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JP2006171347

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DESCRIPTION JP2006171347
PROBLEM TO BE SOLVED: To improve reproduction characteristics of a small volume signal from
a speaker in accordance with the characteristics of a speaker actually installed. SOLUTION: When
performing correction processing for outputting an input audio signal from a speaker device
having a predetermined input / output characteristic, an audio signal as a reference is inputted to
the speaker device, and an output by the reference audio signal is a microphone The audio signal
obtained by the microphone is compared with the reference audio signal to analyze the amount
of decrease in sensitivity for each level, and the signal component of the level at which the
analyzed sensitivity of the audio signal supplied to the speaker device decreases. On the other
hand, correction processing to compensate for the decrease in sensitivity was performed.
[Selected figure] Figure 1
Audio signal processing method and audio reproduction system
[0001]
The present invention relates to an audio signal processing method for performing characteristic
correction in the case of reproducing an audio signal from a speaker device and an audio
reproduction system for performing the characteristic correction, particularly using a speaker
device for high fidelity reproduction capable of reproducing high sound quality. The present
invention relates to a technique suitable for application.
[0002]
Conventionally, various configurations have been put to practical use as speaker devices for high
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fidelity reproduction capable of high-quality sound reproduction.
For example, there is a three-way speaker device in which a reproduction band of an audio signal
is divided into three bands of low, middle, and high bands, and separate speaker units are
prepared for each band. This 3-way speaker device can reproduce the input audio signal
faithfully from the low band to the high band by using a speaker unit for each band that has
good reproduction characteristics in each band. Generally, the reproduction characteristic is
better than that of a so-called full range type speaker unit in which audio of all bands is output
by one speaker unit.
[0003]
Further, in addition to the configuration for enhancing the reproduced sound of the speaker
device such as the 3-way configuration and the 2-way configuration as described above, the
characteristic of the audio signal itself supplied to the speaker device is It is also performed to
correct on the device side to improve the characteristics of the audio output from the speaker
device as a result. For example, an audio amplifier device that performs processing such as
amplification of an audio signal that drives a speaker device may perform correction called
loudness control. This loudness control performs correction processing that enhances the output
level compared to the midrange part with the bass part and the trebleband part, and corrects that
the low band and the high band are heard mainly when the volume is small. It is a thing.
[0004]
Patent Document 1 describes an example of a reproduction configuration when loudness
correction is performed. JP 2002-171589 A
[0005]
However, since the loudness-controlled playback sound simply boosts the signal of a specific
frequency band almost uniformly regardless of the level, it is not strictly a reproduction that is
faithful to the input audio signal, but rather the input audio. It has been desired to develop a
reproduction system capable of reproduction faithful to the signal. That is, since the conventional
loudness-controlled reproduction sound is reproduced by enhancing the sound which is hard to
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hear when the volume is small, the bass and treble parts become easier to hear compared to the
reproduction sound without the loudness control, and the sound quality to some extent Although
it is effective to improve the signal of a specific frequency band even if it is a small level or a
large level, it is possible to enhance also the signal component which does not need to be
enhanced. In some cases, the result may be an unnatural reproduced sound.
[0006]
Here, to explain the problem of the reproduced sound in the conventional speaker device, there
is a problem of a small amplitude signal as an example in the case where the reproduced sound
does not faithfully reproduce the input audio signal. That is, for example, as shown in FIG. 9A, it
is assumed that an input audio signal S1 having a waveform in which a waveform having a
relatively large amplitude and a waveform having a relatively small amplitude are continuous is
input to the speaker. At this time, the waveform of the output audio signal S2 from the speaker is
substantially the same as the input signal S1 for the waveform of relatively large amplitude, but
the amplitude of the waveform of relatively small amplitude is higher than that of the input
signal S1. It tends to be smaller. This is because a speaker unit having a general diaphragm
capable of outputting a relatively loud sound has poor reproduction characteristics of a small
volume signal with a small amplitude, and the linearity of the input / output characteristics of the
small volume signal ( Linearity) is not ensured.
[0007]
Similarly, for example, as shown in FIG. 9 (b), the input audio signal S3 of a waveform of
relatively large amplitude and the input audio signal S4 of a waveform of relatively small
amplitude overlap in time, so that they are inherently The audio signal S5 obtained by combining
the two signals S3 and S4 is output, but the output audio signal S6 having a waveform whose
level is lower than the waveform of the combined signal S5 is output from the speaker. For
example, when the sounds of various instruments are simultaneously reproduced as the audio to
be reproduced from the speaker, such as symphony, such an output state may occur.
[0008]
Further, for example, as shown in FIG. 9C, when there is an impulse signal in which the amplitude
of the signal of a specific single frequency gradually decreases as the input audio signal S7, the
waveform of the output audio signal S8 from the speaker Also, as the level decreases, the
followability deteriorates.
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[0009]
In any of the examples shown in FIG. 9, the output level of the small volume signal having a small
amplitude becomes smaller than the input signal level as the output from the speaker, and the
linearity of the small signal is not maintained.
When frequency analysis is performed on the state shown in FIG. 9, for example, the state shown
in FIG. The example of FIG. 10 is an example in which the sensitivities of the fundamental wave
f1 and the harmonics f2 and f3 that are harmonics of the fundamental wave are analyzed. The
fundamental wave f1 with a high level is output as it is, but the harmonics f2 and f3 whose levels
are smaller than the fundamental wave have output sensitivities shown by a solid line that is
lower than the original level shown by a broken line. ing.
[0010]
FIG. 11 is a diagram showing output characteristics from low to high frequencies at multiple
levels of signal levels, and FIG. 11 (a) is an ideal characteristic, and FIG. 11 (b) is an actual
speaker output It is the figure which showed the characteristic. As shown in FIG. 11A, in an ideal
state, it is assumed that the four levels L1, L2, L3, and L4 have flat characteristics from low to
high frequencies at substantially equal intervals. At this time, as the actual output characteristics
of the speaker shown in FIG. 11B, output characteristics substantially equivalent to the ideal
characteristics can be secured for the levels L1, L2, and L3 having high output levels, but the
lowest level The characteristic of L4 is a level which is lowered in any frequency band by the
sensitivity α from the originally necessary level.
[0011]
It is an input / output characteristic diagram of FIG. 12 that such a decrease in sensitivity is
viewed as a characteristic of a specific frequency. As shown in FIG. 12, the characteristic x of the
broken line in which the output level increases linearly with the increase of the input signal level
to the speaker has to be originally required, but in fact it is a certain level or more In this case,
the level changes almost linearly, but below a specific level, the movement of the diaphragm with
respect to the input is bad, and the output sensitivity to the input has a characteristic y of a curve
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that is very bad.
[0012]
Specifically, for example, assuming that the maximum level of listening by a general speaker is
70 to 100 spl (sound pressure level), a signal which is -30 dB to -60 dB lower than the maximum
level is correct for the maximum level- It means that the volume lowered by 30 dB to -60 dB is
not output (not proportional). Assuming that the volume of the output of the amplifier device is
reduced by 50 spl from 100 spl, the volume at around 50 spl should be obtained originally, but
in practice only 40 spl whose output is 10 spl lower is actually obtained, for example. It will not
be possible. That is, it means that linearity can not be accurately obtained, and it has been found
by analysis of the present inventor that it is one of the major causes for not obtaining satisfactory
sound quality.
[0013]
By the way, the curve state of the curve of the characteristic y shown in FIG. 12 described above
is an example, and in fact, the specific curve state of the characteristic y changes depending on
the characteristics of the individual speaker devices. I will. That is, the input / output
characteristics of the speaker device are determined by the conditions such as the size and
weight of the vibration system of the speaker unit included in the speaker device, and may vary
depending on the installation environment of the speaker device. It was difficult to decide the
[0014]
The present invention has been made in view of the foregoing, and it is an object of the present
invention to improve reproduction characteristics of a relatively small volume signal from a
speaker.
[0015]
The present invention inputs an audio signal as a reference to the speaker device when
performing correction processing for outputting the input audio signal from the speaker device
having a predetermined input / output characteristic, and outputs an output of the reference
audio signal as a microphone The audio signal obtained by the microphone is compared with the
reference audio signal to analyze the amount of decrease in sensitivity for each level, and the
signal component of the level at which the analyzed sensitivity of the audio signal supplied to the
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speaker device decreases. On the other hand, correction processing is performed to compensate
for the decrease in sensitivity.
[0016]
By doing this, as an audio signal output from the speaker device, an input / output characteristic
in which an insufficient amount of sensitivity is corrected according to the characteristics of the
speaker device becomes an almost linear audio signal, and in particular, the output is originally A
relatively low level signal whose level is insufficient will be output well at the original level.
[0017]
According to the present invention, since the audio actually output from the speaker device is
analyzed, the sensitivity to be corrected can be set optimally in accordance with the speaker
device, and the correction is made in accordance with the characteristics of the connected
speaker device. An audio signal having substantially linear input / output characteristics can be
output, and in particular, a relatively low level signal which originally lacks an output level can be
output well at the original level.
[0018]
In this case, as the correction processing, the reproduction characteristic can be improved in all
frequency bands by performing correction processing that compensates for the decrease in
output sensitivity substantially uniformly for each level within substantially all frequency bands
output by the speaker device. It is possible to reproduce with high fidelity to the input audio
signal, which is completely different from the conventional enhancement of only a specific band
such as loudness control.
[0019]
Further, by providing the storage means for storing the amount of decrease in sensitivity for each
level analyzed by the analysis means, for example, when installing the reproduction system, the
output audio of the speaker device is analyzed and stored using the microphone only once. Then,
after that, it is possible to perform the optimum correction using the stored data.
[0020]
Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1
to 8.
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FIG. 1 is a diagram showing an example of a system configuration according to the present
embodiment.
In this example, the audio reproduction system to which the speaker device is connected is set as
an example installed in a vehicle such as a car, and FIG. 1 is a view showing an example of the
entire system configuration.
In this example, the audio signal source 10 is connected to the amplifier device 20, and the audio
signal source 10 reproduces an audio signal recorded (stored) in a medium such as a CD (disc) or
memory, and reproduces the audio signal. The audio signal to be output is supplied to the
amplifier device 20, and the amplifier device 20 performs processing to convert the audio signal
into an audio signal for driving the speaker device.
It may be an audio signal received and input by a tuner (not shown) or the like.
Details of the specific processing state in the amplifier device 20 will be described later.
[0021]
Here, as shown in FIG. 1, a plurality of speaker devices 31, 32, 33, 34 are disposed at
predetermined positions in the vehicle.
Specifically, for example, the speaker devices 31 and 32 are disposed on the left and right in the
front of the vehicle, and the speaker devices 33 and 34 are disposed on the left and right in the
rear.
[0022]
The audio signal output from the audio signal source 10 is a signal of at least two channels of an
audio signal for the left channel and an audio signal for the right channel. For example, the audio
signal for the left channel output from the amplifier device 20 is the left channel The right
channel audio signal is supplied to the right channel speaker devices 32 and 34 for output.
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[0023]
The configuration of each of the speaker devices 31, 32, 33, 34 will be described. Each of the
speaker devices 31 to 34 includes one speaker unit as a speaker unit as sound output means for
outputting audio.
Each of the speaker units is a so-called full-flare type speaker unit having a characteristic that is
substantially flat in the audible band and that is outputted from the low band to the high band as
a characteristic viewed from the output frequency band The speaker unit has a relatively large
diaphragm and can output a high volume signal as a relatively large speaker unit. In the speaker
unit of this example, since the diaphragm is relatively large, the linearity of the input / output
characteristics of a large signal above a predetermined level can be substantially maintained, and
the input / output characteristics below the predetermined level Of the output signal level is
inferior to the input signal level. That is, the speaker unit having the characteristic y described
with reference to FIG. 12 in the background art section is used. A speaker unit having such
characteristics is general as a speaker.
[0024]
In this example, in the audio reproduction system to which the speaker devices 31 to 34 using
the speaker unit having such characteristics are connected, the signal is processed by the
amplifier device 20 processing the audio signal supplied to the speaker devices 31 to 34. It is
intended to perform the characteristic correction of
[0025]
FIG. 2 is a diagram showing the configuration of the amplifier device 20 of this example.
As shown in FIG. 2, an audio signal obtained at the audio signal input terminal 21 of the amplifier
device is supplied to an analog / digital converter 22, converted into a digital audio signal, and
the converted digital audio signal is Supply to the signal processor 23 In this example, this DSP
23 is used as a means for correcting audio signal characteristics. The correction state of the DSP
23 is set under the control of the control unit 26. A memory 27 for storing data necessary for
control is connected to the control unit 26, and data on the correction state in the DSP 23 is also
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stored. In addition, a reference audio signal necessary for analysis to be described later is also
stored in the memory 27, and instead of the input audio signal, the reference audio signal can be
supplied to the speaker side and output.
[0026]
As correction processing in the DSP 23, for example, signal components of all frequency bands in
digital operation processing are divided into signal components of a predetermined level or more
and signal components of a predetermined level or less, and nothing is performed on signal
components of a predetermined level or more Do not perform correction processing. Then, for
signal components less than the predetermined level, correction processing is performed such
that the increase rate becomes higher as the output level becomes lower than the input level.
Here, in the present embodiment, the correction processing state can be variably set by the
control of the control unit 26. In the correction processing in the case of this example, the
optimum correction state is automatically set based on the actually measured reproduction state,
but the correction state can be adjusted by the user's key operation or the like. It is also good.
Details of the correction state will be described later.
[0027]
Then, the signal component above the predetermined level not subjected to the correction
process and the signal component below the predetermined level subjected to the correction
process are synthesized, and the synthesized signal is supplied to the digital / analog converter
24 to be an analog audio signal. Convert.
[0028]
The converted analog audio signal is supplied to an amplifier 25 to be amplified for driving a
speaker, and the amplified audio signal is supplied to each of the speaker devices 31 to 34 to
output (discharge) an audio signal.
[0029]
As the control of the correction process by the DSP 23 by the control unit 26, in the case of this
example, the control based on the analysis result of the audio signal picked up by the
microphone 42 is performed.
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That is, in the present example, the microphone 42 is connected to the system, and the
microphone 42 is arranged to pick up the audio output from the speaker devices 31 to 34.
The microphone 42 may be connected only when necessary as a detachable configuration. The
audio signal obtained by the microphone 42 is supplied to the analog / digital converter 29
through the buffer amplifier 41 to be converted into a digital audio signal, and the converted
digital audio signal is supplied to the analysis unit 28. The analysis unit 28 analyzes the supplied
audio signal.
[0030]
As the audio signal analysis in the analysis unit 28, the audio signal obtained by the microphone
42 is compared with the reference audio signal prepared in advance to analyze the amount of
decrease in sensitivity for each level. The sensitivity drop analyzed in this example is less
dependent on the frequency (that is, less change depending on the frequency) as described later,
so it may be possible to analyze only a signal of a specific frequency. You may analyze finely for
every zone. Thus, the input / output characteristics of the speaker devices 31 to 34 connected to
the system can be analyzed by comparing the reference audio signal with the audio signal picked
up by the microphone.
[0031]
Then, the control unit 26 determines the analysis result of the speaker device and causes the DSP
23 to execute correction processing so as to correct the decrease in the output sensitivity of the
speaker device at a predetermined level or less of the sensitivity to the input. The data of the
correction state based on the analysis result is stored in the memory 27 and, for example, is
stored until the value of the correction state is updated.
[0032]
To explain an example of analysis of an audio signal by the analysis unit 28, for example, it is
assumed that an impulse signal shown as a waveform w0 in FIG. 3 is supplied from the amplifier
device 20 to a speaker device as a reference audio signal. At this time, the audio signal waveform
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picked up by the microphone 42 is, for example, the waveform w1 shown in FIG. 3, and when the
level drops below the predetermined level as compared with the waveform w0, the sensitivity
drops significantly. At this time, analysis is conducted to determine what level of sensitivity
reduction occurs below which level.
[0033]
FIG. 4 shows an example of an analysis state when the fundamental wave of the specific
frequency f1 and its overtones f2, f3... Are reproduced. As for the fundamental wave, since the
level is high, an output level corresponding to the input level is detected, but for example, a
signal component of the frequency f2 having twice the frequency is detected to be lower than the
original level by the sensitivity d1. Similarly, for example, the signal component of the frequency
f3 having triple frequency is detected to be reduced by the sensitivity d2 than the original level.
[0034]
Such a decrease in sensitivity is detected and analyzed, and correction processing for
compensating for the decrease in sensitivity is performed on the signal component at a level at
which the analyzed sensitivity is reduced, and the signal is output from the speaker devices 31 to
34. The audio signal is a good reproduced sound that is faithful to the input audio signal.
[0035]
FIG. 5 is a diagram showing a state in which an audio signal is output from the speaker devices
31 to 34 by correction with such characteristics as an output characteristic from low to high
frequencies at multiple levels of signal levels.
FIG. 5A is a diagram showing the output characteristics (i.e., the uncorrected output
characteristics) of the speaker devices 31 to 34 of this example. FIG. 5A is the same as the
speaker characteristic shown in FIG. 11B as the background art. That is, as shown in FIG. 5A, for
the levels L1, L2 and L3 having high output levels, an output characteristic substantially
equivalent to the ideal characteristic can be secured, but for the output characteristic at the
lowest level L4, The level is lowered in any frequency band by the sensitivity α from the
originally necessary level.
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[0036]
Here, as shown in FIG. 5B, the output characteristics of the signal input to the amplifier device 20
by performing the correction in the amplifier device 20 include the levels L1, L2, and L3 having
high output levels. Although there is no change with the input level, the output characteristic of
the lowest level L4 is a level which rises from the original level by the sensitivity β and in any
frequency band. Here, the increased sensitivity β is optimally set based on actual measurement
and analysis so as to substantially compensate for the sensitivity α that is lowered by the
speaker devices 31 to 34.
[0037]
With such characteristics, by causing the speaker devices 31 to 34 to output the audio signal
processed by the amplifier device 20, FIG. 5C shows audio characteristics to be output from the
speaker devices 31 to 34. As shown, the four levels L1, L2, L3, and L4 have flat characteristics
from low frequency to high frequency at substantially equal intervals, and are substantially equal
to the ideal characteristics shown in FIG. 11A. Is a good characteristic that matches regardless of
the level in all frequency bands.
[0038]
FIG. 6 is a diagram showing an example of characteristics corrected by the DSP 23 at a specific
frequency.
In FIG. 6, a characteristic a indicated by a broken line is a characteristic in which the linearity is
linearly proportional to the increase and decrease of the input level and the increase and
decrease of the output level, and is shown for reference. The characteristics b, c and d shown by
solid lines are examples of three characteristics corrected by the DSP 23 of this example.
[0039]
As shown by the characteristics b, c and d, the correction characteristics in the DSP 23 of this
example are characteristics in which the linearity is taken such that the increase and decrease of
the input level and the increase and decrease of the output level are linearly proportional (Ie, a
characteristic that substantially matches the characteristic a) (ie, the input level and the output
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level are equal). And in the range below the predetermined level, the characteristic indicated by
the curve where the increase rate becomes high compared to the linear input / output
characteristic a as the level is lower with respect to the input level It is made to become.
[0040]
Here, in the present example, since the characteristic of the curve is obtained based on the result
of analysis from the reproduced sound from the speaker device, any one of the characteristics b,
c and d, for example, is selected. Alternatively, when the curve obtained from the analysis result
is different from the characteristics b, c, d, another characteristic is set. Note that the
characteristics b, c and d shown in FIG. 6 show the characteristics at a specific frequency, but in
the case of this example, they are substantially the same in all audible bands reproducible by the
speaker. It is made to have a characteristic. Further, the correction curve obtained from the
analysis result may be adjusted to some extent by the user operation. As adjustment by user
operation, for example, when the adjustment amount is 0, the curve obtained from the analysis
result is set as it is as a correction curve, and when adjusted in the + direction, the correction
curve is made a tighter curve. When adjusting in the-direction, it is conceivable to make the
correction curve a curve with a slower curve.
[0041]
Next, the processing procedure for setting the correction state by analyzing the audio signal
input from the microphone 42 connected to the amplifier device 20 of this embodiment will be
described with reference to the flowchart of FIG. First, an audio signal serving as a reference for
measurement prepared in the memory 27 or the like is output from the speaker device (step
ST11). The output audio signal is input by the microphone 42, digitized, and taken into the
analysis unit 28 (step ST12). Then, the captured audio data is compared with the reference audio
data to analyze the reduction in sensitivity for each level (step ST13). Based on the analyzed
result, the control unit 26 calculates the sensitivity correction amount of the low level signal
(step ST14), stores the calculated correction amount in the memory 27 (step ST15), and
performs the setting operation of the correction state. Finish.
[0042]
Next, an example of processing when outputting (reproducing) an audio signal supplied from the
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audio signal source 10 using data of the correction state set in this way will be described with
reference to the flowchart of FIG. Do. First, when the reproduction system is powered on (step
ST21), the control unit 26 reads the data of the correction amount stored in the memory 27 and
causes the DSP 23 to set the correction amount (step ST22). Then, the control unit 26 determines
whether or not there is an operation of adjusting the correction state by the user operation (step
ST23). Here, when it is determined that there is an operation to adjust the correction state, the
correction amount set in the DSP 23 is changed (corrected) based on which adjustment operation
(step ST24). Then, the stored data of the memory 27 is updated with the changed correction
amount (step ST25).
[0043]
By correcting the reproduction characteristic from the speaker device in this manner, the audio
signal input from the audio signal source 10 or the like is output with a faithful characteristic,
and the reproduction sound quality can be improved. Such reproduction characteristics faithfully
reproduce the input audio signal, which is completely different from the processing of enhancing
the signal of a specific frequency band regardless of the level, such as the conventionally known
loudness control. It is a characteristic.
[0044]
Moreover, in the case of this example, since the correction is performed based on the result of
picking up and analyzing the sound actually output from the speaker device, unlike the case
where the correction characteristic is prepared in advance, Correct even if there is variation. In
addition, although there may be differences in input / output characteristics depending on the
installation environment of the speaker device, such differences can be dealt with. In particular,
when installed in a car as a car stereo as in the installation example shown in FIG. 1, for example,
the reproduction environment may be completely different depending on the type of car to be
installed and the installation position of the speaker device. Automatic correction as in the
example is very effective.
[0045]
The reproduction system of this embodiment is applicable to various audio reproduction systems,
and in the example shown in FIG. 1, the audio signal source 10, the amplifier device 20, and the
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speaker devices 31 to 34 are separately configured. However, it may be an integrated system
(device). Alternatively, a correction means for correcting the characteristics of the single speaker
device may be incorporated in a single speaker device, and may be connected to an amplifier
device having no correction processing function. Alternatively, the same correction may be
applied to the audio signal itself output from the audio signal source 10.
[0046]
Further, although in the above-described embodiment the reproduction system for car stereo is
used, it can be applied to various audio reproduction systems such as a general indoor
reproduction system. Even in the case of a reproduction system for a car stereo, the number of
connected speaker devices is not limited to the above-described example.
[0047]
In the above-described embodiment, the analysis from the speaker device is performed in
advance using the audio signal as a reference, and the calculated correction characteristic is set.
For example, the reproduced sound from the speaker device Is it necessary to always connect a
microphone that picks up the input audio signal to the amplifier device at the time of actually
reproducing the audio signal with the output sound from the speaker device and correct the
correction amount? The amount of correction may be corrected at any time by monitoring. In
such a case, it is possible to properly adjust the correction amount only from the actual
reproduction situation without preparing a reference audio signal for initially setting the
correction amount.
[0048]
Further, in the above-described embodiment, the correction characteristics are calculated and set
at one time on the assumption that the reproduction characteristics of a plurality of prepared
speaker devices are equal, but, for example, one reference audio signal is used. Two speaker
devices are individually output and analyzed individually based on the reproduced sound of each
speaker device, and different correction characteristics are set for each one speaker device based
on the individually analyzed results You may make it By doing this, the reproduction
characteristics of each one of the speaker devices are strictly corrected, and better reproduction
characteristics can be obtained.
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[0049]
It is a block diagram showing an example of system composition by one embodiment of the
present invention. It is a block diagram showing an example of composition by a 1 embodiment
of the present invention. It is the wave form diagram which showed the example of a
characteristic of the speaker apparatus by one embodiment of the present invention. It is a
characteristic view showing an example of measurement of a characteristic of a speaker device
by one embodiment of the present invention. It is the characteristic view which showed the
example of the correction ¦ amendment state by one embodiment of this invention by output
sensitivity for every frequency. FIG. 6 is a characteristic diagram showing an example of
correction characteristics according to an embodiment of the present invention. It is the flow
chart which showed the example of setup of the amendment amount by one embodiment of the
present invention. It is the flowchart which showed the processing example at the time of the
audio output by one embodiment of this invention. It is explanatory drawing which showed the
example of an output waveform of the conventional speaker. It is explanatory drawing which
showed the example of the signal level of the conventional speaker. It is explanatory drawing
which showed the output characteristic example (a) of an ideal speaker, and the output
characteristic example (b) of the conventional speaker. It is explanatory drawing which showed
the example of the input-output characteristic of the conventional speaker.
Explanation of sign
[0050]
DESCRIPTION OF SYMBOLS 10 ... Audio signal source, 20 ... Amplifier apparatus, 21 ... Audio
signal input terminal, 22 ... Analog / digital converter, 23 ... DSP (digital signal processor), 24 ...
Digital / analog converter, 25 ... amplifier, 26 ... control unit, 27 ... memory, 28 ... analysis unit, 29
... analog / digital converter, 41 ... amplifier, 42 ... microphone
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