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JP2005328320

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JP2005328320
PROBLEM TO BE SOLVED: To provide a "noise removing device" capable of reliably removing
noise included in an unnecessary band regardless of the content of a signal and eliminating a
sense of discomfort given to a user. SOLUTION: A frequency characteristic analysis unit 60 which
analyzes a frequency characteristic of audio data and determines a lower limit frequency and an
upper limit frequency of a frequency band having a signal level equal to or higher than a
reference value; A digital filter 38 is provided which passes components of the frequency band
sandwiched between the upper limit frequencies. [Selected figure] Figure 1
Noise removal device
[0001]
The present invention relates to a noise removing device used for an audio device or the like.
[0002]
2. Description of the Related Art Conventionally, an audio apparatus has been known which
analyzes the frequency characteristics of an audio signal to automatically set the equalizer (see,
for example, Patent Documents 1 and 2).
In these audio devices, it is determined whether the content of the audio signal corresponds to
vocals or to instrumental music to set the equalizer, or the music corresponding to the audio
signal is classical, jazz or pop The equalizer setting may be performed by determining which of
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the two is the case. Thus, the user does not have to manually change the setting of the equalizer
each time the content of the audio signal changes, and the operability can be improved. JP-A-1195759 (page 3-6, FIG. 1-5) JP-A-2001-85962 (page 3-5, FIG. 1-4)
[0003]
By the way, in the above-described conventional audio apparatus, the contents of the audio signal
are analyzed and the setting of the equalizer according to the frequency characteristic is made, so
the gain for each frequency band is set according to the type of the audio signal. Since setting of
the equalizer according to the presence or absence of each frequency band component is not
performed, there has been a problem that noise outside the voice band etc. can not be sufficiently
reduced. For example, if it is determined that the result of analyzing the content of the audio
signal corresponds to the vocal, the gain of each frequency band component corresponding to
the vocal is set to a predetermined value, but each frequency corresponding to the vocal It is
desirable to remove unnecessary components such as noise included in the outside of the band.
However, since there is wide and narrow frequency bands corresponding to vocals depending on
vocal bands, which are different for women / males, and even the same female or male voice
band, unnecessary components such as noises outside this frequency band Can not be
completely removed. Also, in the above-described conventional audio apparatus, it takes a certain
amount of time to analyze the contents of the audio signal and change the setting of the
equalizer, so the settings of the equalizer are actually changed after the contents of the audio
signal are switched. There was a time lag, which made the user who is listening to the audio
sound uncomfortable.
[0004]
The present invention has been made in view of such a point, and an object thereof is to be able
to reliably remove the noise contained in the unnecessary band regardless of the content of the
signal, and to give a sense of discomfort to the user. It is providing the noise removal apparatus
which can be eliminated.
[0005]
In order to solve the problems described above, the noise removal apparatus according to the
present invention analyzes the frequency characteristics of the audio signal and determines a
lower limit frequency and an upper limit frequency of a frequency band having a signal level
higher than a reference value. And a filter for passing a component of a frequency band
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2
sandwiched between the lower limit frequency and the upper limit frequency when an audio
signal is input.
Since the frequency characteristics of the audio signal are analyzed to determine the lower limit
frequency and the upper limit frequency at which the signal component exists and only the
frequency band component sandwiched between them is extracted, noise included in
unnecessary bands regardless of the content of the signal Can be reliably removed.
[0006]
Further, it is desirable to further include reference value setting means for setting the reference
value used in the analysis of the frequency analysis means described above in accordance with
the operation instruction by the user. This makes it possible to remove noise that reflects user
preferences that can not be automatically set.
[0007]
The memory control means is further provided with a memory control means for temporarily
storing digital data corresponding to the above-mentioned audio signal in the memory and then
reading out the data, and the frequency analysis means analyzes the frequency of the audio
signal using the digital data stored in the memory It is desirable to perform processing to pass
frequency band components to digital data read from the memory. By this, even if the content of
the audio signal changes, the lower limit frequency and the upper limit frequency are determined
without delay, and noise in the frequency band out of these is accurately followed by the content
of the audio sound to be output. It is possible to remove it, and it is possible to eliminate the
sense of discomfort to the user.
[0008]
The memory described above is preferably a shock proof memory provided to prevent sound
skipping in an audio apparatus having a movable part. By using a shockproof memory, it is not
necessary to add memory just to realize analysis of frequency characteristics and real-time
processing according to the contents of audio signal, so the configuration can be simplified and
the cost can be reduced accordingly. become.
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[0009]
Further, the above-mentioned frequency analysis means determines that the lower limit
frequency and the upper limit frequency determined before when the digital data stored in the
shock proof memory becomes smaller than the amount of data required for analysis by the
frequency analysis means. It is desirable to maintain the value. As a result, excessive vibration is
applied to the audio device to reduce the amount of data stored in the shockproof memory
before reading, which makes it difficult to analyze the frequency characteristics, and noise is
removed with the previous setting. As a result, noise can be prevented from increasing suddenly
and discomfort can be prevented.
[0010]
Hereinafter, a disc reproducing apparatus as an audio apparatus according to an embodiment to
which the noise removing apparatus of the present invention is applied will be described in detail
with reference to the drawings.
[0011]
FIG. 1 is a view showing the configuration of a disc reproducing apparatus according to an
embodiment to which the present invention is applied.
As shown in FIG. 1, the disk reproducing apparatus 1 according to this embodiment includes a
spindle motor 12, an optical pickup 14, a feed motor 16, a servo circuit 18, a disk loading
detection unit 20, an RF amplifier 30, a digital signal processing circuit 32, a shock. A proof
memory 34, a shock proof memory controller 36, a digital filter 38, a D / A (digital-analog)
conversion circuit 40, a system controller 50, an operation unit 52, and a frequency
characteristic analysis unit 60 are included.
[0012]
The spindle motor 12 rotates a CD (compact disc) 10 at a predetermined linear velocity. The
optical pickup 14 detects a signal recorded on the CD 10, and includes a semiconductor laser and
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a photodiode. The feed motor 16 moves the optical pickup 14 in the radial direction of the CD
10. The servo circuit 18 drives the spindle motor 12 and the feed motor 16 and moves the focus
position of the semiconductor laser in the direction perpendicular to the recording surface of the
CD 10 by moving the focus lens (not shown) incorporated in the optical pickup 14 Let The servo
circuit 18 also performs various servo (focus servo, tracking servo, rotational servo) control
necessary for reading a recording signal from the CD 10. The disc loading detection unit 20
detects that the CD 10 has been loaded.
[0013]
The RF amplifier 30 creates an EFM (Eight to Fourteen Modulation) signal, a focus error signal, a
CLV (Constant Linear Velocity) control signal, and the like based on the detection signal of the
optical pickup 14, and It also has a function of outputting a track jump detection signal when a
track jump occurs due to vibration, shock or the like. The digital signal processing circuit 32
performs synchronous detection and EFM demodulation on the signal output from the RF
amplifier 30, and then performs CIRC (Cross Interleaved Reed-Solomon Code) decoding
processing to output digital audio data. . The audio data in the present specification includes data
of only human voice, in addition to data recorded when playing an instrument or the like.
[0014]
The shock proof memory 34 is for temporarily storing digital audio data output from the digital
signal processing circuit 32, and generally, a DRAM is used. The shockproof memory controller
36 controls reading and writing of data to the shockproof memory 34. The shockproof memory
controller 36 writes the audio data output from the digital signal processing circuit 32 to the
shockproof memory 34, and the written audio The operation of reading data at a constant speed
is performed in parallel. The shockproof memory controller 36 also notifies the system controller
50 whether the amount of data before read stored in the shockproof memory 34 is greater than
or equal to a predetermined amount. As the predetermined amount, the minimum value of the
data amount that allows the frequency characteristic analysis unit 60 to analyze the frequency
characteristic is used (or a value larger than this minimum value may be used with some margin)
.
[0015]
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The digital filter 38 extracts only valid signal components from the audio data read from the
shockproof memory 34 under the control of the shockproof memory controller 36. The lower
limit frequency and the upper limit frequency of the pass band necessary for the signal
component extraction are variably set according to the contents of the audio data. In order to
perform this band pass processing, the digital filter 38 is formed by combining a high pass filter
in which the lower limit frequency of the pass band is set as the cutoff frequency and a low pass
filter in which the upper limit frequency of the pass band is set as the cutoff frequency. It has
been realized. The D / A conversion circuit 40 converts audio data input through the digital filter
38 into an analog signal to reproduce music. The reproduced analog signal is amplified by an
audio amplifier (not shown) and output from the speaker.
[0016]
The system controller 50 outputs various servo commands to the servo circuit 18, or receives
and analyzes TOC (Table of Contents) information and other sub code data etc. output from the
digital signal processing circuit 32. Perform various controls necessary for music playback. In
particular, the system controller 50 sets the minimum frequency and the maximum frequency of
the pass band of the digital filter 38. Further, when the track jump detection signal is input from
the RF amplifier 30, the system controller 50 stores the absolute time included in the Q channel
data in the sub code input from the digital signal processing circuit 32 at that time in the built-in
memory. At the same time, a track jump occurrence notification is issued to the shockproof
memory controller 36, and then return control is performed to return the optical pickup 14 to
the position before the jump, and a return notification is output to the shockproof memory
controller 36 after completion of the return. Do. The operation unit 52 is for the user to input an
operation instruction, and includes various key switches, volume knobs, and the like.
[0017]
The frequency characteristic analysis unit 60 analyzes the frequency characteristic based on the
audio data written in the shockproof memory 34 by the shockproof memory controller 36, and
determines the lower limit frequency and the upper limit frequency of the frequency band
including the effective signal component. Do. For example, analysis of frequency characteristics is
performed by performing fast Fourier transform processing using a predetermined number of
audio data to detect the signal level of each frequency component, and check whether each
signal level is equal to or higher than a reference value. Thus, the minimum value of the
frequency band having the signal level equal to or higher than the reference value is determined
as the minimum frequency, and the maximum value is determined as the maximum frequency.
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The reference value is variably set by the system controller 50 in accordance with the user's
instruction. The user can indicate the level of the reference value using the operation unit 52 (for
example, any of the plurality of stages can be selected with the UP / DOWN key, the arrow key,
etc.), and the system controller 50 Set a reference value according to this instruction.
[0018]
For example, the digital signal processing circuit 32 described above, the shock proof memory
34, the shock proof memory controller 36, the digital filter 38, the D / A conversion circuit 40,
and the frequency characteristic analysis unit 60 are implemented by DSP (digital signal
processing device) for audio processing. It has been realized. Further, the above-described
frequency characteristic analysis unit 60 corresponds to the frequency characteristic analysis
unit, the system controller 50 corresponds to the reference value setting unit, and the shockproof
memory controller 36 corresponds to the memory control unit.
[0019]
The disk reproducing apparatus 1 of the present embodiment has such a configuration, and its
operation will be described next.
[0020]
FIG. 2 is a flow chart showing an operation procedure for automatically setting the
characteristics of the digital filter 38 based on the contents of audio data in the disk reproducing
apparatus 1 of the present embodiment.
The system controller 50 determines whether or not the CD 10 is loaded by monitoring the
detection result of the disc loading detection unit 20 (step 100), and repeats this determination
until the CD 10 is loaded. When the CD 10 is loaded, a positive determination is made in step
100, and then the system controller 50 sends an instruction to the servo circuit 18 to drive the
feed motor 16 to bring the optical pickup 14 near the inner periphery of the CD 10. The signal is
moved to read the signal recorded in the area of the lead-in, and the TOC information contained
in the lead-in is stored in the built-in memory (step 101). Then, the system controller 50 starts
reproduction from the beginning of the first music recorded on the CD 10 based on the read TOC
information (step 102). Specifically, the system controller 50 sends an instruction to the servo
circuit 18 to drive the feed motor 16 to move the optical pickup 14 to the top position of the first
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CD of the CD 10, and the servo circuit 18 causes the spindle motor 12 to Rotate at double speed
or more. After that, the recording signal is read from the CD 10 at double speed or more with the
servo circuit 18 subjected to rotational servo, focus servo and tracking servo, and the digital
signal processing circuit 32 performs predetermined demodulation processing and decoding
processing to obtain audio data Is output. The audio data is written to the shockproof memory 34
under the control of the shockproof memory controller 36. Further, in parallel with the writing
operation of the audio data, the audio data is also read from the shockproof memory 34, and the
data read by the control of the shockproof memory controller 36 is the digital filter 38 and the D
/ D /. Through the A conversion circuit 40, it is converted into an analog signal to reproduce
music.
[0021]
Further, in parallel with the reproduction operation of the audio data, the system controller 50
determines whether the data amount of the audio data before read stored in the shockproof
memory 34 has reached a predetermined amount or more (step 103). ). Immediately after the
start of reproduction, the audio data before read out stored in the shockproof memory 34 is
small, so a negative determination is made and this determination is repeated. In addition, when
the data amount of the audio data before reading exceeds the predetermined amount, an
affirmative determination is made in step 103, and then the frequency characteristic analysis
unit 60 determines the frequency based on the audio data stored in the shockproof memory 34.
The characteristics are analyzed (step 104), and the lower limit frequency and the upper limit
frequency at which the effective component of the audio data is included are determined (step
105).
[0022]
FIG. 3 is an explanatory view of the determination operation of the lower limit frequency and the
upper limit frequency. In FIG. 3, the horizontal axis corresponds to the frequency, and the vertical
axis corresponds to the signal level. When frequency characteristics as shown in FIG. 3 are
obtained as a result of the frequency characteristics analysis in step 104, the frequency
characteristics analysis unit 60 compares the signal level for each frequency component in these
frequency characteristics with the reference value R, The lower limit frequency Fmin and the
upper limit frequency Fmax of frequency components having signal levels exceeding the
reference value R are determined. As described above, the reference value R used for this
determination is variably set based on the user's instruction, and can automatically reflect
preferences that can not be set for each user.
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[0023]
The system controller 50 sets the cutoff frequency of the high pass filter included in the digital
filter 38 using the determined lower limit frequency, and sets the cutoff frequency of the low
pass filter using the determined upper limit frequency (step 106). ). Thereafter, with respect to
the audio data read out from the shock proof memory 34, processing of passing the digital filter
38 set based on the audio data is performed.
[0024]
FIG. 4 is a diagram showing frequency characteristics of audio data after passing through the
digital filter 38. As shown in FIG. In the digital filter 38, since the cutoff frequency of the high
pass filter is set to Fmin and the cutoff frequency of the low pass filter is set to Fmax, only the
frequency components included in the range from Fmin to Fmax are selectively output. Noise
components outside the range are removed.
[0025]
Next, the system controller 50 determines whether the reproduction has ended (step 107). When
all reproduction of the audio data corresponding to the last music is completed, or when
cancellation of reproduction is instructed during reproduction, a positive determination is made,
and a series of processes related to reproduction is ended. If the reproduction is not completed, a
negative determination is made in the determination of step 107, and next, the system controller
50 determines whether the data amount of the audio data before reading stored in the
shockproof memory 34 is equal to or more than a predetermined amount It is determined
whether or not it is (step 108). If the predetermined amount or more is maintained, an
affirmative determination is made, and the process returns to step 104 and the operations after
the frequency analysis processing are repeated. Further, when the data amount of the audio data
before read out stored in the shockproof memory 34 falls below the predetermined amount in
the middle of the reproduction operation, a negative determination is made in step 108, and the
system controller 50 An instruction to maintain the setting is issued (step 109), and then the
determination of step 108 is repeated.
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[0026]
As described above, in the disc reproducing apparatus 1 according to the present embodiment,
the frequency characteristic of audio data is analyzed to determine the lower limit frequency and
the upper limit frequency at which the signal component is present, and only the frequency band
component sandwiched therebetween is extracted. Therefore, regardless of the content of the
signal, noise contained in the unnecessary band can be reliably removed.
[0027]
Also, by setting the reference value used in the analysis of the frequency characteristic analysis
unit 60 according to the operation instruction by the user, it is possible to remove noise that
reflects the preference of each user that can not be set automatically.
[0028]
Further, since shock-proof memory 34 for temporarily storing audio data is provided, and
analysis of frequency characteristics is performed using the audio data stored in shock-proof
memory 34, even if the contents of the audio data change. It is possible to determine the lower
limit frequency and the upper limit frequency without delaying and remove noise in the
frequency band outside these by following the contents of the audio data to be output and
eliminating the sense of discomfort for the user be able to.
In particular, by using a shockproof memory 34 provided to prevent sound skipping in the disc
reproducing apparatus 1 as an audio apparatus having a movable part, real time processing
according to analysis of frequency characteristics and contents of audio data can be performed.
Since it is not necessary to add memory only for implementation, simplification of the
configuration and cost reduction associated therewith are possible.
[0029]
In addition, when the data amount of the audio data stored in the shock proof memory 34
becomes smaller than the data amount necessary for analysis by the frequency characteristic
analysis unit 60, the values of the lower limit frequency and the upper limit frequency
determined before that Setting of the digital filter 38 is performed, so that excessive vibration is
applied to the disk reproducing apparatus 1 and the amount of data before read stored in the
shockproof memory 34 decreases, making frequency characteristic analysis difficult. Even if this
is the case, since noise removal is continued with the previous setting, it is possible to prevent a
sudden increase in noise and an increase in discomfort.
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[0030]
The present invention is not limited to the above embodiment, and various modifications can be
made within the scope of the present invention.
Although the noise removal in the disk reproducing apparatus 1 has been described in the abovedescribed embodiment, the present invention can be applied to the noise removal in various
audio apparatuses other than the disk reproducing apparatus 1.
For example, a case may be considered in which noise is removed in a car audio apparatus or the
like in which a reproduction mechanism such as a CD or MD is integrated, or in a home stereo
apparatus.
[0031]
In the embodiment described above, the frequency characteristic analysis unit 60 and the like are
provided in the disc reproducing apparatus 1 to remove noise, but similar noise removal is
performed in an amplifier to which the disc reproducing apparatus 1 or other audio apparatus is
connected. You may do so. In this case, a dedicated memory for noise removal may be used
instead of the shock proof memory 34.
[0032]
FIG. 1 is a diagram showing the configuration of a disc reproduction apparatus according to an
embodiment. 7 is a flow chart showing an operation procedure for automatically setting the
characteristics of the digital filter based on the contents of audio data in the disc reproducing
apparatus of the present embodiment. It is explanatory drawing of determination operation |
movement of a lower limit frequency and an upper limit frequency. It is a figure which shows the
frequency characteristic of the audio data after passing a digital filter.
Explanation of sign
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[0033]
DESCRIPTION OF SYMBOLS 1 disc reproducing apparatus 12 spindle motor 14 optical pick-up
16 feed motor 18 servo circuit 30 RF amplifier 32 digital signal processing circuit 34 shock
proof memory 36 shock proof memory controller 38 digital filter 40 D / A conversion circuit 50
system controller 52 operation part 60 frequency Characteristic analysis unit
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