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JP2007158589

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DESCRIPTION JP2007158589
PROBLEM TO BE SOLVED: To provide a sound field correction method, a sound field correction
device and an audio device capable of correcting the influence of a standing wave with high
accuracy. SOLUTION: The sound field correction device for correcting the influence of standing
waves in a sound field formed in a room, wherein the device determines the size of a rectangular
room based on a predetermined mathematical formula. A frequency calculating unit 32 that
calculates a group of theoretical resonance frequencies that characterizes a standing wave, a
frequency extracting unit 34 that extracts a predetermined number of peak frequencies from
frequency characteristics measured in a room, and the frequency extracting unit 34 The
frequency discrimination unit 36 discriminates the measured resonance frequency from the
theoretical resonance frequency calculated by the frequency calculation unit 32 for the
predetermined number of peak frequencies, and the frequency discrimination And a signal
processing unit that processes the signal to correct the influence of the standing wave based on
the measured resonance frequency determined by the unit. [Selected figure] Figure 1
Sound field correction method, sound field correction device and audio device
[0001]
The present invention relates to a sound field correction method in a room, a sound field
correction device, and an audio device.
[0002]
In a sound field formed in a room of a home or a car, a standing wave is generated by reflection
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from a wall or the like.
Standing waves in particular increase unnecessary frequency components on the low frequency
side and adversely affect the sound quality. Therefore, in order to achieve high fidelity sound
reproduction, it is desirable to be able to reduce the effects of standing waves.
[0003]
In order to adjust the influence of standing waves, a method has been proposed in which a peak
frequency with higher amplitude is detected from the result of measuring the indoor frequency
characteristics and the resonance frequency is determined as a standing wave (for example,
Patent Document 1) reference). In this method, at the time of sound field formation, based on the
determined resonant frequency, a sound having a phase opposite to that of the standing wave is
generated and output to cancel the standing wave in the room.
[0004]
Unexamined-Japanese-Patent No. 2000-115883
[0005]
However, in the above method, it is not consistent whether the detected peak frequency is a
resonant frequency (standing wave).
Therefore, the frequency which is not a standing wave may be determined as a standing wave,
and the fidelity of sound reproduction may be impaired. As described above, in the abovedescribed conventional method, it is difficult to accurately grasp the resonance frequency (the
standing wave) generated in the room with high accuracy, and the reproduced sound is corrected
with high accuracy to realize high fidelity sound reproduction. There was a problem that it was
difficult to do.
[0006]
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In view of the above circumstances, the present invention aims to provide a sound field
correction method, a sound field correction device, and an audio device capable of correcting the
influence of standing waves with high accuracy. Further, the present invention provides a sound
field correction method, a sound field correction device, and an audio device capable of
correcting the influence of the standing wave with high accuracy in order to accurately
determine and eliminate the resonance frequency characterizing the standing wave. The purpose
is to
[0007]
In order to achieve the above object, a sound field correction method according to a first aspect
of the present invention is a sound field correction method for correcting the influence of
standing waves in a sound field formed in a room, comprising: A frequency calculation step of
calculating a group of theoretical resonance frequencies characterizing standing waves from the
size of a room based on the following formula, and frequency extraction of extracting a
predetermined number of peak frequencies from frequency characteristics measured in the room
And a step of determining a predetermined resonance frequency from any of the theoretical
resonance frequencies calculated in the frequency calculation step for the predetermined number
of peak frequencies extracted in the frequency extraction step as a measured resonance
frequency. A signal processing system for processing a signal to correct an influence of a
standing wave based on a determination step, and an actual measurement resonance frequency
determined in the frequency determination step. Tsu includes a flop, the. (However, C: sound
velocity [m / s], L: room length [m], W: room width [m], H: room height [m], x, y, z: 0 or positive
Integer)
[0008]
According to the sound field correction method of the above configuration, the resonance
frequency that characterizes the standing wave generated in the room can be determined with
high accuracy. Therefore, it is possible to correct the standing wave while minimizing the
influence on the original frequency characteristics.
[0009]
The method configured as described above includes, for example, a size determination step of
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acquiring the size of a room. Alternatively, an input step may be provided to receive an input of
the size of a room from the user.
[0010]
In order to achieve the above object, a sound field correction device according to a second aspect
of the present invention is a sound field correction device for correcting the influence of a
standing wave in a sound field formed in a room, which has a rectangular shape. A frequency
calculation unit that calculates a group of theoretical resonance frequencies that characterize
standing waves from the size of a room based on the following formula, and frequency extraction
that extracts a predetermined number of peak frequencies from frequency characteristics
measured in the room And a frequency at which a predetermined number of peak frequencies
extracted by the frequency extraction unit is determined to be a measured resonance frequency
from any of the theoretical resonance frequencies calculated by the frequency calculation unit.
And a signal processing unit that processes a signal so as to correct the influence of a standing
wave based on the measured resonance frequency determined by the frequency determination
unit. (However, C: sound velocity [m / s], L: room length [m], W: room width [m], H: room height
[m], x, y, z: 0 or positive Integer)
[0011]
According to the sound field correction device having the above-described configuration, it is
possible to determine with high accuracy the resonance frequency that characterizes the
standing wave generated in the room. Therefore, it is possible to correct the standing wave while
minimizing the influence on the original frequency characteristics.
[0012]
The apparatus of the said structure is provided with the magnitude | size discrimination |
determination part which acquires the magnitude | size of a room, for example. Alternatively, an
input unit that receives an input of the size of a room from the user may be provided.
[0013]
The sound field correction device having the above configuration can be suitably applied to an
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audio device such as an amplifier and a player.
[0014]
According to the present invention, a sound field correction method, a sound field correction
device and an audio device capable of correcting the influence of standing waves with high
accuracy are provided.
Further, according to the present invention, there is provided a sound field correction method, a
sound field correction device and an audio apparatus capable of correcting the influence of the
standing wave with high accuracy by discriminating the resonance frequency characterizing the
standing wave with high accuracy. Be done.
[0015]
Hereinafter, embodiments of the present invention will be described in detail with reference to
the drawings. The embodiment described below is an example, and the present invention is not
limited to this. In the embodiment shown below, the present invention is applied to an audio
apparatus for amplifying and outputting an audio signal from a signal source as an example.
[0016]
The configuration of an audio device 10 according to an embodiment of the present invention is
shown in FIG. The audio apparatus 10 shown in FIG. 1 includes an input unit 12, an ADC (Analog
to Digital Converter) 14, a signal processing unit 16, a DAC (Digital to Analog Converter) 18, an
amplification unit 20, and an output unit 22. An operation input unit 24, an MPU (Micro
Processing Unit) 26, and a microphone input unit 28 are provided.
[0017]
The input unit 12 is connected to the signal source 3 such as a radio receiver or an optical disk
player, and receives an input of an audio signal from the signal source 13.
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[0018]
The ADC 14 converts the input analog signal into a digital signal.
Of course, if the input signal is a digital signal, it may not be provided.
[0019]
The signal processing unit 16 includes a digital signal processor (DSP: Digital Signal Processor),
applies predetermined processing to a digital audio signal, and outputs the signal. The processing
performed by the signal processing unit 16 includes a correction process of a standing wave
described later.
[0020]
The DAC 18 converts the digital audio signal from the signal processing unit 16 into an analog
signal.
[0021]
The amplification unit 20 amplifies the analog audio signal from the DAC 18.
[0022]
The output unit 22 supplies the analog audio signal from the amplification unit 20 to the speaker
23 connected to the output unit 22.
The speaker 23 is disposed inside the rectangular room.
The sound emitted from the speaker 23 forms a sound field inside the room. The room may be
rectangular and not limited to a specialized audit room, but may be a general living room or a car
interior.
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[0023]
The operation input unit 24 receives an operation input from the user regarding the operation of
the audio device 10. The operation input unit 24 includes an operation panel, a remote
controller, and the like.
[0024]
The microphone input unit 28 is connected to a terminal of the microphone 29 disposed in the
room, and receives an indoor audio signal received by the microphone 29. The microphone 29 is
used for preprocessing (device setting) of the use of the audio device 10.
[0025]
The MPU 26 controls the operation of the audio device 10 and sets the signal processing unit 16.
The MPU 26 may control only the signal processing unit 16, and the control unit of the audio
apparatus 10 may be provided separately from the MPU 26. The MPU 26 includes a magnitude
determination unit 30, a frequency calculation unit 32, a frequency extraction unit 34, a
frequency determination unit 36, and a setting unit 38.
[0026]
The size determination unit 30 determines the size (length, width, height) of the room. The size of
the room is calculated based on data collected by the user by outputting a pulse wave from the
speaker 23 and collecting the sound by the microphone 29 arranged by the user at the wall. For
example, the user places the microphone 29 at a position substantially perpendicular to one wall
from the speaker 23 and collects the pulse wave output from the speaker 23 with the
microphone 29.
[0027]
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The magnitude determination unit 30 compares the data of the output pulse signal with the data
of the detection signal to calculate a pulse delay amount. The size determination unit 30
calculates the size (one of length, width, and height) of one side of the rectangular room based on
the obtained pulse delay amount. Here, it is assumed that the speaker 23 is disposed along the
wall of the room. By correcting the size of the casing of the speaker 23, more accurate
measurement can be performed.
[0028]
The user arranges the microphones 29 for each of three sides of the room for the length, width,
and height of the room, and operates the audio device 10 to output a pulse wave and collect
sound. For example, the user places the microphone 29 at a desired position and then sets the
measurement mode from the operation input unit 24. By setting the measurement mode, the
audio apparatus 10 outputs a pulse signal and collects sound. The measurements are made for
each of the room length, width and height. The size determination unit 30 determines each value
based on the measurement result and stores the value in the memory 31.
[0029]
The memory 31 is composed of an EEPROM (Electrically Erasable Programmable Read-Only
Memory) or the like, and retains data even after the power of the audio apparatus 10 is turned
off. The data on the size of the room stored in the memory 31 can be changed by
remeasurement.
[0030]
The frequency calculation unit 32 calculates, based on the size of the room stored in the memory
31, a group of theoretical resonance frequencies characterizing the standing wave generated in
the room. Specifically, the frequency calculation unit 32 calculates a group of resonance
frequencies from the size (length, width, size) of a room based on a three-dimensional wave
equation (the following formula) related to a plane wave. The calculated resonant frequency is a
theoretical value determined from the size of an ideal rectangular room.
[0031]
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(However, C: sound velocity [m / s], L: room length [m], W: room width [m], H: room height [m], x,
y, z: 0 or positive Integer)
[0032]
The frequency extraction unit 34 extracts a frequency having a predetermined peak value from
the frequency characteristic of the measurement signal received by the microphone 29 for the
sine sweep signal emitted from the speaker 23 for test.
For example, for the measurement signal obtained through the microphone 29 when the sine
sweep signal is emitted from the speaker 23, the frequency extraction unit 34 increases and
decreases the peak value and dip value of the frequency by a predetermined degree larger than
the average level of the frequency characteristic. And extract the upper frequency with the larger
increase / decrease range. The number of frequencies to be extracted is determined by default
according to the processing capabilities of the MPU 26 and the signal processing unit 16, for
example.
[0033]
The frequency discrimination unit 36 compares the frequency extracted by the frequency
extraction unit 34 with the group of theoretical resonance frequencies stored in the memory 31
and determines the measured frequency within a predetermined frequency range from the
theoretical resonance frequency to the resonance frequency. It is determined as
[0034]
The setting unit 38 sets processing parameters of the signal processing unit 16 so as to eliminate
the influence of the standing wave, based on the frequency determined as the resonant frequency
by the frequency determination unit 36.
For example, the setting unit 38 sets processing parameters of the signal processing unit 16 so
as to remove the peak of the resonance frequency determined for the digital filter of the signal
processing unit 16. By doing this, the audio signal corrected for the resonance frequency in the
signal processing unit 16 is emitted from the speaker 23, and the sound field in the room has
high fidelity with the influence of the standing wave being eliminated.
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[0035]
Next, the operation of the audio apparatus 10 according to the present embodiment configured
as described above will be described. Before the audio device 10 is used in a normal state,
preprocessing for initializing the signal processing unit 16 is performed.
[0036]
In the preprocessing, first, the user sets the measurement mode from the operation input unit 24,
and causes the audio apparatus 10 to measure the size (length, width, height) of the room. That
is, the user places the microphone 29 in one direction of the room. The audio device 10 outputs a
pulse wave from the speaker 23 and collects the sound by the microphone 29. The user repeats
the measurement in three directions. The size determination unit 30 determines the size (length,
width, height) of the room based on the measurement result, and stores the size in the memory
31.
[0037]
The frequency calculation unit 32 reads a parameter indicating the size of the room from the
memory 31 and calculates a group of frequencies based on the above equation. In order to
improve the accuracy, the size of the casing of the speaker 23 may be automatically corrected.
[0038]
In the above equation, (x, y, z) can take any of 0, 1, 2, 3,... But preferably a predetermined
number of modes are taken into consideration. For example, in particular, standing waves (axial
waves) between opposing walls tend to be emphasized, (x, y, z) = (1, 0, 0), (2, 0, 0) ..., ( The modes
such as 0, 1, 0), (0, 2, 0), ..., (0, 0, 1), (0, 0, 2), etc. should mainly be considered (0 is the direction
It means that there is no standing wave). In addition, particularly considering the low frequency
range where the standing wave has a large influence on the sense of hearing, sufficient accuracy
can be obtained to some extent.
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[0039]
For example, in the case of an ideal rectangular room having a length L = 4.6 m, a width W = 4.1
m, and a height H = 2.55 m, only the low frequency range (500 Hz or less) is considered. It is
practically sufficient from the frequency group shown in the table of FIG. 2 with (x, y, z) being 10
or less. Of course, it may be calculated and used for a combination of a wider frequency range
and a larger number of modes. The theoretical resonance frequency group calculated by the
frequency calculation unit 32 is stored in the memory 31 as a table as shown in FIG.
[0040]
As the next pre-processing, the user sets, for example, the test mode from the operation input
unit 24, causes the signal source 13 to output a sine sweep signal, and causes the audio device
10 to measure the sound output from the speaker 23 through the microphone 29. The user
preferably places the microphone 29 in the listening position of the room. The frequency
extraction unit 34 extracts a peak frequency that satisfies a predetermined condition based on
the frequency characteristic of the obtained measurement signal. For example, the peak value
and the dip value of the frequency which is increased or decreased by about ± 8 dB more than
the average level of the frequency characteristic are extracted. The number of frequencies to be
extracted can be determined according to the processing capabilities of the signal processing unit
16 and the MPU 26, and is, for example, 10.
[0041]
The frequency discrimination unit 36 compares each frequency extracted by the frequency
extraction unit 34 with the theoretical resonance frequency group stored in the memory 31. The
frequency discrimination unit 36 discriminates, as a resonance frequency, a measured frequency
within a predetermined frequency range from the theoretical resonance frequency, for example,
within 3% (a value obtained by multiplying each theoretical frequency by 3%).
[0042]
The frequency distribution of the standing wave differs from the theoretical distribution
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determined from the size of the room depending on the wavelength, the state of the room, and
the listening position. Therefore, it is necessary to give the theoretical value a predetermined
width.
[0043]
The setting unit 38 sets processing parameters of the signal processing unit 16 so as to eliminate
the influence of the standing wave, based on the frequency determined as the resonant frequency
by the frequency determination unit 36. For example, the setting unit 38 sets parameters of the
digital filter of the signal processing unit 16 so as to remove the peak of the determined
resonance frequency. The parameters are held in the signal processing unit 16 or a storage unit
(not shown) provided elsewhere.
[0044]
The preprocessing is thus completed, and the signal processing unit 16 corrects, for the input
signal, a standing wave characterized by the resonance frequency with high accuracy. The signal
processing unit 16 corrects, for example, by parametric equalization. That is, the resonance
frequency determined by the frequency determination unit 36 is F0, and frequencies of levels
lower by a predetermined level (for example, 3 dB) from the peak or dip level of F0 are FL and
FH, and F0 / (FH−FL) is calculated Obtain a corrected Q value. In the inverse characteristic of
the obtained Q value, the deviation from the average value at F0 is used as a correction amount,
and is added to the frequency characteristic before correction. By performing correction for all
the obtained resonance frequency groups, high-fidelity frequency characteristics are obtained in
which only peaks due to standing waves are corrected.
[0045]
As described above, according to the present embodiment, it is possible to determine with high
accuracy the resonance frequency that characterizes the standing wave generated in the
rectangular room. As a result, it is possible to correct the standing wave inherent in the room
without correcting the original frequency characteristics, and it becomes possible to construct a
high fidelity sound field.
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[0046]
(Example) When an audio was output into an audio room with a length L = 4.6 m, a width W =
4.1 m, and a height H = 2.55 m, the frequency characteristics measured at a certain listening
position are shown in FIG. It was like that. In the frequency characteristics shown in FIG. 3, the
top 10 frequencies with large increase / decrease levels were 54 Hz, 62.0 Hz, 67.7 Hz, 83.9 Hz,
93.3 Hz, 173 Hz, 220 Hz, 310 Hz, 363 Hz, 404 Hz. . The size of the audio room was measured
using a pulse wave.
[0047]
By substituting the length L = 4.6 m, the width W = 4.1 m, and the height H = 2.55 m into the
above equation, a table of combinations of mode numbers as shown in FIG. 2 is obtained. The
table shown in FIG. 2 is obtained with (x, y, z) being 10 or less, considering only the low
frequency region (500 Hz or less).
[0048]
Such theoretical resonance frequency is compared with the peak frequency obtained by
measurement, and it is determined that the peak frequency corresponding to 3% of the peak
frequency corresponds. According to this, for the peak frequencies of 54 Hz, 67.7 Hz, 83.9 Hz,
220 Hz, 363 Hz and 404 Hz, corresponding theoretical frequencies exist, and the resonant
frequencies at which these frequencies characterize the standing waves It can be determined that
[0049]
On the other hand, there is no theoretical frequency corresponding to the measured 62.0 Hz,
93.3 Hz, 173 Hz and 310 Hz, and it can be judged that these peak frequencies are not due to
standing waves. Therefore, it is understood that it is possible to sort out the peak frequency
characterizing the standing wave from the peak frequencies.
[0050]
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In the above embodiment, the audio device 10 that amplifies and outputs the audio signal from
the signal source 13 has been described as an example. However, the present invention is not
limited to this, and the present invention is applicable to any audio device such as a playback
device, server, etc. that outputs an audio signal to form a sound field in a room.
[0051]
In the above embodiment, the size (length, width, height) of the room is measured using the
microphone 29 or the like. However, not limited to this, the size of the room may be directly
input by the user. In this case, in the configuration as shown in FIG. 4, the user inputs the size of
the room grasped in advance from the operation input unit 24, and the input value is stored in
the memory 31. Furthermore, assuming a standard house, a plurality of sets of room sizes
(length, width, height) are stored in memory 31 in advance, and the configuration can be selected
appropriately by the user according to the use environment. It is also good.
[0052]
It is a block diagram showing composition of an audio device concerning an embodiment of the
invention. It is a figure which shows an example of the group of theoretical resonance frequency.
It is a figure which shows the measured frequency characteristic. It is a block diagram which
shows the structure of the audio apparatus concerning other embodiment of this invention.
Explanation of sign
[0053]
10: audio apparatus, 12: input unit, 14: ADC, 16: signal processing unit, 18: DAC, 20:
amplification unit, 22: output unit, 23: speaker, 24: operation input unit, 26: MPU, 28:
Microphone input unit, 29: microphone, 30: size determination unit, 31: memory, 32: frequency
calculation unit, 34: frequency extraction unit, 36: frequency determination unit, 38: setting unit
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