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DESCRIPTION JP2004032339

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DESCRIPTION JP2004032339
A noise suppression method and apparatus for achieving a clear two-way simultaneous call even
under a noise environment of 100 dB (A) or more which has been made impossible by exhibiting
an effective noise removal effect, and a simultaneous noise reduction method It is an object of
the present invention to provide a two-way communication device. A simultaneous two-way
communication device according to the present invention is an absolute value for obtaining an
absolute value of signal amplitude in a DSP processing unit of an audio signal from the bone
conduction microphone using a bone conduction speaker and a bone conduction microphone.
Arithmetic unit 2, a level determiner 3 which determines whether or not the absolute value of the
signal amplitude exceeds a threshold to switch the output, a divider 5 which normalizes the
absolute value of the signal amplitude, and the divider It is characterized in that it incorporates a
noise suppressor comprising a square root calculator 6 for performing a square root operation
on the normalized signal normalized at 5. [Selected figure] Figure 3
Method and apparatus for noise suppression and simultaneous two-way communication
apparatus incorporating the method and apparatus
The present invention relates to a noise suppressing method and apparatus, and a simultaneous
two-way communication apparatus incorporating the method and apparatus, and more
particularly, to exert an effective noise removing effect, such as a construction site, etc. Method
and device for noise suppression that can realize a simultaneous two-way communication device
using a bone-conduction microphone and a bone-conduction speaker suitable for use under high
noise of the same, and a simultaneous two-way communication device incorporating the method
and device It is about [0002] Conventionally, a throat microphone (a laryngeal contact
microphone using tracheal anterior wall sound) is mainly used as a speech apparatus used under
high noise such as construction site noise, traffic noise, and noise in a tunnel. Alternatively, a set
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of close-talking microphones and speakers built into the earmuffs was used. However, in the case
of the above-mentioned call set, in the throat microphone, the feeling of wearing is bad because it
has to be worn on the neck, and in the close talk microphone, it has to be placed close to the
mouth. Was a problem that often In addition, the earmuffs have a bad feeling of wearing because
they have to be held down with a large side pressure, and they can not wear a helmet during use.
Furthermore, in the case of a throat microphone or a close talk microphone, there is a problem in
call sound quality as it is inevitable to pick up noise under high noise. As described above, the
combination of the earmuff built-in speaker and the throat microphone or the close-talking
microphone not only has problems with the call sound quality but also takes time and effort to
fit, and the wearing feeling is poor. The work was practically difficult. SUMMARY OF THE
INVENTION As described above, the present invention has been made in view of the fact that the
conventional telephone equipment used under high noise has many problems, and is effective.
Noise reduction method and apparatus for achieving clear two-way simultaneous call even under
a noise environment of 100 dB (A) or more, which has been made impossible, exhibiting various
noise removal effects, and a simultaneous two-way communication apparatus The challenge is to
provide The noise suppression method according to the present invention for solving the abovementioned problems is characterized in that the absolute value of the amplitude normalized by
the threshold is exceeded at the threshold from the received signal. Smoothly connect to the part
smoothly or approximately smoothly, and below the threshold, pass the function smaller than the
original amplitude, multiply the obtained amplitude by the obtained value, and attenuate the
noise below the threshold It is characterized by
A noise suppressor according to the present invention for solving the above problems comprises:
an absolute value calculator for obtaining an absolute value of a signal amplitude; and
determining whether or not the absolute value of the signal amplitude exceeds a threshold. It
comprises the level judging device which performs output switching, the divider which
normalizes the absolute value of the signal amplitude, and the square root calculator which
carries out the square root operation of the normal signal normalized in the divider. The
simultaneous two-way communication device according to the present invention for solving the
above problems uses a bone conduction speaker and a bone conduction microphone, and a
threshold value is obtained from a signal received for DSP processing of an audio signal from the
bone conduction microphone. The absolute value of the amplitude normalized by is smoothly or
approximately smoothly connected with the amplitude part above it at the threshold value, and
below the threshold value, it passes through a function smaller than the original amplitude, and
the obtained value is The present invention is characterized in that a noise suppression method is
adopted in which the amplitude is multiplied to attenuate noise below the threshold. In order to
solve the above problems, the simultaneous two-way communication device according to the
present invention uses a bone conduction speaker and a bone conduction microphone, and uses
DSP processing units for audio signals from the bone conduction microphone. An absolute value
calculator for obtaining an absolute value, a level determiner that determines whether or not the
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absolute value of the signal amplitude exceeds a threshold to switch the output, and a divider
that normalizes the absolute value of the signal amplitude And a square root calculator that
square-roots the normalized normal signal in the divider. The simultaneous two-way
communication device according to the present invention can be used by attaching it to a helmet
or other cap body, in which case the wearing of the helmet means the mounting of the instant
communication device. Embodiments of the present invention will be described with reference to
the attached drawings. In the simultaneous two-way communication device according to the
present invention, a bone conduction microphone is used as the microphone, and a bone
conduction speaker is used as the speaker. The bone conduction microphone is an acceleration
detection type, so it is difficult to pick up sound (air vibration) and is excellent in noise resistance.
In addition, since the bone conduction speaker can directly transmit the sound to the auditory
organ, it is possible to hear the sound sufficiently even under high noise only by inserting a
simple earplug into the ear canal. Basically, the bone conduction speaker and the bone
conduction microphone may be mounted anywhere on the head as long as they are in close
contact with the head, and the degree of freedom of attachment to a helmet or the like is large.
FIG. 1 shows an example of the appearance when the simultaneous two-way communication
device according to the present invention is attached to a helmet 11. The bone conduction
speaker 1 has left and right sides of the helmet 11, specifically a lower edge in the helmet 11. It
is fixed to a frame 12 extending along the part for attaching a chin strap or the like, and when
worn on the helmet 11, it comes into contact with the aurulus proximity part. Although not
shown, the bone conduction microphone is attached to, for example, the top of the frame 12 so
as to be in contact with the head when the helmet is worn. By installing the bone conduction
speaker 1 and the bone conduction microphone on the helmet 11 in this manner, the helmet 1
can be worn, that is, the bone conduction microphone and the bone conduction speaker 1 can be
attached to the head, For communication, it is not necessary to attach a speaker or a microphone
each time. In this device, both the microphone and the speaker use a bone conduction type, so if
simultaneous two-way communication is attempted, howling occurs. In order to solve this
problem, a howling canceller is incorporated in the DSP processing unit. In addition, there are
many cases where side tones are present in communications such as mobile phones and PHS,
and this also causes howling, so by incorporating a side tone canceller with the same function as
the howling canceler in the DSP processing unit, Try to avoid howling problems with tones. The
side tone canceller and the howling canceller can basically use existing ones as they are.
Although the bone conduction microphone is excellent in noise resistance, it picks up some noise
under high noise and degrades the speech quality. Therefore, in the present invention, the speech
quality is improved by incorporating a DSP-processed spectrum subtraction type noise canceller
at a stage subsequent to the howling canceller in the DSP processing unit. In general, a spectral
subtraction system emphasizes a target signal, has a large amount of noise suppression, and is
known as an effective noise canceller. Although this method calculates the spectrum of the
emphasis signal by obtaining the noise spectrum and subtracting it from the spectrum of the
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observation signal, in general, the noise spectrum has a dispersion, which causes a margin of the
noise spectrum. There is a fear that, due to the influence, noise called musical noise remains, and
there is a drawback that it is annoying.
In order to ameliorate this drawback, the inventor has devised a noise suppression method as
described later. For noise suppression of small amplitude, a noise gate is often used to shut off
the signal transmission circuit when there is no signal. Fig. 2 is a block circuit diagram showing
the configuration of the noise gate. The level determiner determines whether or not the absolute
value of the signal amplitude exceeds the threshold, and the original signal is output when the
absolute value of the signal amplitude exceeds the threshold. When the absolute value of the
signal amplitude is equal to or less than the threshold value, “0” is output to switch the output
switch. [0022] With this noise gate, all small amplitude signals are cut off, so the necessary
signal of small amplitude is not passed at all, and there is a drawback that the call is unnatural.
The present invention proposes a novel noise suppressor that improves the conventional noise
gate in order to improve this unnaturalness. FIG. 3 is a block circuit diagram showing the
configuration of the noise suppression apparatus according to the present invention, in which the
level judging unit 3 judges whether the absolute value of the signal amplitude exceeds a
threshold value, Switch. The divider 5 divides the absolute value of the signal amplitude by a
threshold and normalizes it. The normalized signal is subjected to a square root operation by the
square root operator 6, and multiplied by the original signal by the multiplier 7. When the
absolute value of the signal amplitude is less than the threshold value, the output of the
multiplier 7 is output. The procedure for processing the received signal in this noise suppressor
is as follows. (1) The absolute value calculator 2 calculates the absolute value of the original
signal. (2) The level determiner 3 determines whether the absolute value is equal to or less than a
threshold. (3) If the absolute value exceeds the threshold value, the original signal is output as it
is. (4) If the absolute value is less than or equal to the threshold value, the following process is
performed. (5) The above-mentioned absolute value is divided by the threshold by the divider 5
to perform normalization with the threshold being 1. (6) The square root computing unit 6 finds
the square root of the division result, that is, the multiplication coefficient for noise suppression.
(7) The square root and the original signal are multiplied by the multiplier 7 to obtain an output.
In the noise suppression method according to the present invention, the absolute value of the
amplitude normalized by the threshold is smoothly or approximately smoothly connected with
the amplitude portion exceeding the threshold at the threshold, and below the threshold The
original amplitude is multiplied by a function smaller than the original amplitude, and the
original amplitude is multiplied by the obtained value so that noise below the threshold value is
attenuated. Here, “amplitude part and smooth” means that the slope (differential value) in the
vicinity of the threshold changes continuously, and that a discontinuous point does not exist in
the waveform.
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Further, “approximately smooth” means that even if the slope (differential value) in the vicinity
of the threshold is discontinuous, jumping of the differential value at the discontinuous point is
small. Examples of the function used for the above noise suppression method include the
following. F (x) = (| x |) ^ (1/2) In addition, although the following function is used to obtain
smoothness, it is possible to use well-known mathematical methods other than this function. it
can. F (x) = (1- (x-1) ^ 2) ^ (1/2) Note that, based on the above processing procedure, for a signal
including noise whose absolute value is less than or equal to the threshold value, The signal is
multiplied by the square root of the absolute value and the signal amplitude is closer to the
threshold, the amount of suppression is reduced and the signal is smoothly connected with the
threshold or more, and the amount of suppression is increased as the signal amplitude is
decreased. An example program for improving the aural SN ratio is as follows. <Img class =
"EMIRef" id = "197693352-000003" /> FIGS. 4 to 6 show output waveforms in a comparison test
performed to confirm the effectiveness of the present invention. is there. When the noise
canceller and the noise suppressor are both turned off (FIG. 4), only the noise canceler is turned
on (FIG. 5), and the noise canceller and the noise suppressor are input. FIG. 6 shows output
waveforms when both are on (FIG. 6). According to this, in the case of FIG. 5, although the noise
level is lowered by about 10 dB, in the case of FIG. 6 while the unpleasant noise (musical noise)
of Hulhull remains. It can be seen that musical noise is suppressed and low-level natural noise is
obtained, and the effectiveness of the present invention can be confirmed. The present invention
is as described above, and according to the noise suppression method and the noise suppression
device according to the present invention, signals below the threshold are suppressed but not
blocked. Since the continuity is maintained, highly natural noise suppression is possible. In
addition, since the operation requires only a simple square root, there is an effect that can be
realized by a small circuit or a simple program. Also, in the simultaneous two-way
communication device incorporating the noise suppression device according to the present
invention, clear two-way simultaneous communication is possible even under a high noise
condition of 100 dB (A) or more, which was impossible conventionally. Therefore, when
attaching it to a helmet or other cap body, it becomes very easy to install, and comfortable fit is
obtained, and when it is used at a construction site etc. efficiency improvement and safety etc. of
construction etc. There is also an effect that can contribute.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing a simultaneous two-way
communication device according to the present invention attached to a helmet. FIG. 2 is a block
diagram of a noise gate in a general configuration. FIG. 3 is a block diagram of a noise
suppression apparatus according to the present invention. FIG. 4 is an output waveform diagram
in a test for confirming the effectiveness of the noise suppression device according to the present
invention. FIG. 5 is an output waveform diagram in the effectiveness confirmation test of the
noise suppression device according to the present invention. FIG. 6 is an output waveform
diagram in the effectiveness confirmation test of the noise suppression device according to the
present invention. [Description of the code] 1 bone conduction speaker 2 absolute value
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calculator 3 level judging device 4 output switching device 5 divider 6 square root calculator 7
multiplier 11 helmet 12 frame
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