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JP2016510915

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DESCRIPTION JP2016510915
Abstract: A personal audio device comprising a plurality of output transducers for reproducing
different frequency bands of a source audio signal measures at least one microphone signal from
which ambient audio is measured to generate an anti-noise signal from each of the transducers
And an adaptive noise cancellation (ANC) circuit that adaptively generates an anti-noise signal.
The anti-noise signal is generated by a separate adaptive filter so that it causes a substantial
cancellation of the ambient audio in its corresponding converter. The use of a separate adaptive
filter results in short latency operation as crossover is not required to divide anti noise into the
appropriate frequency band. The adaptive filter can be implemented or biased to generate antinoise only in the frequency band corresponding to the particular adaptive filter. The anti-noise
signal is combined with source audio in the appropriate frequency band to provide an output for
the corresponding converter.
Low-latency multi-driver adaptive noise cancellation (ANC) system for personal audio devices
[0001]
FIELD OF THE INVENTION The present invention relates generally to personal audio devices that
include adaptive noise cancellation (ANC) and multiple drivers for different frequency bands.
[0002]
BACKGROUND OF THE INVENTION Mobile / mobile phones, wireless phones such as cordless
phones, and other consumer audio devices such as MP3 players are widely used.
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The performance of such devices with respect to intelligibility provides an ANC using a reference
microphone that measures ambient acoustic events, and then uses signal processing to insert an
anti-noise signal at the output of the device, It can be improved by eliminating acoustic events.
[0003]
Most audio systems implemented for personal audio devices rely on a single output transducer,
but when the transducer or ear speaker mounted on the radio telephone housing is used, or
wireless In the case of a pair of transducers when the telephone or other device employs stereo
speakers, separate transducers for high and low frequencies, as in high quality ear speakers, for
high quality audio reproduction. It may be desirable to provide. However, when implementing
ANC in such a system, the latency introduced by the crossover that splits the signal between the
low frequency converter and the high frequency converter introduces a delay, which increases
the operation The effectiveness of the ANC system is reduced due to the latency.
[0004]
Accordingly, it would be desirable to provide a personal audio system that includes a wireless
telephone and / or ear speakers that provide short latency ANC operation while using multiple
output transducers that handle different frequency bands.
[0005]
SUMMARY OF THE INVENTION The above stated objects of providing a personal audio device
having an ANC and employing multiple output transducers to handle different frequency bands
are achieved in a personal audio system, method of operation and integrated circuit Be done.
[0006]
The personal audio device is a low frequency output transducer and high frequency to reproduce
the source audio signal for playback to the listener and an anti-noise signal to cancel out the
effects of ambient audio sound on the transducer's acoustic output. Includes both transducers.
Personal audio devices also include integrated circuits that provide adaptive noise cancellation
(ANC) functionality.
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The method is a method of operating a personal audio system and an integrated circuit. A
reference microphone is mounted on the device housing to provide a reference microphone
signal indicative of ambient audio sound. The personal audio system further includes an ANC
processing circuit for adaptively generating an anti-noise signal from the reference microphone
signal such that the anti-noise signal causes substantial cancellation of ambient audio sound in its
corresponding converter. Including. An adaptive filter is used to generate an anti-noise signal by
filtering the reference microphone signal.
[0007]
The foregoing and other objects, features, and advantages of the present invention will be
apparent from the following more particular description of the preferred embodiments of the
present invention, as illustrated in the accompanying drawings.
[0008]
FIG. 1A is an illustration of an exemplary wireless telephone 10 and a pair of earphones EB1 and
EB2.
FIG. 1B is a schematic diagram of the circuitry within the wireless telephone 10. FIG. 2 is a block
diagram of a circuit inside the radio telephone 10. As shown in FIG. FIG. 3 is a block diagram
depicting the signal processing circuits and functional blocks of various exemplary ANC circuits
that may be used to implement the ANC circuit 30 of the CODEC integrated circuit 20A of FIG.
FIG. 4 is a block diagram depicting signal processing circuitry and functional blocks within
CODEC integrated circuit 20. As shown in FIG.
[0009]
Best Mode for Implementing the Invention The present invention encompasses noise cancellation
techniques and circuitry that may be implemented in a personal audio system such as a wireless
telephone and connected earphones. The personal audio system attempts to measure and cancel
the ambient acoustic environment at an earphone or other output transducer location, such as on
an enclosure of a personal audio device that receives or generates source audio signals. Adaptive
noise Includes an erase (ANC) circuit. In order to provide high quality audio output, multiple
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converters are used, including low frequency and high frequency converters that reproduce the
frequency band of the corresponding source audio. The ANC circuit generates a separate antinoise signal that is provided to each one of the plurality of transducers to cancel ambient
acoustic events at the transducers. A reference microphone is provided to measure the ambient
acoustic environment, such that low latency is maintained by eliminating the need for crossovers
to filter out the generated anti-noise. Provide an input to a separate adaptive filter that generates
a signal. The source audio crossover can then be placed in advance of the adder of the source
audio frequency band specific component and its corresponding anti-noise signal, the adaptive
filter being suitable for its corresponding converter The noise can be controlled to generate antinoise only within a certain frequency range.
[0010]
FIG. 1A shows a radiotelephone 10 and a pair of earphones EB1 and EB2 attached to the
corresponding ears 5A, 5B of the listener respectively. The illustrated wireless telephone 10 is an
example of a device in which the techniques disclosed herein may be employed, but all the
elements or configurations illustrated within the circuit depicted in the wireless telephone 10 or
subsequent illustrations It should be understood that it is not required. The wireless telephone
10 has a wired or wireless connection, for example, BLUETOOTH (registered trademark)
connection (BLUETOOTH (registered trademark) is Bluetooth (registered trademark) SIG, Inc. Is
connected to the earphones EB1, EB2. The earphones EB1, EB2 respectively source audio,
including remote speech, ringing tones, stored audio program material, and input of near-end
speech (ie, speech of the user of the wireless telephone 10) received from the wireless telephone
10. Each has a corresponding pair of transducers SPKLH / SPKLL and SPKRH / SPKRL to be
reproduced. The converters SPKLH and SPKRH are high frequency converters or "tweeters" that
reproduce the audio frequency and the higher range of the converter SPKLL, and the SPKRL is a
low frequency converter or that reproduces a lower range of audio frequencies. It is a "woofer".
Source audio is also required for the radiotelephone 10 to reproduce source audio from web
pages or other network communications received by the radiotelephone 10 and audio metrics
such as low battery and other system event notifications. , Including any other audio. Reference
microphones R1, R2 are provided on the surface of the housing of the individual earphones EB1,
EB2 to measure the ambient acoustic environment. Another pair of microphones, the error
microphones E1, E2, each pair of transducers that are close to the corresponding ear 5A, 5B
when the earphones EB1, EB2 are inserted into the outer part of the ear 5A, 5B It is provided to
further improve ANC operation by providing ambient audio measurements combined with audio
reproduced by SPKLH / SPKLL and SPKRH / SPKRL.
[0011]
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The radiotelephone 10 applies an anti-noise signal to SPKLH, SPKLL, SPKRH, and SPKRL to
improve the clarity of remote speech and other audio reproduced by the transducers SPKLH,
SPKLL, SPKRH, and SPKRL. Includes erase (ANC) circuits and features. Exemplary circuitry 14
within wireless telephone 10 includes an audio integrated circuit 20 that receives signals from
reference microphones R1, R2, proximity speech microphones NS, and error microphones E1, E2,
and is an RF integrated that contains a wireless telephone transceiver It interfaces with other
integrated circuits such as circuit 12. In other implementations, the circuits and techniques
disclosed herein are a single integrated circuit containing control circuitry and other
functionality for implementing the entire personal audio device such as an MP3 player on chip
integrated circuit. It may be incorporated inside. Alternatively, the ANC circuit may be included in
the housing of the earphones EB1, EB2 or in a module located along the wired connection
between the radiotelephone 10 and the earphones EB1, EB2. Although the ANC circuit is
described as being provided in the radiotelephone 10 for the purpose of illustration, the
aforementioned variations are comprehensible by those skilled in the art and the earphones EB1,
EB2, the radiotelephone 10, and The resulting signals required between the third modules can be
easily determined for those variations, as required. The near speech microphone NS captures
near-end speech that is provided to the housing of the wireless telephone 10 and transmitted
from the wireless telephone 10 to other speech participants. Alternatively, the close-talking
microphone NS may be on the outer surface of one of the housings of the earphones EB1, EB2,
on a support attached to one of the earphones EB1, EB2, or one or both of the radiotelephone 10
and the earphones EB1, EB2. And an appendage located between them.
[0012]
FIG. 1B shows a reference microphone R1, providing measurements of ambient audio ambient 1,
ambient 2, filtered by ANC processing circuits in the audio integrated circuits 20A, 20B located
in the corresponding earphones EB1, EB2. FIG. 6 shows a simplified schematic of an audio
integrated circuit 20A, 20B, including ANC processing, as coupled to R2. Audio integrated
circuits 20A, 20B may alternatively be combined in a single integrated circuit such as integrated
circuit 20 in radiotelephone 10. The audio integrated circuits 20A, 20B are amplified by the
associated one of the amplifiers A1-A4 and provided to the corresponding converter pair SPKLH
/ SPKLL and SPKRH / SPKRL, the output for that corresponding channel generate. The audio
integrated circuits 20A, 20B receive (wired or wireless depending on the specific configuration)
signals from the reference microphones R1, R2, the close speech microphone NS, and the error
microphones E1, E2. Audio integrated circuits 20A, 20B also interface with other integrated
circuits, such as RF integrated circuit 12, including the radiotelephone transceiver shown in FIG.
1A. In other configurations, the circuits and techniques disclosed herein are a single integrated
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circuit that contains control circuitry and other functionality for implementing the entire
personal audio device such as an MP3 player on chip integrated circuit. It may be incorporated
inside. Alternatively, the plurality of integrated circuits may, for example, be provided when the
wireless connection is provided to the wireless telephone 10 from each of the earphones EB1,
EB2, and / or some or all of the ANC processing may be performed by the earphones EB1, EB2 or
the wireless telephone 10 may be used when performed in a module disposed along a cable
connecting the earphones EB1, EB2.
[0013]
In general, the ANC techniques illustrated herein measure ambient acoustic events (as opposed to
transducers SPKLH, SPKLL, SPKRH, and SPKRL and / or near-end speech) colliding with
reference microphones R1, R2. And measure the same ambient acoustic event that collides with
the error microphones E1, E2. The ANC processing circuit of integrated circuits 20A, 20B
individually adapts the anti-noise signal generated from the output of the corresponding
reference microphone R1, R2 and minimizes the amplitude of the ambient acoustic event in the
corresponding error microphone E1, E2 Limit characteristics. Since the acoustic path P L (z)
extends from the reference microphone R1 to the error microphone E1, the ANC circuits in the
audio integrated circuit 20A essentially each respond to the audio output circuit of the audio
integrated circuit 20A, Estimate the combined acoustic path P L (z) with the effects of the
electroacoustic paths S LH (z) and S LL (z) representing the acoustic / electrical transfer
functions of the transducers SPKLH and SPKLL There is. The estimated response is influenced by
the proximity and structure of the ear 5A and other physical objects that may be close to the
earphone EB1 and the human head structure, the transducers SPKLH and SPKLL and the error
microphone E1 in a specific acoustic environment And the bond between Similarly, audio
integrated circuit 20B represents the response of the audio output circuit of audio integrated
circuit 20B and the acoustic / electrical transfer function of transducers SPKRH and SPKRL,
respectively, electro-acoustic path S RH (z), and S RL (z The combined acoustic path P R (z) is
estimated with the influence of) removed.
[0014]
Referring now to FIG. 2, the circuitry within the earphones EB1, EB2 and the radiotelephone 10
is shown in a block diagram. Although the circuit shown in FIG. 2 is further applied to the other
configurations described above, the audio integrated circuits 20A and 20B are in charge of signal
transmission between the CODEC integrated circuit 20 and the other units in the radiotelephone
10. When located outside the wireless telephone 10, for example, in the corresponding
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earphones EB1, EB2, it is provided by a cable or a wireless connection. In such a configuration,
signaling between a single integrated circuit 20 implementing integrated circuits 20A-20B and
error microphones E1, E2, reference microphones R1, R2, and transducers SPKLH, SPKLL,
SPKRH, and SPKRL. Is provided by a wired or wireless connection when the audio integrated
circuit 20 is located in the wireless telephone 10. In the illustrated embodiment, the audio
integrated circuits 20A, 20B are shown as separate and substantially identical circuits, and thus
only the audio integrated circuit 20A is described in detail below.
[0015]
The audio integrated circuit 20A includes an analog / digital converter (ADC) 21A that receives a
reference microphone signal from a reference microphone R1 and generates a digital
representation ref of the reference microphone signal. The audio integrated circuit 20A also
receives an error microphone signal from the error microphone E1, an ADC 21B for generating a
digital representation err of the error microphone signal, and a close speech microphone signal
from the close speech microphone NS, and the close speech microphone signal And an ADC 21C
for generating a digital representation ns of. (The audio integrated circuit 20B receives the digital
representation ns of the close speech microphone signal from the audio integrated circuit 20A
via the wireless or wired connection as described above. The audio integrated circuit 20A
receives an output of the coupler 26A, amplifies an output of the digital / analog converter (DAC)
23A, and generates an output for driving the converter SPKLH from the amplifier A1. A combiner
26C combines the left channel internal audio signal ial with the source audio ds, which is
received from a radio frequency (RF) integrated circuit 22. The combiner 26A combines the
source audio d sh + ial h, which is the high frequency band component of the output of the
combiner 26C with the high frequency band anti-noise l h generated by the left channel ANC
circuit 30 , Typically of the same polarity as the noise in the reference microphone signal ref, and
thus subtracted by the coupler 26A. The combiner 26A also attenuates the high frequency part
of the close speech signal ns, ie the sidetone information, so that the user of the radiotelephone
10 can hear its own speech properly in connection with the downlink speech ds. Combine st h
The near speech signal ns is also provided to the RF integrated circuit 22 and transmitted to the
service provider as uplink speech via the antenna ANT. Similarly, left channel audio integrated
circuit 20A generates an output from amplifier A2 for driving converter SPKLL, which outputs
the output of digital-to-analog converter (DAC) 23B receiving the output of coupler 26B. To
amplify. The combiner 26B combines the source audio ds l + i a ll, which is the low frequency
component of the output of the combiner 26 C with the low frequency antinoise signal anti-noise
ll generated by the ANC circuit 30, typically , Of the same polarity as the noise in the reference
microphone signal ref, and thus subtracted by the combiner 26B.
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The combiner 26B also combines the attenuated part of the close speech signal ns, ie the
sidetone low frequency information st l.
[0016]
Referring now to FIG. 3, an example of details internal to ANC circuit 30 as may be used to
implement audio integrated circuit 20B of FIG. 2 is shown. The same circuit is used to implement
the audio integrated circuit 20A, with changes to the inside of the channel indicator diagram as
noted below. High frequency channel 50A and low frequency channel 50B, respectively, are
provided to generate anti-noise signals anti-noise rh and anti-noise rl. The signal and response
indicators contain the letter "r" indicating the right channel, in the following description, the
letters are in another circuit according to Fig. 3 as implemented within the audio integrated
circuit 20A of Fig. 2 It will be replaced with "l" indicating the left channel. If the signal and
response are labeled with the letter "h" for low frequency in high frequency channel 50A, then
the corresponding element in low frequency channel 50B is the signal and response labeled with
the letter "l" Will be replaced. An adaptive filter 32A receives the reference microphone signal ref
and, under ideal conditions, adapts its transfer function W rh (z) to be P r (z) / S rh (z) to reduce
the anti-noise signal anti- Generate noise rh. The coefficients of the adaptive filter 32A generally
use the correlation of the two signals to minimize errors between those components of the
reference microphone signal ref present in the microphone signal err in a least mean square
sense It is controlled by the W coefficient control block 31A which determines the response of
the adaptive filter 32A. While the embodiments disclosed herein use adaptive filters 32A
connected in a feedforward configuration, the techniques disclosed herein are implemented in a
noise cancellation system with fixed or programmable filters Disclosed herein if the coefficients
of the adaptive filter 32A are preset, selected, or otherwise not successively applied, or
alternatively or in combination with a fixed filter topology. The techniques to be applied can be
applied to feedback ANC systems or hybrid feedback / feed forward ANC systems. The signal
provided as input to the W coefficient control block 31A is provided from the copy of the
estimate of the response of the path S rh (z) provided by the filter 34B and from the output of the
combiner 36C including the error microphone signal err A reference microphone signal ref as
shaped by another signal.
Transform the reference microphone signal ref with a response SE rhCOPY (z), which is a copy of
the response estimate of path S rh (z), to minimize the portion of the error signal that correlates
with the components of the reference microphone signal ref The adaptive filter 32A adapts to the
desired response of P r (z) / S rh (z).
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[0017]
In addition to the error microphone signal err, it has the response SE rh (z) (the response SE
rhCOPY (z) is its copy) as another signal to be processed with the output of the filter 34B by the
W coefficient control block 31A, 2 It contains the inverse quantity of the source audio (ds + ia r),
which is processed by the next path filter 34A, including the downlink audio signal ds and the
internal audio ian. First, before the source audio (ds + ia r) is provided by the high pass filter 35A
to the high frequency channel 50A, it is filtered, which passes only the frequency introduced by
the high frequency converter SPKLH or SPKRH. Similarly, first, the source audio (ds + ia r)
provided to the low frequency channel 50B is filtered by the low pass filter 35B, which passes
only the frequencies provided by the low frequency converter SPKLL or SPKRL . Thus, high pass
filter 35A and low pass filter 35B form a crossover to the source audio (ds + ia r) such that only
the appropriate frequency is passed to high frequency channel 50A and low frequency channel
50B, respectively There is an appropriate bandwidth for each converter SPKLH, SPKLL, or
SPKRH, SPKRL. By injecting the inverse quantity of the source audio (ds + ia r) filtered by the
response SE rh (z), the adaptive filter 32A will not adapt to the relatively large amount of source
audio present in the error microphone signal err To prevent. By converting the reciprocal copy of
the source audio (ds + ia r) with the estimate of the response of the path S rh (z), the source audio
removed from the error microphone signal err before processing is reproduced in the error
microphone signal err Should match the expected version of the source audio (ds + ia r). The
source audio amount is matched because the electrical and acoustic path of S rh (z) is the path
followed by the source audio (ds + ia r) to reach the error microphone E. The filter 34B is not
itself an adaptive filter, but is tuned to match the response of the filter 34B to the response of the
secondary path adaptive filter 34A so as to track the adaptation of the secondary path adaptive
filter 34A. , Have adjustable response.
To implement the foregoing, the secondary path adaptive filter 34A has coefficients that are
controlled by the SE coefficient control block 33A. The secondary path adaptive filter 34A
processes low or high frequency source audio (ds + ia r) and provides a signal representing the
expected source audio delivered to the error microphone E. The secondary path adaptive filter
34A thereby produces a signal that forms an error signal e which, when subtracted from the
error microphone signal err, contains the content of the error microphone signal err not
originating from the source audio (ds + ia r) Adapted to originate from (ds + ia r). A combiner
36C removes the filtered source audio (ds + ia r) from the error microphone signal err and
generates the aforementioned error signal e.
[0018]
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Each of the high frequency channel 50A and the low frequency channel 50B can operate
independently to generate their respective anti-noise signals anti-noise h and anti-noise 1.
However, since the error signal e and the reference microphone signal ref may contain
frequencies of any frequency within the audio band without band limiting the anti-noise signals
anti-noise h and anti-noise l, their respective It may contain components that should not be sent
to the high frequency and low frequency converters SPKRH / SPKLH and SPKRL / SPKLL.
Therefore, noise injection techniques are used to control the response W rh (z) of the adaptive
filter 32A. A noise source 37 generates an output noise signal n h (z) which is supplied to a copy
W rhCOPY (z) of the response W rh (z) of the adaptive filter 32A provided by the adaptive filter
32B. A combiner 36A adds the noise signal n h (z) to the output adaptive filter 34B, which is
provided to the W coefficient control 31A. The noise signal n h (z) as shaped by the filter 32B is
combined by the combiner 36 B such that the noise signal n h (z) is asymmetrically added to the
correlated input to the W coefficient control 31A Subtracted from the output of 36 C so that the
response W rh (z) of the adaptive filter 32 A is biased by the fully correlated input of the noise
signal n h (z) at each correlation input to the W coefficient control 31 A Ru. Input noise appears
directly in the reference input to the W coefficient control 31A and does not appear in the error
microphone signal err, via the combination of the filtered noise at the output of the filter 32B by
the coupler 36B, the W coefficient control 31A. The W coefficient control 31 A will adapt W rh
(z) to attenuate the frequencies present in n h (z), as it only appears at the other inputs to it. The
content of the noise signal n h (z) does not appear in the anti-noise signal, and the response W rh
(z of the adaptive filter 32A will have an amplitude reduction at the frequency / band the noise
signal n h (z) has energy. Appears only in).
[0019]
In order to prevent low frequencies from being generated in the anti-noise signal anti-noise h, the
noise source 37 generates noise with a spectrum having energy in the low frequency band, which
has a W-factor control 31A will reduce the gain of the adaptive filter 32A within these low
frequency bands in an attempt to cancel the apparent source of ambient acoustic sound due to
the input noise signal n h (z). For example, a white noise source may be filtered with a response
similar to that of low pass filter 35B for use as noise source 37 in high frequency channel 50A,
which may be applied to adaptive filter 32A as low pass filter 35B. It would have low gain in the
region of the passband of By filtering the white noise source with a response that is identical to
that of the low frequency channel 50B, ie, the response of the high pass filter 35A, the crossover
is achieved by the respective anti-noise signals anti-noise h and It is effectively formed by the
adaptation of the adaptive filter 32A in the high frequency channel 50A and the low frequency
channel 50B to prevent unwanted frequencies in the anti-noise 1. A similar construction may be
formed around the secondary path adaptive filter 34A, but the input to the secondary path
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adaptive filter 34A is already taken by each one of the filters 35A and 35B to remove it from the
band energy. Because it is filtered, such noise injection should not be required to remove
unwanted frequencies from the output of the secondary path adaptive filter 34A. One of the
advantages of using noise injection rather than additive filtering to remove unwanted crossover
energy from the anti-noise signals anti-noise h and anti-noise l is that the additional latency is a
noise source It is not introduced except for any waiting time due to the change of response due
to 37.
[0020]
Referring now to FIG. 4, a block of ANC system for implementing the ANC technique as depicted
in FIG. 3 and having processing circuitry 40 as may be implemented in the audio integrated
circuits 20A, 20B of FIG. The figures are shown and illustrated as being combined in one circuit,
but may also be implemented as two or more processing circuits in communication with each
other. The processing circuit 40 comprises a processor core 42 coupled to a memory 44 storing
program instructions, including a computer program product, which may implement some or all
of the aforementioned ANC techniques as well as other signal processing. Optionally, special
purpose digital signal processing (DSP) logic 46 may be provided to implement some or all of the
ANC signal processing provided by processing circuit 40. The processing circuit 40 also includes
ADCs 21A-21E to receive inputs from the reference microphone R1, the error microphone E1,
the close speech microphone NS, the reference microphone R2, and the error microphone E2,
respectively. In an alternative embodiment, one or more of reference microphone R1, error
microphone E1, close speech microphone NS, reference microphone R2, and error microphone
E2 have digital outputs or are communicated as digital signals from a remote ADC The
corresponding one of the ADCs 21A-21E is omitted, and the digital microphone signal is directly
interfaced to the processing circuit 40. DAC 23A and amplifier A1 are also provided by
processing circuit 40 to provide a converter output signal to converter SPKLH, which includes
anti-noise as described above. Similarly, DACs 23B-23D and amplifiers A2-A4 provide other
converter output signals to converter pairs SPKLH, SPKLL, SPKRH, and SPKRL. The transducer
output signal may be a digital output signal for providing to a module that acoustically
reproduces the digital output signal.
[0021]
Although the present invention has been particularly illustrated and described with reference to
its preferred embodiments, the foregoing and other variations in form and detail may be made
herein without departing from the spirit and scope of the present invention. It will be understood
by those skilled in the art that it may.
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