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JP2006174078

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DESCRIPTION JP2006174078
PROBLEM TO BE SOLVED: To make it possible to well correct a specific frequency band of an
audio signal. When correction processing is performed on a signal of a specific frequency band of
an input audio signal, the output level is substantially uniformly increased with respect to a
signal component below a predetermined level of the signal of the specific frequency band The
correction processing is performed so that the output level is not changed for signals outside the
specific frequency band. [Selected figure] Figure 3
Audio signal processing method and apparatus
[0001]
The present invention relates to an audio signal processing method and apparatus for performing
characteristic correction in the case of reproducing an audio signal, and more particularly to a
technology suitably applied to the case of using a speaker device for high fidelity reproduction
capable of reproducing high sound quality.
[0002]
Conventionally, various configurations have been put to practical use as speaker devices for high
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
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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
speaker device capable of faithful reproduction to a signal. That is, since the conventional
loudness-controlled reproduction sound is reproduced by enhancing the sound which is hard to
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.
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[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. 5A, 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. 5 (b), the input audio signal S3 having a relatively large
amplitude waveform and the input audio signal S4 having a relatively small amplitude waveform
overlap in time, so that, in principle, 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]
Furthermore, for example, as shown in FIG. 5C, 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.
[0009]
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In any of the examples shown in FIG. 5, the output level of the small volume signal having a small
amplitude is 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. 5, for example, the state shown
in FIG. 6 is obtained. The example of FIG. 6 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. 7 shows output characteristics from low to high frequencies at multiple levels of signal
levels. FIG. 7 (a) is an ideal characteristic, and FIG. 7 (b) is an output of an actual speaker. It is the
figure which showed the characteristic. As shown in FIG. 7A, in an ideal state, it is assumed that
the four levels L1, L2, L3, and L4 have flat characteristics from low to high regions at
substantially equal intervals. At this time, as the output characteristics of the actual speaker
shown in FIG. 7 (b), for the levels L1, L2 and L3 having high output levels, output characteristics
substantially equivalent to the ideal characteristics can be secured, 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. 8 that such a decrease in sensitivity is seen
as a characteristic of a specific frequency. As shown in FIG. 8, 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 that is
very bad.
[0012]
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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]
As one of the conventionally known processes for correcting such inferiority of reproduction
characteristics, for example, the loudness control described above is performed to set the output
levels of the bass region and the treble region to the midrange region. There is a process to make
it stronger than that. In addition, as another process, for example, using a device called graphic
equalizer, the level is increased or decreased for each of a plurality of divided frequency bands,
and the listener is adjusted to have a desired reproduction sound quality. It may be
[0014]
FIG. 9 is a diagram showing an example of correction characteristics when a conventional
graphic equalizer is used. When adjusting the gain of the audio signal with the graphic equalizer,
the adjuster selects a band for adjusting the gain, and increases or attenuates the level by
operating the gain setting operation knob for operating the band. Set That is, as shown in FIG. 9,
when a band FW to adjust the gain is selected, the level of all signal components in the band is
increased or decreased by the same operation by operating the gain setting operation knob for
that band. Become. Therefore, for example, if it is felt that the small signal in this band FW is
insufficient, the operation to increase the gain is performed, but as can be seen from FIG. 9, the
same amount of gain is obtained for the large signal in the same band. As a result, there is a
problem that the audio signal in the band FW becomes extremely conspicuous as compared with
the other bands and has a poorly balanced reproduced sound quality.
[0015]
The present invention has been made in view of the foregoing, and it is an object of the present
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invention to make it possible to well correct a specific frequency band of an audio signal.
[0016]
According to the present invention, when correction processing is performed on a signal of a
specific frequency band of an input audio signal, the output level is substantially uniformly raised
with respect to a signal component of a predetermined level or less of the signal of the specific
frequency band. The correction processing is performed so that the output level is not changed
for signals other than the specific frequency band.
[0017]
By doing this, by outputting the audio signal subjected to the correction processing, only the
level of the signal of a small amplitude below the predetermined level of the frequency band
where the signal is to be enhanced rises, and the amplitude is relatively large. Since the signal is
hardly changed, the reproduction sensitivity of the low level signal of the desired frequency band
can be improved without changing the overall signal level.
[0018]
According to the present invention, by outputting a corrected audio signal, only the level of a
small amplitude signal below a predetermined level of the frequency band where the signal is to
be enhanced is increased, and a signal with a relatively large amplitude above the predetermined
level Since the level hardly changes regardless of the band, the reproduction sensitivity of the
low level signal of the desired frequency band can be improved without changing the overall
signal level, and good audio reproduction is possible.
[0019]
In this case, as the input / output characteristic of the speaker device for outputting the
corrected audio signal, the predetermined level substantially secures the linearity of the output
level with respect to the input signal above the specific level, and the output level with respect to
the input signal is below the specific level. By being a specific level in the case of the
characteristic to be reduced, good signal correction can be performed in accordance with the
characteristic of the speaker device.
[0020]
Further, by variably setting the specific frequency band based on the operation input, it is
possible to perform signal correction of an arbitrary frequency band.
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[0021]
Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1
to 4.
FIG. 1 is a diagram showing an example of a system configuration according to the present
embodiment.
The present embodiment is an audio reproduction system connected with a speaker device, and
FIG. 1 is a diagram showing an example of the entire system configuration.
In this example, the audio signal source 10 is connected to the amplifier device 20 through the
graphic equalizer 100, and the audio signal source 10 reproduces an audio signal recorded
(stored) in a medium such as a CD (disk) or memory. The audio signal to be reproduced and
output is processed by the graphic equalizer 100 and then supplied to the amplifier device 20,
and the amplifier device 20 performs processing to generate an audio signal for driving the
speaker device.
[0022]
In the case of this example, the audio signal output from the audio signal source 10 is a signal of
two channels of an audio signal for the left channel and an audio signal for the right channel.
The left channel audio signal output from the amplifier device 20 is supplied to the left channel
speaker device 30L for output, and the right channel audio signal is supplied to the right channel
speaker device 30R for output.
[0023]
The left-channel speaker device 30L and the right-channel speaker device 30R basically have the
same configuration (however, the outer shape may be slightly different, for example, they may be
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laterally symmetrical).
In the following description, the left and right channel speaker devices 30L and 30R may be
referred to as the speaker devices 30 attached with the same symbols except for L and R when
the channels are not distinguished.
[0024]
The configuration of each of the speaker devices 30L and 30R will be described. Each of the
speaker devices 30L and 30R includes one speaker unit 31 (FIG. 2) as a speaker unit as sound
output means for outputting audio.
Each of the speaker units 31 is a so-called full-franking type speaker unit having a characteristic
that is substantially flat in the audible band as a characteristic seen from the output frequency
band and that is outputted from low to high frequencies There is a relatively large diaphragm
and a relatively large speaker unit capable of outputting a high volume signal. As for the speaker
unit 31, since the diaphragm is relatively large, the linearity (linearity) of the input / output
characteristics of large signals above a predetermined level is substantially maintained, and the
linearity of the input / output characteristics is not secured below the predetermined level. 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. 8 in the background art section is used. A
speaker unit having such characteristics is general as a speaker.
[0025]
In this example, in the audio reproduction system to which the speaker device 30 using the
speaker unit 31 having such characteristics is connected, the graphic connected to the front
stage of the amplifier device 20 processing the audio signal supplied to the speaker device 30
The equalizer 100 is designed to perform signal characteristic correction.
[0026]
FIG. 2 is a view showing a configuration example of the graphic equalizer 100 of this example.
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An audio signal obtained at the audio signal input terminal 101 of the graphic equalizer 100 is
supplied to an analog / digital converter 102 to be converted into a digital audio signal, and the
converted digital audio signal is converted into a DSP (digital signal processor) 110. Supply to
[0027]
The processing configuration in the DSP 110 is divided into signal components for each
frequency band for processing an audio signal by a plurality of band pass filters 111a to 111n (n
is an arbitrary integer of 2 or more), and each of the divided The signal components are supplied
to the variable dynamic range controllers 112a to 112n, and variable dynamic range control
processing is performed by digital arithmetic processing for each band. The adjustment amount
for performing the dynamic range control process in each band is set according to the operation
status of the operation unit (not shown). This variable dynamic range control processing is signal
processing which becomes a characteristic in the present embodiment, and the details will be
described later.
[0028]
Then, the signal components processed by the variable dynamic range controllers 112a to 112n
are supplied to the synthesizing unit 113 to be synthesized into one stream of audio data, and
the synthesized audio data is supplied to the digital / analog converter 103. Then, the audio
signal is converted into an analog audio signal, and the converted audio signal is supplied from
the audio signal output terminal 104 to a device at the subsequent stage (in the case of the
configuration of FIG. 1, the amplifier device 20). Although only the configuration for processing
an audio signal of one channel is shown in the configuration of FIG. 2, for example, when
processing an audio signal of two channels as shown in FIG. 1, the circuit shown in FIG. It has
two lines of configuration. The configuration shown in FIG. 2 is a configuration viewed from the
data processing function, and the filters 111a to 111n and the controllers 112a to 112n do not
necessarily have n processing units in the DSP.
[0029]
Next, the process example of the graphic equalizer 100 of this example will be described. For
example, as shown in FIG. 3, it is assumed that the frequency band FW of the input audio signal
is set by the operation of the operation unit to perform dynamic range control. . At this time, the
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variable dynamic range controller 112x (the controller 112x is one of the controllers 112a to
112n) that processes the output of the band pass filter 111x (the filter 111x is any one of the
filters 111a to 111n) that extracts the signal component of the band FW. Change the dynamic
range with any of the controllers). Although FIG. 3 illustrates an example in which only one band
FW is corrected, it is also possible to perform correction processing simultaneously in a plurality
of frequency bands among the bands divided and set by the filters 111a to 111n.
[0030]
As the change processing of the dynamic range here, as shown in FIG. 3, with respect to the
audio signal in the frequency band FW, the level is not changed for a large signal of a
predetermined level or more, and the level of a small signal of a predetermined level or less To
raise the The predetermined level is determined, for example, by the input / output
characteristics of the speaker units included in the connected speaker devices 30L and 30R.
Specifically, the boundary between the range in which the linearity (linearity) of the input /
output characteristics of the speaker unit is substantially maintained and the range in which the
linearity of the input / output characteristics is not ensured is made to substantially coincide with
a predetermined level. Also, as a characteristic to raise the level of the small signal below the
predetermined level, the characteristic shown by the curve is such that the lower the level, the
higher the increase rate compared to the characteristic where the input and output are equal.
The speaker unit works to correct the badness of the input / output characteristics of the speaker
unit.
[0031]
Specifically, as shown in FIG. 8 described in the background art section, as the input / output
characteristic of the speaker unit, the characteristic y is a characteristic y indicated by a curve in
which the linearity of the input / output characteristic is not secured below a predetermined
level. For example, as shown in FIG. 4, the audio signal having a predetermined level or less in
the frequency band FW has a characteristic b in which the input and output of the characteristic
y are substantially reversed. Note that the characteristic a shown in FIG. 4 is an ideal
characteristic in which the linearity of the input and output is secured for reference.
[0032]
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However, the adjustment amount to be the characteristic b shown in FIG. 4 may be used as the
reference adjustment amount, and the increase rate of the small signal may be adjusted by the
user operation based on the reference adjustment amount. Further, the value itself of the level
(the above-described predetermined level) serving as a boundary point for raising the level of the
small signal may be variably set.
[0033]
By performing the correction process of the dynamic range in such a correction, in the frequency
band in which the correction is performed, the poorness of the input / output linearity is
corrected, and the characteristic close to the ideal characteristic a Become. For example, by
performing the correction process of the dynamic range as shown in FIG. 3 with respect to the
high frequency band or the middle frequency band where signals of relatively small level are
easy to hear, the output characteristic from the connected speaker device 30 is excellent It
becomes a thing. In this case, since the reproduction level of the large level signal is not
corrected (enhanced) at any frequency band, dynamic range correction can be performed only
for the desired frequency band without disturbing the overall reproduction balance, and good
reproduction can be performed. Sound is obtained.
[0034]
Moreover, in the case of this example, since the dynamic range correction processing can be
performed for each frequency band divided and set by the graphic equalizer 100, the user can
adjust while actually listening to the audio output from the speaker device. If correction
processing is performed on the band, it can be well adjusted while listening to music etc. to be
actually reproduced whether good reproduction output can be obtained. For example, when
raising the level of the small signal with respect to a certain frequency band, if the noise of the
reproduced sound becomes noticeable, the level of the small signal of the frequency band
avoiding that band may be raised.
[0035]
Also, for example, by applying the audio reproduction system of this example to a reproduction
system for a so-called car stereo mounted on a vehicle such as an automobile, generally small
noise is easily removed by noise in a reproduction environment where the influence of external
noise is large. The sound of the level can be easily heard, and the reproduction sound quality is
improved by performing processing particularly on the frequency band where the influence of
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the external noise is large.
[0036]
In the embodiment described above, although a specific example has not been particularly shown
for the division example of the frequency band to be subjected to the correction processing,
various division examples known as graphic equalizers can be applied.
For example, the audible band may be divided into a relatively small number of four bands, or
may be divided into ten or more bands.
[0037]
Further, instead of fixedly determining the division band by the prepared filter, the frequency
position and the frequency band width of each band can be variably set, and it may be possible to
set an arbitrary frequency band or the like to be subjected to correction processing. .
[0038]
In the above-described embodiment, a graphic equalizer is prepared as a dedicated audio signal
processing means (correction means) for performing correction processing, and it is configured
to be connected between an audio signal source and an amplifier device. A correction unit that
performs the same correction processing may be incorporated in various audio devices such as a
signal source, an amplifier device, or a speaker device to perform processing.
[0039]
Alternatively, an arithmetic processing device such as a personal computer device is provided
with a port capable of inputting / outputting an audio signal, and the arithmetic processing
device is implemented with a program for performing the same audio signal correction
processing. An apparatus for performing the correction process of
[0040]
Further, although the application to the system for 2-channel audio reproduction shown in FIG. 1
is assumed in the embodiment described above, it may be configured as a system for multichannel audio reproduction such as 5.1 channel.
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[0041]
It is a block diagram showing an example of system composition by one embodiment of the
present invention.
It is a block diagram which shows the structural example by one embodiment of this invention.
FIG. 6 is a characteristic diagram showing an example of correction characteristics according to
an embodiment of the present invention.
It is a characteristic view showing the output sensitivity for every frequency which showed the
example of the amendment state by one embodiment of the present 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. It is explanatory drawing which showed the example of the characteristic
of the conventional band EQ.
Explanation of sign
[0042]
DESCRIPTION OF SYMBOLS 10 Audio signal source 20 Amplifier device 30, 30 L, 30 R Speaker
device 31 Speaker unit 100 Graphic equalizer 101 Audio signal input terminal 102 Analog /
digital converter 103 Digital / analog Converter 104 audio signal output terminal 110 DSP
(digital signal processor) 111a to 111n band pass filter 112a to 112n variable dynamic range
controller 113 synthesis unit
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