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DESCRIPTION JP2017532816

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DESCRIPTION JP2017532816
Abstract: The system and method comprises positioning a mobile device with an integrated
loudspeaker in a first position of the listening environment and at least one microphone in at
least one second position of the listening environment; Emitting test audio content from the
loudspeakers of the mobile device at the position of h, receiving the test audio content emitted by
the loudspeakers using at least one microphone of the at least one second position of the
listening environment; Determining, based at least in part on the received test audio content, one
or more adjustments to be applied to the desired audio content before being played by the at
least one earphone; The second positions are separated from each other, One microphone is in
the near field of the loudspeaker.
Voice reproduction system and method
[0001]
The present disclosure relates to audio reproduction systems and methods, and in particular to
highly personalized audio reproduction systems and methods.
[0002]
There are many algorithms in the market for binaural reproduction of audio content via
earphones.
Those algorithms are based on synthetic binaural room impulse response (BRIR), which is based
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on general HRTFs, such as standard dummy heads or general functions of large head transfer
function (HRTF) databases. Means to be based. Furthermore, some algorithms allow the user to
select the most appropriate BRIR from a given set of BRIRs. Such options can improve listening
quality. Such options include externalization and out-of-head localization, but personalization
(e.g., head shadowing, shoulder reflex or pinnacle effect) has left the signal processing chain. In
particular, pinnacle information is unique, like fingerprints. Naturalness can be improved by
adding individual BRIR personalization.
[0003]
The method described herein comprises a mobile device having a built-in speaker at a first
position of the listening environment, placing at least one microphone at at least one second
position of the listening environment, and Emitting test audio content from the loudspeaker of
the mobile device at position 1; receiving test audio content emitted by the loudspeaker using at
least one microphone at at least one second position of the listening environment; Determining,
based at least in part on the received test audio content, one or more adjustments to be applied
to the desired audio content before being played by the at least one earphone; The second
positions are separated from one another and at least one The microphone is in the near field of
the loudspeaker.
[0004]
A system for measuring a binaural room impulse response comprises: a mobile device with an
integrated speaker located at a first position of the listening environment; and at least one
microphone located at at least one second position of the listening environment Prepare.
The mobile device emits test audio content through the loudspeaker at a first position of the
listening environment, the loudspeaker emits test audio content received by the earphone at at
least one second position of the listening environment from the earphone Configured to receive.
The mobile device is further configured to determine, based at least in part on the received audio
content, one or more adjustments that the mobile device applies before being played by the
earphone to the desired audio content, the first And the second position are remote from one
another, at least one microphone being in the near field of the loudspeaker.
[0005]
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Other systems, methods, features, and advantages will be, or will become, apparent to one with
skill in the art upon examination of the following detailed description and drawings. It is intended
that all such additional systems, methods, features and advantages be within the scope of this
description, be within the scope of the invention, and be protected by the following claims.
[0006]
The system will be better understood with reference to the following description and drawings.
The components in the drawings are not necessarily to scale, emphasis instead being placed
upon illustrating the principles of the invention. Further, in the figures, like reference numerals
indicate corresponding parts throughout the different views.
[0007]
FIG. 5 is a schematic diagram illustrating an exemplary audio system for binaural reproduction of
a 2-channel stereo, 5.1-channel stereo, or 7.1-channel stereo signal. FIG. 1 is a schematic diagram
illustrating an example system for measuring BRIR using a smartphone and a mobile microphone
recorder. FIG. 7 is a schematic diagram illustrating another exemplary system for measuring
BRIR using a smartphone and a headphone microphone. 5 is a flow chart illustrating an
exemplary method of measuring BRIR using a smartphone. FIG. 5 shows frequency responses to
different stimuli. FIG. 7 shows the frequency response of a rear smartphone loudspeaker
(obtained from a close range measurement), an exemplary target frequency response, and an
inverse filter. FIG. 7 is a flow chart illustrating an example application of BRIR measurements to a
headphone real room system. FIG. 7 is a flow chart illustrating an exemplary method of
computing an inverse filter to correct a smartphone speaker defect. It is a figure which shows the
comparison of the frequency response before and behind correcting the defect of the speaker of
a smart phone. 3 is a flow chart illustrating an exemplary spectrum balancer algorithm. FIG. 1 is
a schematic diagram illustrating an exemplary device for measuring earphone characteristics. 5
is a flowchart illustrating an example earphone equalizer algorithm. FIG. 7 is a flow chart
illustrating an example application of BRIR measurements in a headphone virtual room system.
FIG. 5 is a diagram showing a window function used in the dereverberation apparatus. It is a
figure which shows BRIR before and behind applying the window function shown in FIG. FIG. 7
shows a comparison of the amplitude response of various exemplary measured BRIRs. Fig. 17
shows a comparison of the phase response of an exemplary measured BRIR forming the basis of
the diagram shown in Fig. 16; FIG. 6 shows the amplitude response of an earphone transducer
used as a microphone.
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[0008]
The recorded "surround sound" is typically conveyed through five, six, seven or eight or more
speakers. Real-world sounds reach users from infinity (also referred to herein as "listeners",
particularly when it relates to the user's acoustic perception). The human auditory system is a
two-channel system, but the listener can easily sense the direction on all axes in threedimensional space. One path to the human auditory system is via headphones (herein also
referred to as "earphones" when it comes to the auditory behavior for each ear). The weakness of
headphones is that they can not produce a three-dimensional, extensive, completely accurate
sound image. Some "virtual surround" processors have advanced in this respect in stages, and
headphones are, in principle, as complete, spacious, accurate as created by multiple speakers in a
real room Can provide a lively sound experience that has been localized.
[0009]
The sound coming from different directions changes when it collides with the shape and size of
the head and upper torso and the shape of the outer ear (auricle). The human brain is very
sensitive to these changes and is experienced fairly accurately by the listener as identifying the
top, bottom, front, back, or between and without being perceived as a change in timbre Ru. This
acoustic change can be represented by the HRTF.
[0010]
With one kind of recording, it turned out that two audio channels can reproduce a threedimensional experience. Binaural recordings are performed using a pair of closely placed
microphones and are intended for headphone listening. Sometimes the microphone is embedded
in the dummy head or head / body to create HRTFs, in which case the sense of three
dimensionality is enhanced. Although the reproduced sound space is understandable, its
accuracy can not be proved because it does not refer to the original environment. In any case,
these are special recordings that are rarely seen in commercial catalogs. Front, back, and
sometimes, recordings to capture overhead sounds are performed using multiple microphones
and are intended to be stored on multiple channels and played on multiple speakers placed
around the listener doing.
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[0011]
Other systems (Smyth Realiser, etc.) offer completely different experiences. That is, in multichannel recordings (including stereo), the same sound is emitted through the headphones
indistinguishably from that emitted through the loudspeaker array in a real room. In principle,
Smyth Realiser is similar to other systems in that it applies HRTFs to multi-channel sound to
drive headphones. However, along with other improvements, Smyth Realiser employs three key
components not found in other products: personalization, head tracking, and capture of any real
listening space and sound system characteristics. doing. The Smyth Realiser comprises a pair of
tiny microphones inserted into the earplugs, which are placed on the listener's ear for
measurement. The listener sits at a listening position surrounded by a loudspeaker array.
Typically, any setting may be applied, although it is a 5.1 or 7.1 channel, but a height channel. A
short test signal set is played through the loudspeaker, and then the listener wears headphones
and obtains a second short set of measurements. The entire procedure is less than 5 minutes. In
the measurements with loudspeakers, Smyth Realiser not only captures the listener's personal
HRTFs, but also completely characterizes the room, the loudspeakers and the electronics driving
the loudspeakers. In measurements using headphones, the system collects data to correct the
headphone-ear interaction and the response of the headphones themselves. The synthesized data
is stored in memory, and the synthesized data can be used to control an equalizer connected to
the audio signal path.
[0012]
Thus, the effort required to perform binaural measurements is cumbersome as it requires
dedicated measurement microphones, sound cards, and other equipment. The methods and
systems described herein enable measurement of BRIR with a smartphone to facilitate binaural
measurements without using expensive hardware.
[0013]
FIG. 1 is a schematic diagram of an exemplary audio system 100 for binaural reproduction of the
two channel stereo, 5.1 channel stereo, or 7.1 channel stereo signals provided by signal source
101. The signal source may be a CD player, a DVD player, a vehicle head unit, an MPEG Surround
Sound (MPS) decoder or the like. The binauralizer 102 generates a two-channel signal for the
earphone 103 from the two-channel stereo, 5.1-channel stereo, or 7.1-channel stereo signal
provided by the signal source 101. The BRIR measurement system 104 enables measurement of
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the actual BRIR and provides a signal representing the BRIR to the binauralizer 102 so that multichannel recordings (including stereo) can be output through the loudspeaker array in a real
room. The same sound comes out through the earphone 103 indistinguishably. The exemplary
audio system 100 shown in FIG. 1 may be used to convey personalized multi-channel content for
automotive applications, and is intended for all types of headphones (ie, in-ear headphones as
well as on-ear headphones). It is good.
[0014]
FIG. 2 is a schematic diagram of an exemplary BRIR measurement system 104 using a smart
phone 201 (or mobile phone, Fablet, tablet, laptop, etc.) connected to a loudspeaker 202 and two
microphones 204, 205. And a mobile voice recorder 203. The loudspeaker 202 of the
smartphone 201 establishes an acoustic transmission path 206 between the loudspeaker 202
and the microphones 204, 205 by emitting the sound captured by the microphones 204, 205.
Digital data, including digital audio signals and / or instructions, are exchanged between the
smart phone 201 and the recorder 203 via the bi-directional wireless connection 207. The twoway wireless connection 207 may be a Bluetooth® (BT) connection.
[0015]
FIG. 3 is a schematic diagram of another exemplary BRIR measurement system 104 using a smart
phone 301, including a loudspeaker 302 and a headphone 303 with microphones 304, 305. The
loudspeaker 302 of the smartphone 301 establishes an acoustic transmission path 306 between
the loudspeaker 302 and the microphones 304, 305 by emitting the sound captured by the
microphones 304, 305. Digital or analog audio signals are transmitted from the microphones
304, 305 to the smart phone 301 by a wired connection 307 or by a wireless connection such as
a BT connection (not shown in FIG. 3). The same or separate wired or wireless connections (not
shown in FIG. 3) may be used to convey digital or analog audio signals from the smartphone 301
to the headphones 303 for playback of these audio signals.
[0016]
Please refer to FIG. A start command from a user may be received by a mobile device such as
smartphone 201 of the system shown in FIG. 2 (procedure 401). When the start command is
received, the smartphone 201 starts a dedicated software application (app) to establish a BT
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connection with the mobile voice recorder 203 (procedure 402). The smartphone 201 receives a
recording command from the user and instructs the mobile voice recorder 203 to start recording
via the BT connection 207 (procedure 403). The mobile voice recorder 203 receives the
command from the smartphone 201 and starts recording (procedure 404). The smartphone 201
emits test audio content via the built-in speaker 202, and the mobile audio recorder 203 records
the test audio content received by the microphones 204 and 205 (procedure 405). The
smartphone 201 instructs the mobile voice recorder 203 to stop recording via BT (procedure
406). The mobile voice recorder 203 receives the command from the smartphone 201 and stops
the recording (procedure 407). Next, the mobile voice recorder 203 transmits the recorded test
voice content to the smartphone 201 via the BT (procedure 408), and the smartphone 201
receives the test voice content recorded from the mobile voice recorder 203 and receives the test
Process audio content (procedure 409). The smartphone 201 then disconnects the BT connection
with the mobile recorder (procedure 410) and outputs data representing BRIR (procedure 411).
A process similar to that shown in FIG. 4 may be applied to the system shown in FIG. 3, but voice
recording is performed within the mobile device (smart phone 301).
[0017]
In the study, four stimuli (test audio content) were considered in relation to the exemplary
system shown in FIG. The balloon is broken 501, two different types of applauses 502, 503, and
a sine wave sweep 504. These stimuli were recorded approximately 1 meter from a specific
measuring microphone in the anechoic chamber. The amplitude of the impulse response of these
measurements is shown in FIG. It can be seen from the graph that the current shape is not ideal
because the two applauses 502, 503 are significantly different from the measurements of the
sinusoidal sweep 504. Also shown is impulse stimulus 505 for comparison. The frequency
response should ideally be measured in an anechoic chamber. However, non-experts can not
usually be approached except by experts. Instead, use near-field measurement. Near-field
measurement is technically feasible by using the same microphone as used for binaural
measurements. Thus, a single applause recording does not necessarily provide the desired
characteristics of the room. Thus, more practical attempts from end users are needed to make
measurements. However, it is desirable to create a measurement procedure that is as simple as
possible and reliable for general users.
[0018]
Acoustic sources such as loudspeakers have both near field and far field regions. In the near field,
the wavefronts generated by the loudspeakers (or loudspeakers for short) are not parallel and the
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wave strength oscillates with the range. Because of this, the level of echoes from targets in the
near field region can vary greatly with a slight change in position. In the far field, the wavefronts
become nearly parallel, and the intensity varies with range as squared by the inverse square law.
Within the far field, the beam is properly formed and the echo level can be predicted from the
standard equation.
[0019]
It can be seen from FIG. 5 that the smartphone speaker has poor response 506 in the low
frequency region. The peak is also seen at about 6 kHz. Regardless of these deficiencies,
smartphone speakers may still be considered for the reasons described below.
[0020]
a) Smartphone speakers have limited frequency response but can render signals above about
600 Hz (see also FIG. 6).
[0021]
b) If the smartphone speaker itself is used to render the measurement stimulus, the end user
does not have to have additional objects, such as balloons, for the measurement.
[0022]
c) Swept sinusoidal stimulation is easily implemented on smartphones as it has been proven and
widely used by many manufacturers and researchers.
[0023]
d) The user can move the smartphone (speaker) to any position around his / her head.
This allows flexible measurement of BRIR with any combination of orientation and height.
[0024]
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An example smartphone speaker amplitude response 601 generated by short range
measurements is shown in FIG.
From the figure, it can be seen that the spectrum has uniform characteristics starting from about
700 Hz.
Also shown is a “flat” objective function 602 and an exemplary inverse filter function 603 that
can be applied to fit the amplitude response 601 to the objective function 602.
[0025]
Two exemplary algorithms of BRIR calculation are described below. The BRIR resulting from the
headphone real room (HRR) process can be used to listen to the user's favorite content via the
headphones, including measured room information. The BRIR resulting from the headphone
virtual room (HVR) process can be used to listen to the user's favorite content via the
headphones, including only binaural information. However, the user can optionally include a
virtual room in the signal chain.
[0026]
The HRR system and method is intended to render binaural content, including information of the
room of the listener via headphones (earphones). A flowchart of an exemplary application of
BRIR measurements to an HRR system that includes a smartphone 701 is shown in FIG. 7 and
described in more detail below. Building blocks and procedures are also briefly described below.
[0027]
The BRIR measurement is performed by using a smartphone speaker 702 and placing a binaural
microphone (not shown) at the entrance of the user's ear canal. The swept sinusoidal signal for
spectral analysis is regenerated via the smartphone speaker 702 at the desired azimuth and
elevation. A pair of binaural microphones specially designed to completely plug the listener's ear
canal may be used. The microphone may be a separate set of binaural microphones, and the
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measurement hardware may be separate from the smartphone 701, similar to the system shown
in FIG. Alternatively, the earphone converter itself may be used as a transducer to capture sound.
The BRIR measurement, preprocessing and final calculation may be performed by the
smartphone 701, for example, using the mobile application performing the process described
above with respect to FIG. Broadband spectrum analysis, such as a fast Fourier transform (FFT)
or a filter bank, instead of a broad spectrum stimulus or impulse, instead of a spectral analysis by
frequency (e.g. swept narrowband stimulation associated with corresponding narrow band
analysis as described above) May be used in conjunction with
[0028]
For correction of smartphone speaker defects, a full bandwidth loudspeaker is ideally needed to
cover the full frequency range while measuring BRIR. Since a band-limited speaker, ie a
smartphone speaker 701, is used for the measurement, it is necessary to cover the missing
frequency range. To this end, short range measurements are obtained using one of the binaural
microphones. From here, as shown in FIG. 5, the inverse filter is calculated using exemplary
amplitude frequency characteristics (also known as "frequency characteristics" or "frequency
response") to the BRIR measurements of the left and right ears. Apply In the given example, the
target amplitude frequency response curve is set flat, but may be any desired curve. Information
such as phase difference and level difference is not corrected by this method, but may be
corrected as necessary. A flow chart of this process is shown in FIG. The process includes short
range measurement of the amplitude frequency response of the smartphone speaker 702
(procedure 801). The corresponding transfer function (also known as "transfer characteristic") of
the acoustic path between the smartphone speaker 702 and the microphone performing the
measurement is calculated (procedure 802) and added to the inverse target amplitude frequency
function 803 (procedure 804) . The (linear) finite impulse response (FIR) filter coefficients are
then calculated (procedure 805) and processed to perform a linear phase to minimum phase
transformation (procedure 806). After the filter coefficients performed in procedure 806 are
then reduced in length (procedure 807), the reduced-length filter coefficients are output
(procedure 808). A comparison of the results after applying the correction is shown in FIG. In
FIG. 9, a graph 901 shows amplitude frequency characteristics measured before equalization, a
graph 902 shows amplitude frequency characteristics measured after equalization, and a graph
903 shows amplitude frequency characteristics used for equalization. Show.
[0029]
For the (optional) spectrum balancer, additional equalization can be applied if the user wants to
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embed certain tones in the sound. For this purpose, the average value of BRIR of the left ear and
the right ear is acquired. A flow chart of the process is shown in FIG. The process provides the
body transfer function BRTF L of the left ear (procedure 1001), determines the binaural transfer
function BRTF R of the right ear (procedure 1002), smoothing (eg low pass filtering) (procedure)
1003 and 1004) and summing the smoothed binaural transfer functions BRTF L and BRTF R
(procedure 1005). Using the sum given by procedure 1005 and target amplitude frequency
response 1007, the filter coefficients of the corresponding inverse filter are then calculated
(procedure 1006). The filter coefficients are output in procedure 1008.
[0030]
With regard to headphone equalizers, even at the same manufacturer, sometimes there is a large
variation in the frequency response of the earphones, so the application of an equalizer is
required to correct for the effects from the earphones. To do this, the frequency response of the
individual earphones is required. This measurement of the earphone characteristics can be
performed using a simple device, as shown in FIG. The device for measuring earphone properties
comprises a tubular body (referred to herein as "tube 1101"). At one end of the body part is an
adapter 1102 for coupling the (in-ear) earphone 1103 to the tube 1101 and at the other end a
closing cap 1104 and a microphone 1105 arranged in the tube 1101 close to the cap 1104 and
Equipped with In practice, one of the binaural microphones may be used instead of the
microphone 1105 shown in FIG. The tube 1101 may have a reduced diameter portion 1006
somewhere between the two ends. The volume, length and diameter of the tube 1101 should be
similar to the average human ear canal. Because the illustrated device can mimic pressure
chamber effects, the measured response can be close to reality.
[0031]
The outline of the corresponding measurement process is shown in FIG. The process includes
measuring earphone characteristics (procedure 1201) and calculating a corresponding transfer
function from the measurements (procedure 1202). Further, at procedure 1204, the target
transfer function 1203 is subtracted from the transfer function obtained by procedure 1202.
From this sum, FIR coefficients are calculated (linearly) (procedure 1205) followed by a linear
phase to minimum phase transformation (procedure 1206) and a length reduction (procedure
1207). Finally, filter coefficients 1208 are output to other applications and / or systems.
[0032]
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Referring back to FIG. 7, the illustrated process includes a near-field measurement of the
amplitude frequency response of the mobile device's speaker, here the smartphone speaker 702
(procedure 703). The amplitude frequency response of the smartphone speaker 702 is calculated
from the signal by the procedure 703 (procedure 704). Next, an inverse filter amplitude
frequency response is calculated from the target amplitude frequency response 706 and the
calculated amplitude frequency response of the smartphone speaker 702 (procedure 705). After
the BRIR measurement is started and executed using the smartphone speaker 702 (procedure
707), the measured BRIR and the calculated inverse filter amplitude frequency response are
convoluted (procedure 708). The signal resulting from procedure 708 is processed by the room
equalizer based on the corresponding target frequency response 710 (procedure 709). The
signal according to procedure 709 is processed by the earphone equalizer based on the
corresponding target frequency response 712 (procedure 711). The signal according to
procedure 711 is convoluted with N monaural audio files 714 (eg N = 2 stereo signals, N = 6 5.1
channel signals or N = 8 7.1 channel signals) (procedure 713), The result of the convolution is
output to the earphone (procedure 715).
[0033]
The headphone virtual room (HVR) system is intended for rendering of binaural content without
including the information of the listener's room through the earphones. The listener can
optionally include a virtual room in the chain. An outline of the process is shown in FIG.
Additional building blocks are briefly described below. This process also requires the building
blocks described above in connection with FIGS. 7-12. Only additional building blocks such as
dereverberation devices and artificial reverberation devices are described below.
[0034]
Dereverberation / Smoothing: If the measured room impulse response contains unwanted peaks
or valleys, unpleasant acoustic artifacts can degrade the sound quality. A (time and / or
spectrum) window function technique can be incorporated to remove room information or to
remove early reflections and late reflections. In application, a combination of a rectangular
window and a Blackman Harris window is used as shown in FIG. An exemplary BRIR before
(1501) and after (1502) smoothing is shown in FIG.
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[0035]
Artificial Reverberation Equipment: In the previous block, all room related information was
removed. That is, after application of the window function (window), only direct information (for
example, interaural time difference [ITD] and interaural level difference [ILD]) is included in BRIR.
Thus, it seems that there is a sound source in the immediate vicinity of the ear. Thus, if it is
necessary to incorporate distance information, an artificial reverberator may optionally be used.
Any state of the art reverberator can be used for this purpose.
[0036]
As can be seen from FIG. 13, a dereverberation procedure 1301 and an artificial reverberation
procedure 1302 are inserted between the BRIR measurement process 707 and the earphone
equalization procedure 711 of the process shown in FIG. Furthermore, the room equalization
procedure 709 and the corresponding target amplitude frequency response 710 may be replaced
with a spectrum balancing procedure 1303 and a corresponding target amplitude frequency
response 1304. A dereverberation procedure 1301, which may include multiplying a window
function with a given window, and a convolution procedure 708 receive the output of the inverse
filter calculation procedure 705, and the convolution procedure 708 convolves with the
earphone equalization procedure 711. It may be performed between procedure 713.
[0037]
Throughout this study, the focus is not to break the phase information of BRIR. 17 provides the
amplitude frequency response of FIG. 16 of an exemplary BRIR and the phase frequency
response of FIG. The amplitude frequency response shows that the sharp peaks and valleys of the
BRIR have been removed after application of the dereverberation algorithm. The phase response
shows that even after dereverberation, the phase information is well preserved. In informal
listening, it was found that the localization of the convoluted speech was not destroyed either. In
FIG. 16, a graph 1601 shows an amplitude frequency response after earphone equalization, a
graph 1602 shows an amplitude frequency response after room equalization, a graph 1603
shows an amplitude frequency response after dereverberation, and a graph 1604. Shows an
amplitude frequency response after smartphone defect correction. In FIG. 17, a graph 1701
shows a phase frequency response after earphone equalization, a graph 1702 shows a phase
frequency response after room equalization, and a graph 1703 shows a phase frequency
response after dereverberation, a graph 1704 Shows the phase frequency response after
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smartphone defect correction.
[0038]
FIG. 18 shows the amplitude frequency response of an exemplary earphone transducer as a
microphone. As the system described herein may be targeted to consumer users, the earphone
converter and housing may be used in particular as a microphone. In the pilot experiments,
commercially available in-ear earphones were used as microphones to obtain measurements. A
swept sine wave signal ranging from 2 Hz to 20 kHz was reproduced through a speaker in the
anechoic chamber. The earphone capsule was about 1 meter away from the speaker. Reference
measurements were obtained using a reference measurement system for comparison. The
amplitude frequency response of the measured value is shown in FIG. In FIG. 18, a graph 1801
shows the amplitude frequency response of the left channel (1801), the right channel (1802),
and the reference measurement (1803). It can be seen from the plot that the shape of the curve
corresponding to the earphone is similar to the curve of the reference measurement of about
1,000 Hz to 9,000 Hz.
[0039]
While various embodiments of the invention have been described, it will be apparent to those
skilled in the art that many more embodiments and implementations are possible within the
scope of the invention. Accordingly, the invention is not to be restricted except in light of the
attached claims and their equivalents.
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