is coupled to line output 52.
[0041] In FIG. 4, controller 61 is coupled to the control
inputs to multiplex circuit 76. Each band pass ?lter, such as
?lter 64, has an output coupled to a signal input of multiplex
circuit 76, Which has a plurality of signal output lines
coupled to summation circuit 77. The output of summation
circuit 77 is coupled to de-Weighting ?lter 78, Which as the
inverse frequency response of ?lter 63. The output of
de-Weighting ?lter 63 is coupled to speaker output 54.
bands of band pass ?lters 41-45, enhancing the operation of
[0042] With all the data ?oWing into controller 61, the
these ?lters.
?lters can be allocated several different Ways. For example,
the loudest signal from any ?lter is found and that ?lter and
[0035] The operation of telephones 12 and 30 is illustrated
in FIG. 2. The center frequencies are numbered consistently
With FIG. 1. There are tWo sets of ?lters for tWo telephones,
Which means that one must have an “A” telephone and a “B”
the alternate ?lters in the same bank are allocated to a line.
The ?lters in the second bank that correspond to the remain
ing ?lters in the ?rst bank are assigned to the other line.
telephone in order to obtain complementary ?lter character
[0043] For example, ?lter 81 (FIG. 3) and ?lter 82 (FIG.
istics. In accordance With one aspect of the invention, this
4) have substantially the same center frequency. If ?lter 81
produces the loudest signal of all, then the output from ?lter
problem is overcome by having a plurality of band pass
Jul. 3, 2003
US 2003/0123644 A1
81 is coupled to summation circuit 72 by multiplex circuit
71. Filter 82 is cut off from summation network 77 by
multiplex circuit 76, While ?lter 83 is coupled to the sum
mation netWork. Alternate ?lters in each bank are enabled,
allocating the ten bands betWeen the tWo channels.
[0044] FIG. 5 is a schematic of a circuit that is preferably
substituted for a multiplex circuit and a summation circuit,
as used in FIGS. 3 and 4. In FIG. 5, soft mute circuit 90
includes summation circuit 91 and variable gain circuit 92.
Inputs 93, 94, 95, 96, and 97 are from separate signal sources
[not shoWn] and are selected in accordance With data on
input 102 by Way of decoder 101. In the ?gures, plural lines
are represented by a single heavy line rather than a plurality
of thin lines. Input 102 is actually ?ve inputs, one enable line
for each signal line. An advantage of having a summation
circuit shoWn is that the signal lines can be summed in any
combination on output line 103.
[0045] Circuit 92 includes a variable gain ampli?er that
adjusts the amplitude of the signal on line 103 and couples
the adjusted signal to circuit output 107. Circuit 92 is
controlled by enable input 104 and register 105. In one
embodiment of the invention, register 105 Was eight bits
Wide. The data in the register determines the maximum
amplitude of the signal on output 107.
[0046] The operation of soft mute circuit 90 is illustrated
in FIG. 6. Assuming unity (Zero dB) gain as an initial
condition, a logic “1” on enable input 104 causes the gain of
circuit 92 to decrease incrementally for as long as pin 104
remains at a logic “1” or until a minimum gain is reached,
preferably —40 dB or more.
[0047] The gain remains at minimum 111 (FIG. 6) so long
as a logic “1” is applied to input 104. Gap 112 represents the
mute period. When a logic “0” is applied to input 114, the
gain of the circuit increases to a value corresponding the data
in register 105. By reducing the gain to a minimum prior to
a transient, the transient is not coupled to output 107. Thus,
the circuit illustrated in FIG. 5 is used in several places in
a telephone constructed in accordance With the invention.
[0048] FIG. 7 is a block diagram of a portion of a
telephone constructed in accordance With one aspect of the
invention. Blocks 121, 122, and 123 are “soft mute” circuits
constructed as illustrated in FIG. 5. The output from mute
circuit 121, labeled “BRBOUT”, is coupled to the speaker
in a base receiver or speaker phone. The output from mute
circuit 122, labeled “HS13OUT”, is coupled to the speaker in
the earpiece of a handset. The output from mute circuit 123,
labeled “L13OUT”, is coupled to the line output of the
telephone.
[0049] Some inputs are common to all three mute circuits,
eg the “DTMF” tones being dialed. The “NOISE” input to
mute circuit 121 receives a noise marker signal as described
in related application (1), identi?ed above. The “NOTCH”
input is coupled to the noise reduction ?lters described
above. The “LBIN” input is coupled to the input line to the
telephone, connecting the telephone to a netWork.
[0050]
Mute circuit 122 has three inputs. The “DTMF”
and “L13IN” inputs are in common With mute circuit 121.
The “HS13MIC” input is in common With mute circuit 123
and is coupled to the microphone in the handset (not shoWn).
[0051] The “SHADOW” input to mute circuit 123
receives a shadoW signal as described in related application
(2), identi?ed above. (A shadoW signal is an audio signal
delayed less than ?fty milliseconds). Mute circuit 123 com
bines the delayed signal With an undelayed signal on input
“BRBMIC” or input “HS13MIC”. Input “BR13MIC” is
coupled to the microphone in the base receiver. Input “A/B”
is coupled to the output of another soft mute circuit that
activates ?lters in group “A” or in group “B”, depending
upon Whether or not a shadoW signal is detected; see related
application (3) identi?ed above. (In order to have comple
mentary comb ?lters, an “A” telephone must communicate
With a “B” telephone.)
[0052]
Multiplex circuit 126 provides selection data on
bus 127. Each mute control circuit decodes the data to
provide mute enable and selection signals to the respective
mute circuits. Taking mute circuit 121 as an example,
control circuit 131 receives data from multiplex circuit 126
on bus 127. The data is decoded into selection data on bus
132 (corresponding to input 102 in FIG. 5). When enable
line 133 goes high, the gain of mute circuit 121 decreases
from a given value, determined by the data in the register,
and then ramps up to the same value When the enable line
goes loW. Timer 134 times out a predetermined period While
the mute takes place, preventing control circuit 131 from
changing state during a transition in circuit 121.
[0053] All circuits aWait an enable signal from poWer-on
circuit 141 before becoming active. When poWer is applied
to the telephone, circuit 141 starts its oWn clock and Waits
a given number of clock cycles for other clocks (not shoWn)
in the telephone to stabiliZe. Other clocks, for example,
include 44.1 dual phase clocks used for sampling and
sWitched capacitor circuits (not shoWn) such as used for
?lters and time delay circuits. In one embodiment of the
invention, circuit 141 Waits thirty-tWo of its clock cycles,
then Waits ?ve milliseconds for all analog circuits to turn on
and stabiliZe. After the ?ve millisecond period, a logic “1”
is applied to poWer-on enable line 142.
[0054] The start-up procedure and operation of multiplex
circuit 126 are more easily understood from state diagrams.
A state machine is any circuit containing ?xed or program
mable sequential logic. In a given telephone, particularly a
speaker phone, there may be several state machines that
interact to provide the various functions of the telephone.
FIG. 8 is a block diagram of three modes of operation for
a telephone. The poWer-on portion of the poWer cycle is
described above. During this phase, all outputs are muted.
Similarly, during poWer-doWn, all outputs are muted prior to
poWer being shut off.
[0055] Mode 146, device transition, covers any change in
the operation of the telephone. Mode 147 is the steady state
operation of the telephone during a call, in either half-duplex
or full duplex mode. To change mode, the telephone reverts
to device transition mode 146 and enters the appropriate
state, as more fully described in connection With FIGS. 11
and 12.
[0056]
FIG. 9 illustrates the operation of the poWer-on
state machine. In FIG. 9, one enters On-Hook state 151 from
poWer-on reset 152. Suitable generators of a poWer-on reset
signal are Well knoWn per se in the art. On-Hook state 151
is entered regardless of the physical location of the handset;
ie whether or not the handset is in its cradle. The telephone
then enters stabiliZing state 152 for ?ve milliseconds, as
described above, then enters Off Hook state 154. At this
Jul. 3, 2003
US 2003/0123644 A1
point the start-up cycle is completed. Once completed, a
signal on line 142 (FIG. 7) causes the poWer-on state
machine to relinquish control to multiplex sequence state
machine 155, illustrated in FIG. 11. A poWer-doWn signal
causes the poWer on state machine to enter the On-Hook
state and remain there as long as the poWer-doWn signal
eXists.
poWer doWn signal, and at least one additional signal. If
there is also a handset enable signal, then the machine eXits
to state 172. In the process, the speaker output (of the base
receiver) is muted, the handset is unmuted (sequence 1), and
the line output is unmuted (sequence 1).
[0064]
If a call is being made, a DTMF enable signal
causes the machine to enter state 173 for the duration of the
[0057] FIG. 10 illustrates the mute sequence state
machine. ApoWer-on reset signal causes all the mute circuits
dialing, ending With a DTMF disable signal. The tones are
to enter a muted state. The state machine enters temporary
not coupled to the speakerphone.
state 160 and remains there until receiving a signal
(POSM13Done) that the poWer-on state machine is done, ie
the enable signal on line 142 (FIG. 7). In state 160, all muted
circuits are muted, Which assures that the initial operation of
the telephone does not cause any sounds in the speaker or
handset.
[0058] Actually, POSM13Done and one other signal are
necessary to eXit state 160. The other signal is either a mute
command or an unmute command. Assuming the
POSM13Done signal and mute command are given, the
machine enters hold mute state 161. As indicated by loop
162, the machine must stay in state 161 for at least ?ve
milliseconds after the state is ?rst entered. As indicated by
loop 163, state 161 is re-entrant, ie a stable state. After ?ve
milliseconds, only an unmute command can cause the
machine to eXit state 161.
audible in the handset and are sent to the line output but are
[0065]
The states Within arc 174 operate in full dupleX
mode and acoustic echo cancellation measures are unnec
essary and not enabled. Outside of arc 174, the system is
operating as a speakerphone and noise reduction circuitry
and echo cancelling circuitry, as described in the above
identi?ed applications, is enabled and disabled silently in
accordance With the invention.
[0066] From idle state 171, if a handset disable signal and
a receive disable signal are also received (With the PD
signal), then the machine enters half-duplex transmit state
175, in Which the handset is muted, the speakerphone is
unmuted and the line output is unmuted. From idle state 171,
if a handset disable signal and a receive enable signal are
also received, then the machine enters half-duplex receive
state 176, in Which the handset is muted, the speakerphone
receiver line is unmuted and the line output is muted. In
states 175 or 176, a receive enable or a receive disable signal
[0059] From state 160, an unmute command, and the
POSM13Done signal, causes the machine to enter unmute
Will sWitch the machine betWeen the tWo states, With the
state 164. As indicated by loop 165, the machine must stay
corresponding adjustment of outputs. While in either state
in state 164 for at least ?ve milliseconds after the state is ?rst
entered. After ?ve milliseconds, the machine Will eXit state
164 and enter either state 166 or state 167, depending upon
175 or 176, a handset enable signal With cause the machine
to sWitch to state 172. From state 172, a handset disable
signal and a receive disable Will return the machine to state
Whether or not the speaker phone is being used. If not, idle
state 167 is entered directly. If so, C13Hold state 166 is
entered for ?ve milliseconds, then eXited for idle state 167.
175. Ahandset disable signal and a receive enable Will return
the machine to state 176.
(1) identi?ed above, in Which a coarse delay and a ?ne delay
[0067] State 177 is entered from either state 175 or 176 in
response to a DTMF enable signal. State 177 is eXited When
a DTMF disable signal and either a receive enable signal is
are used in a circuit for eliminating echo. The ?ve millisec
received (for state 176) or a receive disable signal is received
ond delay in state 166 gives the echo cancelling circuitry
(for state 175).
[0060] The C13Hold state relates to copending application
time to lock onto the echo and stabiliZe. Acoustic echoes are
not relevant if the handset is being used. Thus, state 166 is
entered only if the speakerphone is being used.
[0061]
There are tWo paths out of idle state 167, depending
[0068] From either state 175 or 176, a half dupleX disable
signal Will cause the machine to enter state 179, in Which the
speakerphone is unmuted, the handset is muted, and the line
output is unmuted. The operation of the A/B shadoW state
mute command, the machine goes directly to state 161. If
there is an unmute command, the machine goes to temporary
mute state 168, Which mutes the line output for ?ve milli
machine is illustrated in greater detail in FIG. 12. State 179
is eXited to state 172 by a handset enable signal. State 179
is eXited to state 175 by a half-duplex enable signal and a
receive disable signal. State 179 is eXited to state 176 by a
seconds. The mute before unmute assures that one enters the
half-duplex enable signal and a receive enable signal.
upon Whether the command is mute or unmute. If there is a
unmute state With the line output muted for a quiet transi
tion.
[0069] FIG. 12 is a diagram illustrating the A/B shadoW
state machine Mode A (full dupleX), state 121, and mode B
[0062] To summariZe, three sequences are supported by
(full dupleX), state 122, relate to the complementary subsets
the mute sequence state machine: (1) muteQunmuteQidle,
(2) idleQmuteQunmuteQidle, and (3) idleQmute. One or
another of these sequences are applied to the three outputs
of ?lters. There are also three half dupleX states, states 123,
124, and 125. A half dupleX mode becomes necessary When
a telephone constructed in accordance With the invention is
(FIG. 7) by the multiplex sequence state machine.
used for conference calls of three or more parties.
[0063] FIG. 11 is the state diagram for the multipleX
[0070]
sequence state machine. From poWer on reset, the machine
enters idle state 171. Note that all states in the multipleX
sequence state machine are stable; ie the correct command
State 184 is entered by receiving a machine call. After a
the machine enters an idle state in Which essentially all
must be received to eXit along a particular path. All eXits
from state 171 require a PD signal, ie the absence of a
systems are off. Upon receipt of a call, the machine goes off
hook and enters state 184. In state 184, the machine is in half
State 184 is temporary and a half dupleX mode.
reset, represented by line 187, or the application of poWer,
Jul. 3, 2003
US 2003/0123644 A1
duplex mode While it looks for shadow signals indicating
that there are other machines in either A mode or B mode.
If no AshadoW is found, the machine enters state 181. If the
machine ?nds an A shadoW signal but no B shadoW signal,
state 182 is entered. If an A shadoW signal and a B shadoW
signal are found, then the machine enters state 183.
[0071] State 185 is typically entered by placing a call.
5. The method as set forth in claim 4 Wherein said device
includes a temporary mute state and Wherein the device can
proceed from idle to temporary mute to unmute to idle but
not the reverse.
6. In a telephone having a line input, a line output, a
handset microphone, and a handset speaker, the improve
ment comprising:
Unlike state 184, state 185 is not necessarily temporary
although the most likely outcome is that state 182 Will be
entered shortly after completing a connection to another
a ?rst soft mute circuit coupled to said handset micro
party. Path 195 corresponds to path 191, path 196 corre
sponds to path 192, and path 197 corresponds to path 193.
a second soft mute circuit coupled to said line input and
Entering either half dupleX state returns control to the
multipleX sequence state machine, either at state 175 (FIG.
7. The telephone as set forth in claim 6 Wherein said ?rst
soft mute circuit and said second soft mute circuit each
include:
11) if a receive enable command is received or state 176
(FIG. 11) if a receive disable command is received.
[0072]
The invention thus provides a method for removing
all audio artifacts from a telephone With no perceptible loss
of audio information. The telephone adapts silently to a
variety of possible operating conditions, Without interven
tion by a user, in manner that is transparent to the user.
[0073] Having thus described the invention, it Will be
apparent to those of skill in the art that various modi?cations
can be made Within the scope of the invention. For eXample,
While described as three state machines, such construction is
arbitrary. One could consider an entire telephone as a single
state machine. In mechanical terms, the invention can be
implemented With a single programmable logic device such
as a microprocessor or With a plurality of programmable or
?xed logic devices. The invention can be used With any
audio system, eg public address systems, intercoms, high
?delity systems, not just With telephones.
What is claimed as the invention is:
1. A method for removing unWanted audio artifacts in a
audio device, said method comprising the steps of:
operating the device in a ?rst mode;
changing mode only after muting the device; and
operating the device in a second mode only after unmut
ing the device.
2. The method as set forth in claim 1 Wherein the device
includes a plurality of outputs, said muting step includes the
steps of muting all the outputs, and the unmuting step
includes the step of selectively unmuting less than all the
outputs.
phone and said line output for attenuating audio arti
facts;
said handset speaker for attenuating audio artifacts.
an ampli?er having a gain control input for receiving
digital data and a signal input;
a register having an output coupled to said gain control
input;
an adder coupled to said register for storing data in said
register and having a pair of inputs, said adder having
a control input for adding or subtracting data on the
inputs of the adder;
Wherein said adder adjusts the gain of said ampli?er in
accordance With the signal on said control input.
8. In a speakerphone having a line input, a line output, a
microphone, and a speaker, the improvement comprising:
a ?rst soft mute circuit coupled to said microphone and
said line output for attenuating audio artifacts;
a second soft mute circuit coupled to said line input and
to said speaker for attenuating audio artifacts.
9. The speakerphone as set forth in claim 8 and further
including a handset microphone, a handset speaker, and a
third soft mute circuit coupled to said handset microphone
and said handset speaker.
10. The speakerphone as set forth in claim 9 Wherein said
handset microphone is also coupled to said ?rst soft mute
circuit.
11. The speakerphone as set forth in claim 9 Wherein said
?rst soft mute circuit, said second soft mute circuit, and said
third soft mute circuit each include:
an ampli?er having a gain control input for receiving
digital data and a signal input;
a register having an output coupled to said gain control
input;
3. The method as set forth in claim 2 Wherein said muting
an adder coupled to said register for storing data in said
step includes the step of increasingly attenuating an output
register and having a pair of inputs, said adder having
until a maXimum level of attenuation is reached.
4. The method as set forth in claim 1 Wherein said device
includes an idle state and a mute state as stable states and an
unmute state as a temporary state and Wherein said device
can proceed from idle to mute to unmute to idle but not the
reverse.
a control input for adding or subtracting data on the
inputs of the adder;
Wherein said adder adjusts the gain of said ampli?er in
accordance With the signal on said control input.
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