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DESCRIPTION JP2007150737

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DESCRIPTION JP2007150737
An object of the present invention is to reduce long continuous noise. SOLUTION: An input
means 1 for inputting an audio signal, a timing generation means 10 for generating a gap period
according to an occurrence period of noise mixed in from a noise generation source contained in
an audio signal, and a noise removing means for removing noise 3 according to the signal level
from the level envelope detecting means 25 for detecting the level envelope of the audio signal
continuously and the signal level from the level envelope detecting means 25 and a coefficient
for generating a coefficient according to the level envelope within the gap period Level
modulation means 24 for level modulating the signal from the generation means 26,
interpolation signal generation means 22 and interpolation signal generation means 22 with the
coefficient from the coefficient generation means 26, Output from the noise removal means 3
and level modulation means The signal from the combining means 21 is outputted from the
combining means 21 for combining the output from the signal generator 24 and the period
corresponding to the gap period. And, other than the gap period and a switching means 4
outputs the audio signal. [Selected figure] Figure 1
Audio signal noise reduction device and method
[0001]
The present invention relates to, for example, an audio signal noise reduction apparatus and
method for reducing noise of an audio signal which is built in a digital home appliance and
recorded from a small microphone.
[0002]
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1
In recent years, digital home appliances that incorporate a compact microphone in the body such
as a video camera, digital camera, IC recorder, etc. have been miniaturized more and more easily,
and can easily touch the vicinity of the microphone during recording or click on various function
switches SW. The noise transmitted to the cabinet is mixed into the microphone, and in many
cases, shock noise, touch noise and click noise which are difficult to hear during reproduction
may be generated.
In addition, recording devices such as tape devices and disk devices built into digital home
appliances and built-in microphones are close to each other, and vibration noise and acoustic
noise generated from the recording devices may be inputted to the microphone. There is.
[0003]
For this reason, in order to reduce these noises conventionally, the microphone unit of the builtin microphone is floated from the cabinet by an insulator such as a rubber damper, or the
microphone unit is hollowed by a rubber wire or the like. The vibration transmitted from the
cabinet was absorbed so that these noises were not transmitted to the microphone unit. However,
even with this method, all vibrations can not be suppressed, and depending on the strong
vibration or vibration frequency, the effect of the insulator may not be achieved, or the resonance
vibration may occur at a specific frequency. It has been an obstacle to miniaturization.
[0004]
On the other hand, although various noise removal methods have been proposed, the noise
mentioned above is not only due to the vibration transmitted through the cabinet, but also
generates acoustic noise which propagates as sound in the air together with the vibration. As a
result, the noise transmission path to the microphone unit is complicated, and the conventional
passive method has a limit in the reduction of the noise, and the level has not reached a level that
the photographer or the like can satisfy.
[0005]
Therefore, the present applicant has proposed a noise reduction method for the same purpose in
Patent Document 1 (microphone device, noise reduction method and recording device).
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In Patent Document 1, a pseudo noise signal is generated using an adaptive filter, and noise
reduction is realized by subtracting the pseudo noise signal from an audio signal including noise.
JP 2005-57437 A
[0006]
However, in this patent document 1, the adaptive filter used for the noise reduction tends to
require more taps as the noise signal to be approximated becomes wider and as the time of one
continuous interval becomes longer. There is. For example, at a sampling frequency of 48 kHz, an
adaptive filter of about 480 taps is required to approximate the noise waveform in the 10 mS
section up to the Nyquist frequency. Therefore, since this operation process requires productsum operations several times the number of taps per sample, the operation scale increases, and
hardware such as a large logic circuit or high-speed DSP (Digital Signal Processor) is required.
there were. Moreover, since the time delay by arithmetic processing can not be disregarded, and
it becomes necessary to delay an audio signal simultaneously, there existed a case where sound
collection was impossible in real time.
[0007]
By the way, as a feature of shock noise, touch noise, and click noise as described above, it does
not always occur continuously in time, and generation is limited only at the time of shock, so a
time of about several ms to several tens of ms In most cases, it occurs suddenly. Therefore, the
present applicant has proposed in Japanese Patent Application No. 2004-117248 (a noise
reduction method and apparatus) (hereinafter referred to as the above-mentioned prior
application), an effective noise reduction method by utilizing a masking phenomenon by human
hearing. did.
[0008]
Here, the human auditory masking phenomenon is described. The human hearing does not notice
the presence of a small sound that is behind a relatively loud sound so that the human voice is
difficult to hear in loud noise. Such a phenomenon is called masking phenomenon and has been
studied for a long time, and is known to depend on characteristics such as frequency
components, sound pressure level, and duration, but the detailed mechanism is still studied It is
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on the way.
[0009]
This auditory masking phenomenon is roughly divided into frequency masking and temporal
masking, and temporal masking is further divided into simultaneous masking and nonsimultaneous masking (also called successive masking). At present, this masking phenomenon
has also been applied to high efficiency coding for compressing an audio signal of a CD (compact
disc), for example, to 1/5 to 1/10.
[0010]
The non-simultaneous masking phenomenon mainly used in the prior application will be
described with reference to FIG. In FIG. 11A, the vertical axis represents the absolute value of the
signal level, and the horizontal axis represents the passage of time. First, the signal A is input at a
predetermined level, and the signal B is input at a predetermined level after a no signal gap
period. The case is shown. At this time, the human hearing level is schematically shown as shown
in FIG. 11B. That is, in the human sense of hearing, the pattern of the signal A remains for a while
after the signal A leaves, although the sensitivity decreases for a while. This is called forward
(forward) masking and can not be heard even if another sound is present in the shaded area of
the figure. Next, the sensitivity reduction which can not be heard immediately before the input of
the signal B occurs, which is called backward (reverse direction) masking, and can not be heard
even if another sound is present in the hatched portion of the figure.
[0011]
Usually, the amount of forward masking is larger than the amount of backward masking, and
although depending on the conditions in time, up to several hundreds of ms occur. Under certain
conditions, the gap period in FIG. 11 is not perceived audibly, and a phenomenon occurs in which
the signal A and the signal B can be heard as continuous sound. Plomp's research paper on gap
detection (1963), Miura (Sony, JAS. Journal 94. November), and an overview of auditory
psychology (B. C. J. As shown in Moore, Kengo Ohori, Seishin Shobo, Chapter 4 / Time resolution
of the auditory system), under the following conditions, the time gap will not be recognized up to
several mS to several tens of mS or more.
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[0012]
(1) If there is a correlation between the frequency bands of the signal A and the signal B, the gap
length increases, or if the continuity between the signal A and the signal B is maintained in
frequency, the gap length increases. (2) The gap length of the band signal is larger than that of a
single sine wave. (3) If the levels of the signal A and the signal B are the same, the smaller the
gap length, the smaller the gap length. If the level becomes larger than a certain level, the gap
length does not change. (4) When the level of the signal B is smaller than that of the signal A, the
gap length is larger. (5) The gap length is larger as the center frequency included in the signal is
lower, and the gap length is smaller as the frequency is higher.
[0013]
As described above, the shock noise and the touch noise described above are applied so that the
human auditory sense is not recognized based on the detection conditions of the gap length
(these conditions are referred to as masking conditions (1) to (5) in the following description).
Although click noise is removed, the prior application, Japanese Patent Application No. 2004117248 (noise reduction method and apparatus) is to control the gap length appropriately in
accordance with the masking condition when the noise occurs. However, under conditions where
the gap length in the above masking condition is small, from the masking condition (2) in one
example, when the signals A and B are tone signals close to a sine wave, or from the masking
condition (3), If the levels of the signals A and B are relatively large, or if the frequency bands
included in the signals A and B are relatively high in frequency due to the masking condition (5),
noise generated more than the gap length to be masked The period may be longer, which causes
a problem that some periods of the noise signal can not be removed.
[0014]
An example of the noise reduction device of the above-mentioned prior application, Japanese
Patent Application No. 2004-117248 (noise reduction method and apparatus) will be described
with reference to FIG. In this example, it is an object to reduce noise generated by a seek
operation in a disk device such as an HDD (Hard Disk Drive). First, information is read and
written by a magnetic head 15 attached to a VCM (voice coil motor) 14 on a magnetic film on the
surface of the hard disk 16, but the hard disk 16 maintains a predetermined number of
revolutions by a spindle motor 17 It is controlled by the servo signal 11 from the DSP (digital
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signal processor) built-in microcomputer 10 as follows. The VCM 14 is similarly driven by the
position control signal 13 from the DSP built-in microcomputer 10 so that the magnetic head 15
is controlled to read / write data at a predetermined position of the hard disk 16.
[0015]
The noise generated during the seek operation is caused by the vibration of the actuator portion
generated when the VCM 14 accelerates and decelerates the magnetic head 15 rapidly to the
data read / write position on the disk. At the same time, the noise timing signal 12 is output from
the DSP built-in microcomputer 10 to the gap period generating means 8. The microphone 1 is
an arbitrary microphone unit, and the negative terminal of the output of the microphone 1 is
grounded to the ground (GND) of the circuit, the positive terminal is connected to the amplifier
(AMP) 2, and the output signal is taken out Be
[0016]
This output signal is supplied to one fixed contact 4a of the changeover switch 4 and is also
supplied to the other fixed contact 4b of the changeover switch 4 via the noise removal means 3,
and is further input to the level detection means 6 The level is detected, and the amount of
masking is determined by the amount of masking determining means 7 from the sound level, and
the amount of masking is output to the gap period generating means 8 described above. Then, in
accordance with the gap length generated here, the signal selected by the above-described
changeover switch 4 is output from the output terminal 5 via the movable contact 4c.
[0017]
Here, the operation of the noise reduction apparatus shown in FIG. 12 will be described. The
microphone 1 outputs a signal in which a noise signal from the HDD is mixed into the audio
signal, but as described above, the target noise is not continuously generated temporally and is
limited only to the impact. At the time of non-impact, the movable contact 4c of the changeover
switch 4 is controlled to be connected to one fixed contact 4a so that the audio signal from the
microphone 1 is output as it is. The movable contact 4c of the changeover switch 4 is switched to
the other fixed contact 4b side only during the gap period, and the noise removing means 3 cuts
off the noise signal.
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[0018]
At the same time, when an audio signal is also input, this audio signal is also blocked, but the
level of the input audio signal is detected by the level detection means 6, and from this level, the
masking amount determination means 7 and the gap period generation Means 8 generates a gap
period masked in the human auditory sense, and controls the time for connecting the movable
contact 4c of the changeover switch 4 to the other fixed contact 4b according to the gap time.
[0019]
Next, another example of the noise reduction device of the prior application will be described
with reference to FIG. 13, but the portions corresponding to FIG.
This example of FIG. 13 targets touch noise and click noise. First, the microphone 1 is an
arbitrary microphone unit, and the negative side terminal of the output of the microphone 1 is
grounded to the circuit ground (GND) and the positive side terminal is It is connected to an
amplifier (AMP) 2 and an output signal is taken out.
[0020]
The sensor 18 has its negative terminal grounded to the circuit ground (GND), its positive
terminal connected to the amplifier (AMP) 19, and its output signal inputted to the comparator
20. The signal level is compared with the signal level of the REF (reference) level set separately
from the input terminal 9, and the result is output from the comparator 20 to the gap period
generating means 8.
[0021]
The output signal of the amplifier 2 described above is supplied to one of the fixed contacts 4a of
the changeover switch 4 and is input to the level detecting means 6 to detect an audio level. The
amount of masking is determined and output to the gap period generating means 8 described
above.
Then, according to the gap length generated here, the signal selected by the above-mentioned
changeover switch 4 whose other fixed contact 4b of this changeover switch 4 is grounded to the
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circuit ground (GND) is outputted from the output terminal 5 Ru.
[0022]
Here, the operation of another example of the noise reduction device of the prior application of
FIG. 13 will be described. The microphone 1 outputs a signal in which a noise signal from a noise
source is mixed into an audio signal, but as described above, the target touch noise and click
noise are not continuously generated temporally but at the time of impact. Therefore, the
movable contact 4c of the changeover switch 4 is controlled to be connected to one fixed contact
4a so that the sound signal from the microphone 1 is output as it is during non-impact. Only
when an impact is detected, the movable contact 4c of the changeover switch 4 is switched to the
other fixed contact 4b (GND) side and connected to interrupt the noise signal.
[0023]
At the same time, when an audio signal is also input, this audio signal is also blocked, but the
level of the input audio signal is detected by the level detection means 6, and based on this level,
the masking amount determination means 7 and the gap period The generation means 8
generates a gap period to be masked by human hearing, and controls the time for switching and
connecting the movable contact 4c of the changeover switch 4 to the other fixed contact 4b
(GND) side according to the gap period I am trying to do it.
[0024]
Further, in the above-mentioned comparator 20, for example, when the vibration signal
outputted from the sensor 18 is larger than the level set by the reference level input 9, it is
judged as an impact, and conversely, when it is smaller, it is judged as no impact. .
Then, the masking amount determination means 7 makes the gap period longer when the level
from the level detection means 6 is smaller than the case where the audio level is large according
to the masking condition (3) described above. Further, from the masking condition (4), the gap
generation period is controlled by determining that the gap period can be made longer in the
case of the downward tendency than in the case of the audio level tending to rise temporally.
[0025]
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8
An object of the present invention is to improve the above prior application so that long-running
noise can be reduced.
[0026]
An audio signal noise reduction apparatus according to the present invention comprises: input
means for inputting one or more audio signals; timing generation means for generating a gap
period corresponding to a generation period of noise mixed from a noise generation source
contained in the audio signal; Noise removal means for removing noise from the audio signal,
level envelope detection means for continuously detecting the level envelope of the audio signal,
and within the gap period according to the signal level from the level envelope detection means
Means for generating a coefficient corresponding to the level envelope, an interpolation signal
generating means, level modulation means for level modulating a signal from the interpolation
signal generating means with a coefficient from the coefficient generation means, and Combining
means for combining the output from the noise removing means and the output from the level
modulating means, and corresponding to the gap period That period outputs a signal from the
combining means, other than the gap period is one and a switching means for outputting the
audio signal.
[0027]
An audio signal noise reduction apparatus according to the present invention comprises: input
means for inputting one or more audio signals; timing generation means for generating a gap
period corresponding to a generation period of noise mixed from a noise generation source
contained in the audio signal; Noise removal means for removing noise from the audio signal,
level envelope detection means for continuously detecting the level envelope of the audio signal,
and a signal level from the level envelope detection means for detecting Masking level
determination means for determining the level to be masked in the auditory sense; interpolation
signal generation means; level modulation means for level modulating the signal from the
interpolation signal generation means with a coefficient generated from the masking amount
determination means; Combining means for combining the output from the noise removal means
and the output from the level modulation means , A period corresponding to the gap period,
outputting a signal from the combining means, other than the gap period is one and a switching
means for outputting the audio signal.
[0028]
An audio signal noise reduction apparatus according to the present invention comprises: input
means for inputting one or more audio signals; timing generation means for generating a gap
period corresponding to a generation period of noise mixed from a noise generation source
contained in the audio signal; Noise removal means for removing noise from the audio signal,
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level envelope detection means for continuously detecting the level envelope of the audio signal,
and within the gap period according to the signal level from the level envelope detection means
Means for generating level coefficients according to the level envelope, spectrum envelope
detection means for continuously detecting the frequency spectrum of the audio signal, and
spectrum information from the spectrum envelope detection means To generate a spectral
coefficient within this gap period. Means, interpolation signal generation means, level modulation
means for level modulating the signal from the interpolation signal generation means with the
coefficient from the first coefficient generation means, and frequency according to the coefficient
from the second coefficient generation means The combining means for combining with the
output from the noise removing means through the variable filter means for modulating, the
signal from the combining means is output during a period corresponding to the gap period, and
the voice signal is output except for the gap period And switching means.
[0029]
The audio signal noise reduction method according to the present invention generates a gap
period according to the generation period of noise mixed from a noise source included in one or
more input audio signals, and continuously makes the level envelope of the audio signal
continuous. To generate a coefficient corresponding to the level envelope according to the
detected signal level, generate an interpolation signal, level modulate the interpolation signal
with the coefficient, and output the level modulation output and the voice signal. The noiseremoved output from which noise has been removed is combined, the combined signal is output
in a period corresponding to the gap period, and the voice signal is output as it is in other
periods than the gap period.
[0030]
The audio signal noise reduction method according to the present invention generates a gap
period according to the generation period of noise mixed from a noise source included in one or
more input audio signals, and continuously makes the level envelope of the audio signal
continuous. To determine the level to be masked by human hearing in this gap period from this
detection signal level, to generate an interpolation signal, and to level modulate this interpolation
signal with a coefficient generated by this masking level determination. The level modulation
output and the noise removal output obtained by removing noise from the voice signal are
combined, the combined signal is output in a period corresponding to the gap period, and the
voice signal is output as it is in other periods than the gap period. It is a thing.
[0031]
The audio signal noise reduction method according to the present invention generates a gap
period according to the generation period of noise mixed from a noise source included in one or
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more input audio signals, and continuously makes the level envelope of the audio signal
continuous. To generate a level coefficient according to the level envelope according to the
detected signal level, to continuously detect the frequency spectrum of the speech signal, and to
detect the spectrum within the gap period according to the detected spectrum information. A
coefficient is generated, an interpolation signal is generated, and the interpolation signal is levelmodulated by the level coefficient and frequency-modulated by the spectrum coefficient, and the
level modulation output and the noise removal output obtained by removing noise from the voice
signal The synthesized signal is output during a period corresponding to the gap period, and the
voice signal is output outside the gap period. It is intended to output as it is.
[0032]
According to the present invention, since level envelope interpolation is performed using a signal
that separately generates a gap period, noise that is continuous for a long time can also be
reduced.
[0033]
According to the present invention, in consideration of temporal masking of human auditory
masking, the lack of masking ineffectiveness during the gap period is interpolated, so that longlasting noise can be reduced. .
[0034]
Further, according to the present invention, not only the level modulation but also the frequency
characteristic of the signal to be interpolated within the gap period is made variable, so that the
continuity of the signal can be maintained and the masking effect can be further enhanced.
[0035]
Hereinafter, examples of the best mode for carrying out the audio signal noise reduction
apparatus and method of the present invention will be described with reference to the drawings.
In FIG. 1, parts corresponding to those in FIG. 12 are assigned the same reference numerals and
detailed explanations thereof will be omitted.
[0036]
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11
In the example of FIG. 1, the noise timing signal 12 generated from the DSP built-in
microcomputer 10 controlling the HDD as in FIG. 12 is directly used as a control signal of the
changeover switch 4 and at the seek operation, the movable contact 4c of the changeover switch
4 Is controlled to connect to the other fixed contact 4b to select the signal from the adder 21.
Otherwise, the movable contact 4c of the changeover switch 4 is controlled to be connected to
one fixed contact 4a. The audio signal of is selected from the output terminal 5.
Therefore, control of the gap period is not performed as shown in FIG.
[0037]
Further, the noise removal filter means 3 is formed of a filter such as BEF (Band Elimination
Filter) which targets a single or a plurality of bands, for example, in order to attenuate all bands
containing noise. The frequency distribution of the vibration noise of the actuator portion
generated when the magnetic head 15 is accelerated or decelerated rapidly is determined in
advance, and this BEF is set so as to lower the frequency band.
Also, a plurality of BEFs may be prepared and switched for each mode in accordance with the
change characteristic (seek profile) of the acceleration / deceleration of the actuator.
[0038]
Although not shown, in the case of a seek operation in an optical disk apparatus such as a DVD
(Digital Versatile Disc), a band including vibration noise such as a tracking motor for moving a
pickup is defined by the BEF constituting the noise removal filter means 3. Try to drop it.
[0039]
If all noise frequency bands as described above are cut off by the above-described noise removal
filter means 3, voice signals in the band are also removed simultaneously, which causes a
problem that the gap period is perceived in the sense of hearing.
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Therefore, in the prior application, noise reduction is realized by suppressing the gap period
within the range exerted by the masking effect of human hearing.
[0040]
However, as described above, depending on the noise period generated, the noise period
becomes longer than the gap period to be masked, which causes a problem that a partial period
of the noise signal can not be removed.
Therefore, in the present embodiment, an interpolation signal is generated within the gap period
and added by the adder 21 so that the masking effect is enhanced in terms of hearing.
[0041]
First, an example of signal interpolation in the gap period will be described with reference to FIG.
Here, a level envelope (hereinafter referred to as a level envelope) is formed so as to maintain the
continuity of the levels of the signal A and the signal B in the gap period, and an interpolation
signal is generated like a hatched portion in the gap period. The addition by the adder 21
prevents a gap from being felt in hearing.
[0042]
That is, in the example of FIG. 1, an interpolation signal is generated by the interpolation signal
generation means 22 described later, and the signal has the inverse filter characteristic of the
noise removal filter means 3, that is, the stop band is the pass band and conversely the pass band
is Through the inverse filter means 23 having a band characteristic, the level modulation means
24 further modulates the level and inputs it to the adder 21.
Further, the level envelope of the signal input from the microphone 1 is continuously detected by
the level envelope detection unit 25, and the coefficient generation unit 26 detects the level
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envelope of the input signal according to the detection level. During the gap period, level
modulation coefficients are generated continuously as in the interpolation signal of FIG.
[0043]
Here, the interpolation signal generating means 22 will be described with reference to FIG.
Here, tone signal generating means 41 for generating a signal composed of a single or a plurality
of sine waves or pulse waves of a predetermined cycle, and an M-sequence signal for generating
a white noise signal having a uniform level in all voice bands. A signal obtained by mixing the
output signal from the generating means 42 at a predetermined ratio by the mixing means 43 is
output from the output terminal 44 to be used as an interpolation signal.
[0044]
This is because a general audio signal is composed of a tone signal having a single or a plurality
of peaks at a predetermined frequency in a frequency characteristic, and a random signal
relatively flat in a frequency characteristic. As for the ratio, the mix ratio is appropriately
optimized by the noise removal band characteristic by the noise removal filter means 3. However,
even if only one random signal from the M-sequence signal generating means 42 is used with
either one set to zero. good.
[0045]
Further, with reference to FIG. 4, an example of envelope detection of the level envelope
detection means 25 will be described.
First, the arbitrary input waveform in FIG. 4A is converted into an absolute value as in FIG. 4B,
and then only low frequency components are extracted using a low pass filter (LPF) or the like
and smoothing is performed, as in thick lines in FIG. 4C. Is detected.
By the way, in the example of FIG. 1, the instantaneous noise signal in the gap period included in
the audio signal is also envelope-detected, but due to the above-mentioned smoothing, rapid level
change such as instantaneous noise is caused by the action of the low pass filter (LPF). Almost no
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envelope detection.
[0046]
By the way, the changeover switch 4 in the example of FIG. 1 may be replaced with the cross fade
changeover switch described in FIG.
In the block example of FIG. 5A, the THR input terminal 31 corresponds to one fixed contact 4a
of the changeover switch 4, and the COM input terminal 32 corresponds to the other fixed
contact 4b of the changeover switch 4. The two components are combined by the adder 37 via
the attenuator (hereinafter referred to as ATT) 34 and ATT 35 and output from the output
terminal 38.
Further, the noise timing signal 12 is input from the input terminal 33, the control coefficient
generation circuit 39 generates a control coefficient of the ATT 34, and the ATT 35 is controlled
via the coefficient inverting circuit 36. Here, when control is performed as in the timing control
example of FIGS. 5B and 5C, the output is switched by the ATT 34 at a predetermined time
constant by the control coefficient generated by the control coefficient generation circuit 39, and
the coefficient inverting circuit 36 simultaneously. When the ATT 35 is controlled by the control
coefficient of the inverse characteristic inverted at step, the output is switched to cross fade with
a predetermined time constant as shown by a solid line and a broken line, so overshoot or
ringing does not occur, and switching is further performed. Since the discontinuities of the
waveform of the THR signal and the COM signal at the time are absorbed audibly, there is an
advantage of acting on the masking effect. The state of signal interpolation at this time is shown
as an example of signal interpolation in FIG.
[0047]
Next, another example of the best mode for carrying out the audio signal noise reduction device
of the present invention will be described with reference to FIG. In FIG. 7, portions corresponding
to FIG. 13 are denoted by the same reference numerals, and the detailed description thereof is
omitted. In FIG. 7, a signal in which a noise signal from a noise generation source is mixed into an
audio signal is output from the microphone 1, but as in FIG. 13, the audio signal from the
microphone 1 is output as it is during non-impact The movable contact 4c of the changeover
switch 4 is controlled to be connected to one fixed contact 4a, and the movable contact 4c of the
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changeover switch 4 is connected to the other fixed contact 4b only when an impact to be a
target is detected by the sensor 18 Control to connect to and shut off the noise signal.
[0048]
When an audio signal is also input at the same time, this audio signal is also blocked. Here, the
level of the input audio signal is continuously detected by the level envelope detection means 25
and the masking amount is determined from this level. Interpolation signal generation means 22
and inverse filter means configured in the same manner as in the example of FIG. 1 according to
this masking amount after determining the masking amount to be masked in human auditory
sense by means 28. The level modulation unit 24 generates a level coefficient for performing
level modulation on the interpolation signal generated from the reference numeral 23 and
outputs the level coefficient to the adder 21.
[0049]
Here, an example of signal interpolation in the gap period in FIG. 7 will be described with
reference to FIG.
This example of FIG. 7 corresponds to compensating for the deficiency (ΔS in FIG. 11) in the
audibility level during the gap period with another signal in consideration of the masking action
at the audibility level shown in FIG. By generating an interpolation signal within the gap period of
FIG. 8 like a hatched portion, for example, and adding it by the adder 21, the gap is not felt in the
sense of hearing. Further, in FIG. 8, it is not necessary to ensure the continuity of the levels of the
signal A and the signal B as shown in FIG. 2, and level interpolation is performed so that the gap
period is masked in the sense of hearing.
[0050]
The changeover switch 4 of FIG. 7 may be replaced with the crossfade changeover switch
described in FIG. 5 as in the example of FIG.
[0051]
Here, the operation of the audio signal noise reduction device in FIG. 7 will be described with
reference to FIG.
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FIG. 9A shows an example of the target noise signal, and a shock noise signal as illustrated is
input from the microphone 1. Further, assuming that shock noise is detected by the sensor 18 as
shown in FIG. 9B at the same timing as this, the comparator 20 compares it with the reference
level from the input terminal 9. Then, as shown in FIG. 9C, a timing period in which the level is
larger than the reference level is taken as a noise removal period, and is supplied as the noise
timing signal 12 to the switch 4 to insert an interpolation signal.
[0052]
Next, referring to FIG. 10, still another example of the best mode for implementing the audio
signal noise reduction device of the present invention will be described. In the example of FIG.
10, parts corresponding to the examples of FIG. 1 and FIG.
[0053]
In the examples of FIGS. 1 and 7, in consideration of the masking conditions (3) and (4) described
above, the gap period is level-modulated by the interpolation signal so as to satisfy the continuity
in the level direction. In the example of FIG. 10, in addition to this, in consideration of the
masking condition (1), the gap period is frequency-modulated by the interpolation signal so as to
satisfy the continuity in the frequency direction. This can further increase the masking effect.
[0054]
First, as in FIG. 12, the noise timing signal 12 from the DSP built-in microcomputer 10
controlling the HDD is directly used as a control signal of the changeover switch 4 and at the
seek operation the movable contact 4c of the changeover switch 4 is connected to the other fixed
contact 4b. Control to select the signal from the adder 54, otherwise control to connect the
movable contact 4c of the changeover switch 4 to one of the fixed contacts 4a to select the audio
signal from the microphone 1, and the output terminal Output from 5
[0055]
Further, the noise removal filter means 3 is configured in the same manner as in the example of
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FIG. 1 so as to drop all bands containing noise, and similarly, the interpolation signal generation
means 22 and the inverse having inverse filter characteristics of the noise removal filter means 3
The interpolation signal from the filter means 23 is added by the adder 54 through the variable
filter means 53 and the level modulation means 24 which do not limit the order of processing.
Here, the level modulation means 24 is a coefficient generated by the level envelope detection
means 25 and the coefficient generation means 26 in the same manner as in FIG. 1 to
continuously detect the level envelope, and this gap period is as shown in FIG. Level modulation
continuously.
[0056]
Further, the spectrum envelope detection means 51 detects the level of each frequency of the
input signal by means of a fast Fourier transform (FFT) means or a plurality of band division
means in order to continuously detect the frequency spectrum of the input signal At 52, the
variable filter means 53 generates filter coefficients so as to reproduce the detected frequency
spectrum. This makes it possible to further increase the masking effect because the gap period is
continuously interpolated not only at the level but also at the frequency component. The level
envelope detection means 25 and the coefficient generation means 26 may be replaced with the
level envelope detection means 25 and the masking amount determination means 28 of FIG. 7
and the levels may be interpolated as shown in FIG. The changeover switch 4 may be replaced
with the cross fade changeover switch of FIG.
[0057]
The prior application Japanese Patent Application No. 2004-117248 (Noise reduction method
and apparatus) is a noise reduction method in which only the noise occurrence period is simply
gated using human auditory masking, but in this example, the gap period is separately Since the
level envelope interpolation is performed on the signal generated in the above, it is possible to
reduce noise that has continued for a longer time.
[0058]
Further, according to the present embodiment, in consideration of temporal masking in human
auditory masking, the lack of effective masking during the gap period is interpolated, so that
long-lasting noise can be reduced.
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[0059]
According to this embodiment, it is effective in removing click noise and shock noise included in
the audio signal in general, and in particular, it is effective in noise generated in a small device
such as a built-in microphone.
[0060]
According to this example, a sensor is used as a method of detecting a noise generation period,
and a period with a large noise level is extracted.
For example, if the sensor is placed near a noise source, noise can be easily detected, and a
plurality of sensors can be prepared to improve detection accuracy.
Further, by adjusting the reference level in the comparator, the timing with the largest noise level
can be detected and removed, and the removal effect can be increased even when the gap period
is short.
[0061]
Further, according to the present embodiment, when the noise generation source is controlled by
the microcomputer or the like as in the seek noise generated from the disk device, for example,
the noise timing information is present, so the sensor or the like is not used. However, the noise
generation period can be easily limited.
[0062]
According to this example, even if the gap period is removed only by the noise band filter and the
voice signal is completely removed together with the noise, no problem occurs because the gap
period is interpolated so as to be masked by auditory sense. .
Moreover, since continuity is maintained in the band signal other than the noise band before and
after the gap period, there is an advantage that the gap time to be masked can be long.
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[0063]
According to this example, the audio signal is a composite signal of a plurality of sine waves, but
in order to reproduce this, the audio signal can be generated relatively easily by combining the
repetitive periodic signal and the random signal.
Further, in this example, it is not necessary to faithfully reproduce the audio signal, and the
signal interpolation is performed so as to compensate for the sense of deficiency in the gap
period and to satisfy the masking condition.
[0064]
According to this embodiment, overshoot and ringing do not occur when switching between the
normal time and the gap period, and there is an advantage that the masking effect is
advantageously performed because the wide band due to the generation of harmonic noise does
not occur.
[0065]
According to this embodiment, by changing not only the level modulation but also the frequency
characteristic of the signal to be interpolated in the gap period, it is possible to maintain the
continuity of the signal and to further increase the masking effect.
[0066]
Although the above example has been described with a single channel by one microphone, it can
be easily understood that the same configuration can be made for a plurality of channels of two
or more channels.
[0067]
Further, the present invention is not limited to the above-described example, and it goes without
saying that various other configurations can be adopted without departing from the scope of the
present invention.
[0068]
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FIG. 1 is a configuration diagram showing an example of a best mode for implementing an audio
signal noise reduction device of the present invention.
FIG. 2 is a diagram for describing the present invention.
It is a block diagram which shows the example of an interpolation signal generation means.
FIG. 2 is a diagram for describing the present invention.
A figure is the block diagram which shows the example of the cross fade changeover switch, B
figure and C figure oscillation frequency The figure which is offered to the explanation. FIG. 2 is a
diagram for describing the present invention. It is a block diagram which shows the other
example of the best form for implementing this invention audio signal noise reduction apparatus.
FIG. 2 is a diagram for describing the present invention. FIG. 2 is a diagram for describing the
present invention. It is a block diagram which shows the further another example of the best
form for implementing this invention audio signal noise reduction apparatus. FIG. 2 is a diagram
for describing the present invention. It is a block diagram which shows the example of an audio |
voice signal noise reduction apparatus. It is a block diagram which shows the other example of
an audio | voice signal noise reduction apparatus.
Explanation of sign
[0069]
DESCRIPTION OF SYMBOLS 1 ... Microphone 2, 19 ... Amplifier, 3 ... Noise removal filter means, 4
... Switching switch, 5 ... Output terminal, 9 ... Reference level input terminal, 10 ... DSP built-in
microcomputer, 12 ... Noise timing signal, 18 ... Sensor, 20: comparator, 21, 54: adder, 22:
interpolation signal generation means, 23: inverse filter means, 24: level modulation means, 25:
level envelope detection means, 26, 52: coefficient generation means, 28: masking amount
determination Means, 51: Spectrum envelope detection means, 53: Variable filter means
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