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JP2002199486

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JP2002199486
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
noise removing device for receiving an audio signal, and more specifically, a noise removing
device and a car radio used in, for example, a car radio etc. Audio devices, etc.
[0002]
2. Description of the Related Art For example, when electromagnetic wave noise in the
environment of a car is considered, many pulsed electromagnetic wave noises (sometimes
referred to as pulse noise) such as ignition noise and mirror noise are generated. Since these
pulsating noises are mixed in with the receiving antenna connected to the car radio inside the
vehicle, it is usually well experienced that pulsing noise is generated in the output sound signal,
and therefore, in car radios generally pulse Noise removal devices are used to remove sexual
noise.
[0003]
FIG. 9 is a block diagram of a conventional (pulsed) noise removing device described in, for
example, Japanese Patent Application Laid-Open No. 63-87026. In the figure, when the FM
intermediate frequency signal of the FM receiver is input, the detection signal output from the
FM detection circuit 1 is supplied to the delay circuit 2 composed of the LPF (low pass filter) and
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delayed, and the output of the delay circuit 2 is the gate circuit 3 Then, the signal is supplied to
the stereo demodulation circuit 5 through the level hold circuit 4. The detection signal is
supplied to an HPF (high pass filter) 6, and the noise component signal passing through the HPF
6 is amplified by the noise amplifier 7 and supplied to the noise detection circuit 8.
[0004]
The noise detection circuit 8 comprises a rectification circuit that rectifies the output signal of
the noise amplifier 7 to obtain a noise detection output. The noise detection output is supplied to
the waveform shaping circuit 9 and the integration circuit 10. The noise detection means 11 is
configured to include the HPF 6, the noise amplifier 7, the noise detection circuit 8, the
waveform shaping circuit 9, and the integration circuit 10.
[0005]
The waveform shaping circuit 9 converts the noise detection output into a pulse having a
predetermined time width and supplies the pulse to the gate circuit 3. The gate circuit 3 is driven
by the pulse supplied from the waveform shaping circuit 9 to the gate circuit 3 to be in the signal
blocking state, and in the signal blocking state, the level hold circuit 4 holds the delayed output
level before the signal blocking and the stereo demodulation circuit It is supplied to 5.
[0006]
This prevents the generation of spike noise due to a sudden change in the potential of the
demodulation signal due to the pulsating noise. When no pulse is supplied from the waveform
shaping circuit 9, the gate circuit 3 and the level hold circuit 4 are in a signal passing state
(through).
[0007]
Further, the integration circuit 10 smoothes the noise detection output to obtain a DC signal
according to the noise level, and provides the output of the integration circuit 10 to the noise
amplifier 7 (feedback) to form an AGC loop.
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[0008]
The delay circuit 2 is provided to compensate for the time from the pulse noise being supplied to
the HPF 6 to the gate circuit 3 being turned off.
Further, as shown in FIG. 10, the Lch (left channel) signal and the Rch (right channel) signal are
input to the stereo demodulation circuit 5 in the form of balanced modulation at a frequency of
38 kHz centered on (Lch + Rch) / 2. For example, Lch signals and Rch signals can be separated
and taken out by time division at 38 kHz, for example (Lch signals, Rch signals, or stereo signals
of Lch signals and Rch signals are collectively referred to as audio signals).
[0009]
In addition to the above-described level holding and output of the previous signal, there is also a
method of correcting the level before and after the occurrence of pulse noise with an average
value or the like. By the way, this method has the following problems.
[0010]
FIG. 11A shows a waveform in the case where the correction error obtained by correcting the low
frequency signal with respect to the correction period is the largest. In the figure, the ○ marks
are values obtained by correcting the 印 marks, and the difference between the 印 marks and the
印 marks indicates a correction error.
[0011]
Next, FIG. 11B shows a waveform in the case of correcting a signal of a high frequency with
respect to the correction period. The circle marks in the same figure indicate the values obtained
by correcting the circle marks. Similar to FIG. 11 (a), the difference between ● and 印 indicates a
correction error.
[0012]
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Here, looking at each correction error, FIG. 11 (b) is larger. That is, the relationship of the relative
time width of the frequency to the correction period is very important, and it can be understood
that the error is large even if the signal of the high frequency component is corrected. Therefore,
even if correction is performed on a signal containing many high frequencies, a correction error
can be heard as noise. Here, when the pulse width of the pulse noise is several tens μs to several
hundreds μs, as shown in FIG. 10, the composite signal has a balanced modulation component at
38 kHz as shown in FIG. A correction error such as (b) occurs.
[0013]
SUMMARY OF THE INVENTION In view of this point, the present invention has an object to
obtain a noise eliminator having an improved noise suppression capability, which can reduce the
correction error even for a signal containing many high frequency components.
[0014]
A noise removing apparatus according to the present invention comprises a noise detecting
means for detecting noise contained in an FM demodulated signal, an audio signal demodulating
means for demodulating an audio signal contained in the FM demodulated signal, and A first
correction that receives the audio signal output from the audio signal demodulation means as an
input, and outputs a correction signal of the audio signal based on the audio signal before and
after the generation time of noise detected by the noise detection means Means and the audio
signal output from the audio signal demodulation means are input, and predetermined
processing is performed on at least one of the audio signals before or after the generation time of
the noise detected by the noise detection means Second correction means for outputting a
correction signal of the audio signal based on the signal; and the audio signal A high band level
detecting means for detecting the level of the high band component of the audio signal output
from the adjusting means, and either the first or second correcting means is selected based on
the output of the high band level detecting means And selecting means.
[0015]
Further, the first correction means is characterized in that a low pass filter output of a signal
value obtained from linear interpolation of two signal values present immediately before and
after a noise generation time point is output as a correction signal.
[0016]
Further, the signal value obtained by holding the low-pass filter output of the audio signal output
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from the audio signal demodulation means just before the point of occurrence of noise in the
audio signal is set as a correction signal by predetermined processing in the second correction
means. It is characterized by being.
[0017]
Further, the second correction means can be obtained from linear interpolation of two average
signal values obtained by averaging a plurality of signal values respectively existing before and
after the noise generation time point corresponding to the noise generation time. A low pass
filter output of the signal value is used as a correction signal.
[0018]
The signal processing apparatus further comprises level detection means for detecting the level
of the entire band in the demodulated audio signal, and selection is made based on the ratio of
the level output of the high band level detection means to the level output of the level detection
means and a predetermined value. Operating the means.
[0019]
Also, the noise detection means is characterized in that the detection sensitivity is variable
according to the output level of the high band level detection means.
[0020]
Further, the FM demodulation signal is input to the first correction means and the second
correction means, and selection is made based on the level of the addition signal and the level of
the subtraction signal between the right channel signal and the left channel signal constituting
the audio signal. Operating the means.
[0021]
An audio apparatus according to the present invention includes the noise removal apparatus
described in any of the above.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION By applying the present invention to an audio
output device such as a car audio device such as a car radio, a car video device such as a carmounted television, or an audio-video device including this audio output device, for example. An
embodiment of a configuration capable of exerting a significant effect on noise removal will be
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described.
[0023]
The present invention will be specifically described below based on the drawings showing the
embodiments thereof.
Embodiment 1
FIG. 1 is a block diagram of a noise eliminator according to a first embodiment of the present
invention.
[0024]
Reference numeral 1000 is an FM demodulator for demodulating an FM signal from received
broadcast waves, etc., 5 is a stereo demodulation means, 12 is a correction means for medium to
low frequency band signals for Rch of the stereo demodulation means 5, 13 is High frequency
band correction means for Rch of stereo demodulation means 5, 21 is a switch for switching the
output signals of high frequency band correction means 13 and middle low frequency band
correction means 12, 14 is Lch of stereo demodulation means 5 Medium-low range correction
means for middle-low range signals (here, the middle-low range correction means 12 and 14 are
first correction means provided corresponding to Rch and Lch, respectively).
[0025]
15 is a high frequency band correction means for the Lch high frequency signal of the stereo
demodulation means 5, 22 is a switch for switching the output signals of the high frequency
band correction means 15 and the medium low frequency band correction means 14, 16 is an
output signal of the switch 21 Level detection means for detecting the level (envelope) and high
band level detection means for detecting the high band component of the output signal of the
switch 21 (here, the high band correction means 13 and 15 are Rch and Lch, respectively) And
second correction means provided corresponding to
[0026]
The reference numeral 18 denotes a level detection means for detecting the level of the output
signal of the switch 22, 19 denotes a high band level detection means for detecting a high band
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component of the output signal of the switch 22, 200 denotes the level detection means 16 and
the high band level detection means 17. Selection means for controlling the switch 21 to each
output level, 201 is selection means for controlling the switch 22 in accordance with the
respective output levels of the level detection means 18 and the high band level detection means
19.
[0027]
Next, the operation will be described.
For example, in a car radio as an example of the audio output device described above, the FM
demodulator 1000 outputs an FM demodulated signal from the received broadcast signal by an
attached antenna or the like.
The FM demodulation signal is input to the stereo demodulation circuit 5 and the noise detection
means 110, and subjected to the processing described in detail below.
[0028]
First, the noise detection means 110 detects pulse noise in the same manner as, for example, the
noise detection means 11 in the conventional device.
As an output signal of the noise detection means 110, a high level (H level) is output in a period
in which pulse noise is detected, and a low level (L level) gate signal is output in a period not
detected. It is input to the range correction means 13, the middle low range correction means 12,
the high range correction means 15, and the middle low range correction means 14.
[0029]
Next, each correction means 12-15 corrects the input signal (output from the stereo
demodulation means 5) in the period in which the gate signal is at the H level, and outputs the
input signal as it is in the period in the L level.
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[0030]
(Regarding correction with values before and after the correction period) Here, the middle and
low band correction means 12 and 14 use the values before and after the correction period to
signal the signal during a noise generation period (hereinafter referred to as noise period). Linear
interpolation is performed (a signal output by this linear interpolation is called a correction
signal).
The correction signal may be output via a low pass filter.
[0031]
As a result of linear interpolation of a signal with a long wavelength (that is, a low frequency)
with respect to the noise period using the medium / low band correction means 12 and 14, the
correction error becomes the largest and the wavelength with respect to the noise period. FIG. 2
shows an example of a waveform in which the correction error is the largest as a result of linear
interpolation of a short signal (ie, high frequency).
[0032]
The black circles in FIG. 2 represent the level that should be obtained in the absence of noise, and
in this case, correspond to the point at which the correction error becomes the largest, and the
black circles indicate the correction value (middle low The correction value by the correction
means 12 is shown.
[0033]
FIG. 2A shows the case where the wavelength of the output signal of the stereo demodulation
means 5 is long with respect to the correction period (that is, the frequency is low with respect to
the correction period), and the level difference (difference ) Is small, and the error due to the
correction is very small or hardly with respect to the amplitude of the signal waveform.
As described above, the first correction means outputs a correction signal for correcting noise
based on signal values existing immediately before and after a predetermined period including a
noise generation time (in each of the following embodiments). The same operation is performed
for the first correction means in the description unless otherwise noted.
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[0034]
FIG. 2 (b) shows the case where the wavelength of the output signal of the stereo demodulation
means 5 is short with respect to the correction period (that is, the frequency is high with respect
to the correction period). And the error due to the correction is large relative to the amplitude of
the signal waveform.
[0035]
That is, when performing interpolation using the above-described medium-low range correction
means 12 on a signal waveform having a short wavelength of the signal waveform (that is, a
signal waveform of high frequency), a sufficient noise suppression effect can not be obtained. It
will be.
[0036]
Next, the high frequency band correction means 13 and 15 perform averaging processing before
and after the correction period (the symbol ◆ indicates the average value in the average period),
and Linear interpolation is performed using the average value (average signal value as a
correction signal).
The correction signal (average signal value) is output through a low pass filter.
[0037]
Here, the average period is a predetermined period before and after the noise period, and based
on a plurality of signal values included in the period, an average value of signal levels in the
period is determined.
[0038]
FIG. 2 shows waveforms obtained by correcting the low frequency and high frequency signals
with respect to the correction period using the high frequency band correction means 13 and 15.
[0039]
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FIG. 2 (a) shows the case where the wavelength of the output signal of the stereo demodulation
means 5 is long with respect to the correction period (that is, the frequency is low with respect to
the correction period). Is smaller than the ○ mark.
[0040]
FIG. 2 (b) shows the case where the wavelength of the output signal of the stereo demodulation
means 5 is longer than the correction period (that is, the frequency is lower than the correction
period), and the level difference with .circle-solid. Is smaller than ▽ mark.
[0041]
Therefore, when the wavelength of the signal waveform is sufficiently long with respect to the
correction period (that is, the frequency of the signal waveform is lower than the correction
period), correction (interpolation processing) is performed using the middle and low band
correction means 12 and 14. If the wavelength of the signal waveform is short with respect to
the correction period (that is, it is high with respect to the frequency correction period of the
signal waveform), correction (interpolation processing) is performed using the high frequency
band correction means 13 and 15.
As described above, the second correction means outputs a correction signal for correcting noise
based on a plurality of signal values present immediately after a predetermined period including
a noise generation time (in each of the following embodiments). The same operation is performed
for the second correction means in the description unless otherwise noted.
[0042]
(Regarding Level Detection Means) Next, the level detection means will be described (in the
following, first, the configuration related to the Rch sequence will be described in order to
simplify the understanding).
[0043]
The level detection means 16 detects the level of the signal corrected using the high frequency
correction means 12 or the middle low frequency correction means 13 (envelope detection).
[0044]
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The level detection means 16 in this case can be realized, for example, by adopting a
configuration as shown in FIG. 3 (a).
Here, it is assumed that the output of the switch 21 does not include the DC component.
[0045]
In the figure, 23 is an absolute value circuit, and 24 is a low pass filter (LPF).
First, in the absolute value circuit 23, the absolute value of the output signal output from the
switch 21 is determined, and the high frequency component is removed by the LPF 24.
The output signal of the LPF 24 is output as an envelope of the signal output from the switch 21.
[0046]
Also for the Lch series, the level detector 18, the high band correction means 15 or the middle
low band correction means 14, and the switch 22 respectively correspond to the Rch, and the
structure of the level detector 18 is also shown in FIG. The same one as shown in is adopted, and
the operation is also the same.
[0047]
(Regarding High Frequency Level Detecting Means) Next, the high frequency level detecting
means will be described (in the following, first, a configuration related to the Rch sequence will
be described in order to simplify the understanding).
[0048]
The high frequency level detection means 17 detects the level of the signal corrected using the
high frequency correction means 12 or the middle low frequency correction means 13 (envelope
detection).
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[0049]
The high band level detection means 17 in this case can be realized, for example, by adopting a
configuration as shown in FIG. 3 (b).
Here, it is assumed that the output of the switch 21 does not include the DC component.
[0050]
In the figure, 25 is a high pass filter (HPF), 26 is an absolute value circuit, and 27 is a low pass
filter (LPF).
First, in the HPF 25, high frequency components are obtained except for the low frequency
components of the output signal output from the switch 21.
[0051]
Next, the absolute value circuit 26 obtains the absolute value of the output signal of the HPF 25.
Next, the LPF 27 removes high frequency components.
The output signal of the LPF 27 is output as an envelope of high frequency components of the
signal output from the switch 21.
[0052]
In the Lch sequence, the high frequency level detection means 19, the high frequency correction
means 15 or the middle low frequency correction means 14, and the switch 22 respectively
correspond to the Rch, and the high frequency level detector 19 is also illustrated. The same one
as shown in 3 (b) is adopted, and the operation is also the same.
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[0053]
Next, the selection means 200 will be described.
The output signal VH from the high band level detection unit 17 and the output signal VA from
the level detection unit 16 are input to the selection unit 200.
[0054]
Here, if VH / VA is smaller than a predetermined value (that is, the proportion of high frequency
component signals is small), it is considered that the proportion of occurrence of a correction
error generated to correct high frequency component signals is small. The selection means 200
connects the output side of the Rch and middle-low range correction means 12 by the switch 21
and the selection means 201 connects the output side of the Lch and the middle-low range
correction means 14 by the switch 22.
[0055]
If VH / VA is larger than a predetermined value (that is, the proportion of high frequency
component signals is large), it is considered that the proportion of occurrence of correction error
generated to correct the high frequency component signals is large. The switch 21 connects the
output side of the Rch and the high band correction means 13, and the selection means 201
connects the output side of the Lch and the high band correction means 14 by the switch 22.
[0056]
As described above, the result of comparing the ratio (ratio) of the level of high frequency
component (envelope of high frequency component) VH in the FM stereo demodulated signal to
the level of full band (envelope of full band) VA and a predetermined value Since the correction
means is selected according to the correction error can be reduced.
[0057]
Also, these processes described above may be executed by digital signal processing using a DSP
(Digital Signal Processor) or the like after A / D conversion (Analog to Digital conversion) of the
output signal of the FM detection circuit 1.
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In this case, the correction means which is not selected among the middle and low band
correction means 12 and 14 and the high band correction means 13 and 15 can omit the process
for correction.
[0058]
In addition, although the HPF 25 shown in FIG. 3 is used as the high band level detection means
17 or 19, the component of 15 kHz or more is basically unnecessary, for example, of the stereo
demodulated signal. You may use BPF which can be removed.
[0059]
In addition, although the case of using linear interpolation as the correction method has been
described, the signal in the noise period is subjected to linear interpolation and is further passed
through the LPF to suppress high frequency components of the correction error and then
replaced with the signal (noise) in the noise period. Also good.
[0060]
In the above description, when the signal level of VH is large (in this case, the signal level of VA
also increases), the value of VH (level output of high band level detection means) with respect to
VA (level output of level detection means) Although the operation of the selection means is
determined based on the relation between the ratio (VH / VA) and the predetermined value, for
example, when the signal level of VH does not become extremely large, the selection means is
based on the relation between only VH and the predetermined value. It is needless to say that it
may decide the action of.
[0061]
(Regarding High-Frequency Correction Means Using LPF) An example of the configuration of the
high-frequency correction means 13 and 15 will be described with reference to the signal
waveforms shown in FIG.
The high frequency band correction means 13 and 15 are configured to include an LPF (low pass
filter) on the input side of the input stereo signal.
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[0062]
FIG. 4A shows a state in which pulse noise is included in the input signal input from the stereo
demodulation means 5 in the high band correction means 13 and 15. (The period of the pulse
noise is detected by the noise detection means 110. Will be
Further, in FIG. 4B, the stereo signal shown in FIG. 4A is input to the LPF, and as a result, the
output signal of the LPF in which the high frequency component of the stereo signal is
attenuated (second high frequency correction means Output signal obtained by predetermined
processing in
[0063]
As the characteristics of the LPF used here, it is necessary to sufficiently attenuate the signal in
the pass band of the HPF 25 used for the selection means 200 and 201 (for example, attenuate
to about 1/10 in amplitude level).
[0064]
Therefore, for example, when the cutoff frequency of the HPF 25 is 5 KHz, the LPF used here
should have a cutoff frequency of about 500 Hz (in the case of a first order filter).
[0065]
The portion of the stereo signal that includes the pulsating noise generates a great deal of noise
in the auditory sense, so the signal of the portion is corrected as follows.
That is, the portion of the output signal of the LPF (FIG. 4 (b)) in which the high frequency
component of the stereo signal described above is attenuated (FIG. 4 (b)) Signal) as the correction
signal.
[0066]
As a specific example, the output signal having the signal level P is held as timing when the
output signal of the noise detection unit 110 becomes H level (high level in FIG. 4B), and pulse
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noise is included. It is held during the period (pulse noise generation period shown in FIG. 4A).
[0067]
The state of the stereo signal in this case is shown by the solid line in FIG. 4 (c).
If the LPF output signal (FIG. 4 (b)) in which the high frequency component of the stereo signal is
attenuated is not used, but is simply held at the previous value, the correction error is as shown
by the broken line in FIG. 4 (c). It can be large and this can be a loud noise in the ear.
[0068]
That is, by using the output signal of the LPF in which the high frequency component of the
stereo signal described above is attenuated as the correction signal, the state as shown by the
solid line in FIG. 4C can be stably realized, and generation of auditory noise is realized. It can be
suppressed.
[0069]
The output signal of the noise detection unit 110 shown in FIG. 4B is illustrated for the case
where the delay time (t3-t1) generated in the LPF is included, and when adopting a simple
configuration Even if some delay time is included, when the auditory noise is not bothered, the
above-mentioned effect can be obtained without any particular problem.
[0070]
To exactly compensate for the delay time mentioned above, for example, a stereo signal is once
stored in a memory, and the delay time (t3-t1) of the output signal of the noise detection means
110 for this stored stereo signal, on the time axis It can be realized by proceeding with.
[0071]
Further, although the delay time of the LPF here varies depending on the frequency of the stereo
signal, it may be configured to adaptively switch according to the frequency characteristic of the
LPF, for example.
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Furthermore, here, the stereo signal (audio signal) prior to the noise generation point is subjected
to predetermined processing (the LPF output is obtained and the hold value is taken as a
correction signal). The signal may be subjected to predetermined processing (the LPF output is
obtained and the hold value is taken as a correction signal).
Also, predetermined processing is performed on stereo signals before and after noise generation
time (the LPF output is obtained, and hold values before and after noise generation time are
obtained, for example, the average value of those two hold values is corrected Signal) may be
applied.
That is, what processed predetermined processing to at least any one stereo signal before or after
the noise generation time may be used as a correction signal.
[0072]
Second Embodiment
FIG. 5 is a block diagram of a noise removal apparatus according to a second embodiment of the
present invention.
In the figure, 5 is a stereo demodulation means, 12 is a medium / low band correction means for
correcting the middle low band signal of Rch of stereo demodulation means 5, 13 is a high band
signal of Rch of stereo demodulation means 5. It is a high frequency correction means for
performing interpolation.
[0073]
21 is a switch for switching the output signals of the high band correction means 13 and the
middle low band correction means 12, 14 is a middle low band correction means for the Lch
middle low band signal of the stereo demodulation means 5, and 15 is a stereo demodulation
means 5 is a high frequency correction means for the high frequency signal of Lch of 5;
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The high band correction means 13 and 15 adopt the same configuration as that described in the
first embodiment, including an LPF on the input side of the stereo signal.
[0074]
22 is a switch for switching the output signals of the high band correction means 15 and the
middle low band correction means 14, 16 is a level detection means of the output signal of the
switch 21, and 17 is a high band for detecting high band components of the output signal of the
switch 21. It is a level detection means.
[0075]
Reference numeral 18 denotes level detection means for detecting the level of the output signal
of the switch 22, and reference numeral 19 denotes high band level detection means for
detecting the high band component of the output signal of the switch 22.
[0076]
28 is selection means for controlling the switches 21 and 22 in accordance with the level
detection means 15 and 17 and the output levels of the high band levels 16 and 18, 111 is in
accordance with the outputs from the high band level detection means 17 and 19 It is noise
detection means for adjusting the sensitivity of noise detection.
[0077]
Next, portions different from the first embodiment in operation will be described.
FIG. 6 shows the case where small pulse noise is corrected (here, noise having an amplitude of up
to 50% of the amplitude level of the signal waveform is referred to as small pulse noise).
[0078]
In FIG. 6, (a) shows an example of the waveform before the small pulse noise is corrected, and (b)
shows an example of the waveform after the correction.
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As can be seen by comparing FIGS. 6 (a) and 6 (b), in the example shown, the level difference
(error) becomes larger in the waveform after correction than in the waveform before correction
(the original signal The waveform is largely deformed from the waveform.
In the example shown in FIG. 6, due to the fact that the waveform is largely deformed with
respect to the portion corrected from the original sine wave, the noise may be increased as a
result of the correction.
In particular, when correcting a high frequency signal, this tendency is large because the
correction error becomes large.
[0079]
Therefore, when the high frequency component is large, the detection sensitivity of the pulsative
noise is lowered, and the small noise is not detected, and the correction by the correction means
12 to 15 is not performed.
[0080]
FIG. 7 shows an example of the detection means 111 capable of realizing the above-described
operation.
The operations of the HPF 6, the noise amplifier 7, the waveform shaping circuit 9, and the
integrating circuit 10 shown in FIG. 7 are the same as those in the conventional device.
Further, the adder 28 weights the output of the integrating circuit 10 and the outputs of the high
band level detecting means 17 and 19 via the weighting unit 29 and the weighting unit 30
(multiplies coefficients respectively.
Of course, the outputs after adding the coefficient to 1) are added, and the addition result is input
to the noise amplifier 7 as a control signal.
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[0081]
Here, the noise amplifier 7 reduces the gain as the control signal (addition result) described
above increases.
Therefore, the gain of the noise amplifier 7 when the outputs of the high band level detection
means 17 and 19 are 0 works to keep the average level of the output signal of the noise
detection circuit 8 constant.
[0082]
The average level of the output signal of the noise detection circuit 8 is smaller than the
threshold of the waveform shaping circuit 9.
However, the gain of the noise amplifier 7 does not change with respect to a signal that changes
rapidly with time, so when pulsating noise is added to the noise amplifier 7, the output of the
noise detection circuit 8 becomes larger than the threshold of the waveform shaping circuit 9.
The waveform shaping circuit 9 outputs an H level to detect pulse noise.
[0083]
Here, even if pulse noise having a size equal to or less than the difference between the average
value of the output of the noise detection circuit 8 and the threshold value of the waveform
shaping circuit 9 is generated, it is not detected.
Therefore, when detecting even small pulse noise, the difference between the average value of
the output signal of the noise detection circuit 8 and the threshold value of the waveform
shaping circuit 9 is reduced, and when the small pulse noise is not detected, the noise detection
circuit 8 The difference between the average value of the output signal of the above and the
threshold value of the waveform shaping circuit 9 may be increased.
[0084]
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20
Next, when the high frequency level signal is included in the stereo demodulation signal and the
output of high frequency level detection means 17 and 19 becomes large, the control signal of
the noise amplifier becomes large. The gain is smaller.
[0085]
For this reason, the average value of the output signal of the noise detection circuit 8 becomes
small, and the difference with the threshold value of the waveform shaping circuit 9 becomes
large, so that small pulse noise can not be detected.
[0086]
As described above, if the level of the high frequency component of the stereo FM-demodulated
signal is large, the detection sensitivity of the pulse noise is reduced (that is, the detection
sensitivity is variable according to the output level of the high frequency level detection means).
The correction error due to the correction of the small pulse noise is reduced.
[0087]
In addition, these processes described above may perform A / D conversion of the output signal
of the FM detection circuit 1 and execute the subsequent process using a digital signal
processing technique by a DSP or the like.
In this case, it is possible to omit the process for correction in the correction means which is not
selected among the middle and low band correction means 12 and 14 and the high band
correction means 13 and 15.
[0088]
Third Embodiment
8 is a block diagram of a noise eliminator according to a third embodiment of the present
invention.
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In the figure, reference numeral 112 denotes noise detection means for detecting pulse noise
from the output of the FM detection circuit 1, and reference numeral 120 denotes correction of
the middle to low frequency signal when there are many middle to low frequency components of
the output signal of the FM detection circuit 1. Medium / low band correction means for
applying, 130 is a high band correction means for correcting the high band signal when there are
many high band components of the output signal of the FM detection circuit 1, 21 is a middle /
low band These switches are switches for switching the outputs of the correction means 120 and
the high frequency correction means 130.
The high frequency band correction unit 130 employs the same configuration as that described
in the first embodiment, including an LPF on the input side of the stereo signal.
[0089]
Reference numeral 5 denotes stereo demodulation means connected to the output signal of the
switch 21; 160, level detection means for detecting the level of the Lch signal of the stereo
demodulation means 5; 170, the high band signal level of the Lch signals of the stereo
demodulation means 5 Reference numeral 180 denotes a level detection means for detecting the
signal level of the Rch signal of the stereo demodulation means 5.
[0090]
190 is a high band level detection means for detecting the high band signal level of the Rch
signal of the stereo demodulation means 5, 300 is a size of L-R component which is a difference
between the signal level of Lch signal and the signal level of Rch signal (Subtracted signal level.
Note that L-R level detection means for detecting R-L component), 301 indicates the magnitude
of L + R component (the level of the addition signal) which is the sum of the signal level of Lch
signal and the signal level of Rch signal Means for detecting L + R levels.
[0091]
Reference numeral 400 denotes selection means for switching the switch 21 in accordance with
the outputs of the level detection means 160, 180, the high frequency detection means 170, 190,
and the L-R level detection means 300.
08-05-2019
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[0092]
Next, the operation will be described.
First, the noise detection means 112 detects pulse noise in the same manner as the detection
means 11 in the conventional device, for example.
The output signal of the noise detection means 112 outputs high level (H level) gate signal
during a period when pulse noise is detected, and low level (L level) gate signal during a period
when the pulse noise is not detected. And the low to high frequency correction means 120.
[0093]
Next, the correction means 120, 130 corrects the signal in which the gate signal is in the H level
period.
Here, the output signal of the FM detection circuit 1 to be corrected is composed of an L + R
component of 0 to 15 kHz, an L-R component AM-modulated at 38 kHz in a band of 23 to 53
kHz, and a pilot signal of 19 kHz.
[0094]
Therefore, when correction corresponding to pulse noise of several tens of μs width is
performed on a signal containing a large amount of L-R component, pulse noise of several
wavelengths may be present within the correction period, and the previous value is simply held.
When linear interpolation or the like is performed, the correction error may be rather large.
In this case, the high-frequency correction means 130 is used to reduce the error due to the
correction.
[0095]
08-05-2019
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Further, when the output signal of the FM detection circuit 1 has a small L-R component, the
component of 23 k to 53 kHz is small, so that the high frequency component of the L + R
component is small. Since this is equivalent to the fact that the high frequency component is
small, it is possible to make the correction error small by simply holding the previous value or
performing linear interpolation.
[0096]
Therefore, in this case, the selection means 400 operates to connect the switch 21 to the middlelow range correction means 120 when the conditions shown in the following (1) and (2) are
satisfied.
(1) The output of the L-R level detection means 300 is sufficiently smaller than the output signal
of the L + R level detection means 301.
(2) The output of the high band level detection means 170 and 190 is sufficiently smaller than
the output of the level detection means 160 and 180.
[0097]
Here, the output signal of the L-R level detection means 300 is obtained, for example, from the
output of inputting the absolute value of the difference between the stereo-demodulated Lch
signal and the Rch signal to the LPF.
Further, the output signal of the L + R level detection means 301 can be obtained, for example,
from the output of the LPF to which the absolute value of the sum of the Lch signal FMdemodulated to stereo and the Rch signal is input.
[0098]
As described above, when the above conditions (1) and (2) are satisfied, the output signal from
the FM detection circuit 1 has few high frequency signal components, so correction is simply
performed by linear interpolation or the like. If this is done, the error from the original
demodulation signal can be reduced.
08-05-2019
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[0099]
In addition, these processes described above may perform A / D conversion of the output signal
of the FM detection circuit 1 and execute the subsequent process using a digital signal
processing technique by a DSP or the like.
[0100]
Further, in the description of the above-described embodiment, although the signal after the FM
demodulation of stereo is processed and input to the selection means 400, the high frequency
signal in the composite signal in which the output signal of the switch 21 is corrected. The level
is detected, and when this is small, the L-R component is small, and the high frequency
component of the signal FM-demodulated to stereo is also small, so that the switch 21 is
connected to the middle low frequency correction means 120 It is good.
[0101]
As described above, according to the present invention, the following effects can be obtained.
[0102]
The noise removal device according to the present invention comprises noise detection means for
detecting noise contained in an FM demodulation signal, audio signal demodulation means for
demodulating an audio signal contained in the FM demodulation signal, and output from the
audio signal demodulation means A first correction unit that receives the audio signal as an input
and outputs a correction signal of the audio signal based on the audio signal before and after the
noise generation point detected by the noise detection unit; and the audio signal demodulation
unit The audio signal is corrected based on a signal obtained by applying predetermined
processing to the audio signal at least any one before or after the generation point of noise
detected by the noise detection unit, using the audio signal to be output as an input A second
correction means for outputting a signal, and the above-mentioned audio output from the audio
signal demodulation means A high band level detection means for detecting the level of the high
band component of the Dio signal, and a selection means for selecting either the first or second
correction means based on the output of the high band level detection means. Therefore, even if
the audio signal contains high frequency components, the high frequency components are
detected, and when the ratio of high frequency components is large, the correction with less
error is selected for the high frequency signal. By this, it is possible to reduce the correction error
when the proportion of high frequency components is large.
08-05-2019
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[0103]
Further, the first correction means is characterized in that it outputs low-pass filter output of a
signal value obtained from linear interpolation of two signal values present immediately before
and after the noise generation time point as a correction signal, so that it is low. A correction
error can be reduced when the ratio of frequency components is large.
[0104]
Further, the signal value obtained by holding the low-pass filter output of the audio signal output
from the audio signal demodulation means just before the point of occurrence of noise in the
audio signal is set as a correction signal by predetermined processing in the second correction
means. As a result, the amount of processing required to obtain a correction signal can be
reduced.
[0105]
Further, the second correction means can be obtained from linear interpolation of two average
signal values obtained by averaging a plurality of signal values respectively existing before and
after the noise generation time point corresponding to the noise generation time. Since the low
pass filter output of the signal value is used as the correction signal, it is possible to accurately
perform the signal correction when the ratio of the high frequency component is large, and it is
possible to reduce the correction error.
[0106]
The signal processing apparatus further comprises level detection means for detecting the level
of the entire band in the demodulated audio signal, and selection is made based on the ratio of
the level output of the high band level detection means to the level output of the level detection
means and a predetermined value. Since the means is operated, noise can be reliably captured
even when the output from the high frequency level detection means becomes large.
[0107]
Further, since the noise detection means is characterized in that the detection sensitivity is
variable according to the output level of the high band level detection means, the generation of a
large error due to the correction when noise at a low level is included It can prevent.
[0108]
Further, the FM demodulation signal is input to the first correction means and the second
correction means, and selection is made based on the level of the addition signal and the level of
08-05-2019
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the subtraction signal between the right channel signal and the left channel signal constituting
the audio signal. As it is characterized in that it operates the means, it is possible to make
corrections which are adapted to the received signal.
[0109]
Since the audio apparatus according to the present invention is characterized by including the
noise removal apparatus described in any of the above, even if the noise is included, the noise is
appropriately corrected with respect to the noise to obtain the quality. An audio output device
capable of obtaining high audio output can be realized.
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