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JPH0590856

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DESCRIPTION JPH0590856
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
parametric equalizer for correcting acoustic frequency characteristics. In particular, the present
invention aims to improve correction accuracy by simple processing in the parametric equalizer.
[0002]
2. Description of the Related Art In recent years, audio devices are used in various places. An
audio frequency characteristic correction device is provided which automatically performs
correction to flatten the frequency characteristic by the parametric equalizer because the sound
frequency characteristic has peaks and dips depending on the space where the sound reproduced
by the audio device is used It has increased. The automatic acoustic frequency characteristic
correction apparatus will be described in detail in the embodiment section. The effect is
remarkable especially when used in a place where space is narrow and susceptible to sound
distortion as in a car.
[0003]
However, the conventional automatic sound frequency characteristic correction apparatus has
the following problems when correcting the frequency. FIG. 6 is a diagram for explaining
correction in a conventional automatic sound frequency characteristic correction apparatus. The
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horizontal axis of this figure represents frequency, and the vertical axis represents sound level.
This figure (a) represents the acoustic characteristic of space, and the peak has arisen in the
frequency of about 200 Hz. The automatic acoustic frequency characteristic correction device
automatically detects and corrects this peak and dip. This figure (b) shows the correction |
amendment equalizer curve by a parametric equalizer, and it cancels and correct | amends
distortion by moderate sharpness (Q) by center frequency about 200 Hz. By the way, space
distortion is often asymmetrical with respect to the center frequency. For this reason, in the case
of the correction shown in FIG. 7 (b) where the peak frequency is simply set as the center
frequency of the equalizer as it is, a portion not corrected is generated as shown in FIG.
[0004]
Therefore, in view of the above-mentioned problems, the present invention aims to improve
correction accuracy by making it possible to easily correct acoustic distortion in space.
[0005]
SUMMARY OF THE INVENTION The present invention is an automatic acoustic frequency
characteristic correction apparatus for correcting peaks and dips of acoustic frequency
characteristics produced in a space-propagating sound, in order to solve the above-mentioned
problems. A correction is made to shift the center frequency of the peak or dip according to the
asymmetry of the shape of the peak or dip.
Alternatively, the sharpness is determined and corrected according to the asymmetry of the
shape of the peak or dip in frequency distortion. According to the asymmetry of the shape of the
peak or dip in the acoustic frequency characteristic, the center frequency of the peak or dip may
be shifted and the sharpness may be determined to be superimposed and corrected. Specifically,
the correction is a matrix of central frequencies and sharpnesss to be offset with the amount of
attenuation in the adjacent bands on the left and right with respect to the central frequency of
the peak or dip in the frequency distortion obtained by dividing into multiple bands. It may be
previously stored and set in the parametric equalizer.
[0006]
According to the automatic sound frequency characteristic correction apparatus of the present
invention, the center frequency of the peak or dip is shifted and the sharpness is determined and
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corrected according to the asymmetry of the shape of the peak or dip in the sound frequency
characteristic. Therefore, it is possible to easily improve the accuracy of correcting frequency
distortion that occurs in the sound propagating in space. Furthermore, the central frequency and
the sharpness to be shifted are parameterized beforehand and stored in the form of a matrix
using the attenuations of the adjacent bands on the left and right with respect to the central
frequency of the peak or dip, and these are set in the parametric equalizer. The microcomputer
processing is simplified, and the frequency to be set from the above matrix to the parametric
equalizer can be easily calculated by interpolation or the like.
[0007]
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a view showing an automatic sound frequency characteristic correction apparatus as a
premise of the present invention. First, the entire configuration will be described. The automatic
sound frequency characteristic correction device shown in the figure generates a reference signal
having a flat frequency characteristic in the audible range for measuring the space characteristic
and the sound reproduction device 1 using CD cassettes, tape decks, FM broadcasts, etc. as sound
sources. Pink noise generator 2, a switch 3 for alternatively selecting the sound reproducer 1 and
the pink noise generator 2, a parametric equalizer 4 for correcting acoustic distortion in space,
and power amplification of the signal after correction Power amplifier 5, a speaker 6 for
converting a power-amplified electric signal into sound, a microphone 7 installed near the
listening point from the speaker 6 via a space, and converting the propagated sound into an
electric signal; A power amplifier 8 for power amplifying a signal of the microphone 7 and a van
for dividing the signal from the power amplifier 8 into a plurality of frequency bands, for
example, one octave. A pass filter 9, a detection unit 10 that detects and averages output signals
of each frequency band of the band pass filter 9, a selector unit 11 that processes signals from
the detection unit 10 in a time division manner, and the selector unit 11 comprises an A / D
converter 12 (Analog to Digital Converter) for converting an analog signal from 11 into a digital
signal, and a microcomputer, and outputs the signal to the parametric equalizer 4 based on the
signal from the A / D converter 12 And a control unit 13 that forms a correction signal to be
generated.
[0008]
Next, the operation of this embodiment will be described. FIG. 2 is a diagram for explaining a
series of operations of the present embodiment. When detecting an acoustic frequency
characteristic, the switch 3 switches the acoustic reproduction device 1 to the pink noise
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generator 2 and outputs pink noise having a flat frequency characteristic in the audible range as
a reference output to the parametric equalizer 4 (step 1) ). The reference output is converted to
an acoustic signal by the speaker 6 through the parametric equalizer 4 and the power amplifier 5
which are initially set to a flat (flat) which is not corrected at all. Propagated to As described
above, when pink noise is reproduced by the speaker 6, pink noise is collected by the
microphone 7, and the band pass divided by the band pass filter 9 through the power amplifier 8
in each band, for example, one octave. After passing through the filter 9, detection and
rectification is performed by the detection unit 10, and the A / D converter 12 converts it into
digital data and outputs it to the control unit 13 (step 2). In order to adjust the parametric
equalizer 4, the control unit 13 determines the peak or dip point from the level of each of the
band pass filters 9 (step 3) FIG. 3 is a diagram for explaining the acoustic frequency
characteristics and the peak and dip correction method. It is. In the control unit 13, when a signal
is input from the A / D converter 12, the frequency is taken along the vertical axis as shown in
FIG. Space distortion is determined. Here, an example in which one peak and one dip are detected
is shown. The shape of the peak and dip is influenced by the size and shape of the space, for
example, while the attenuation of the sound pressure in the band adjacent to the left is a for the
sound pressure of the peak frequency f0 at peak time. In the adjacent portion, the attenuation
amount of the sound pressure in the band is b, and the a and b may be different and the
attenuation amount may be asymmetrical. In order to cope with such a case, the control unit 13
has a matrix as shown in FIG. In the matrix of this figure (b), the attenuation a of the left band of
the peak is taken as a parameter in the horizontal direction, and the attenuation b of the right
band is taken as a parameter in the vertical direction. I do. In the figure (b), +1 of the bias means,
for example, setting the center frequency to 1/3 octave right with respect to the center
frequency f0, and +2 means setting the center frequency to 2/3 octave right. Do. -1 means to set
the center frequency to 1/3 octave left with respect to the center frequency f0, and -2 means to
set the center frequency to 2/3 octave left.
0 indicates no bias.
[0009]
FIG. 4 is a diagram for explaining the correction by the automatic sound frequency characteristic
correction device of this embodiment. In this figure (a), as an example, if the level of a is -7 dB
and the level of b is -1 dB, +2 is determined from the above matrix and the center frequency of
the parametric equalizer 4 is shifted to the right by 2 octaves from the peak frequency. It is
controlled to match. At this time, the center frequency of the parametric equalizer 4 is shifted to
the right from 200 Hz to 315 Hz as shown in FIG. This figure (c), which is easily obtained by
interpolation or extrapolation when not shown in the matrix, shows the correction result, and
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there is no part that is not corrected as in the prior art (step 4).
[0010]
FIG. 5 is a view for explaining a method of correcting the space distortion and the sharpness (Q).
Sharpness (Q) is previously obtained for the parameters a and b from the shapes of peaks and
dips shown in FIG. The control unit 13 obtains the sharpness together with the center frequency
from the matrix based on the parameters a and b from the peak and the dip (step 5). The center
frequency and the degree of sharpness thus obtained are set in the parametric equalizer 4 (step
6). The above procedure is repeated until the target characteristic is obtained (step 7).
[0011]
As described above, according to the present invention, correction is performed to shift the
center frequency of the peak or dip according to the asymmetry of the shape of the peak or dip
in the acoustic frequency characteristic. The accuracy of correcting the characteristics can be
easily improved.
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