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JP2002345075

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DESCRIPTION JP2002345075
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
signal processing apparatus such as an equalizer apparatus for adjusting the frequency
characteristic of an audio signal, which can appropriately change the level on the frequency axis.
[0002]
2. Description of the Related Art A signal processing apparatus for obtaining various desired
viewing environments by changing various characteristics such as frequency characteristics,
phase characteristics and sound field characteristics of digitized audio signals using a DSP
(Digital Signal Processor) or the like. Are variously developed. As an example of this type of
signal processing device, in the graphic equalizer device, a plurality of level adjustment units for
changing the level for each predetermined frequency band are provided in parallel, and the user
operates the display operation unit of the level adjustment unit. By operating while visually
confirming the frequency characteristic can be arbitrarily adjusted.
[0003]
An example of level adjustment processing in a conventional graphic equalizer device will be
described. FIG. 8 is an explanatory view showing level change of each frequency band. When
changing the level of the digital signal, raising the level may cause the signal to clip beyond the
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maximum level of the digital signal system (for example, the maximum value of full bit = 0 dB).
For this reason, in the graphic equalizer device that digitally changes the level, when raising the
level in the digital signal system, the level adjustment is performed to lower the level of the input
signal over the entire frequency band, and the original lowered in the digital signal system. A
configuration is adopted in which the analog signal system is amplified to the level. This makes it
possible to prevent unnatural level changes at the input and output of the graphic equalizer
device.
[0004]
For example, when changing the level for each frequency band as shown in FIG. 8, the level
change characteristics 101a, 101b, and 101c of each band are determined by the set variable
value and the frequency characteristic for each band. The level change characteristic 102 of the
entire frequency band combining these level change characteristics 101a to 101c has the
maximum level change amount larger than the level change amount of each band, but the
maximum value of the level change amount can be determined. It was not. For this reason, the
level of the input signal is uniformly lowered when performing level adjustment so that the signal
does not clip, in consideration of the margin for the maximum variable level change
characteristic. For example, in a graphic equalizer device that is variable by ± 8 dB in each band,
the level adjustment unit uniformly reduces 12 dB in consideration of the above-mentioned
margin.
[0005]
In the signal processing apparatus as described above, when the level is lowered in the digital
signal system and then amplified in the analog signal system in the subsequent stage, the noise
components after the D / A converter are also amplified together. Therefore, the S / N is
degraded by the gain of this level reduction / amplification. Therefore, as in the conventional
device described above, if the level is not raised too much in the level adjustment unit if the level
is uniformly lowered in advance in consideration of the margin in the digital signal system, S
more than necessary. There is a problem that / N gets worse.
[0006]
The present invention has been made in view of the above circumstances, and it is possible to
lower the level by the maximum increase according to the level change characteristic on the
frequency axis in the digital signal system so that the signal does not clip when the characteristic
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is changed. An object of the present invention is to provide a signal processing device capable of
suppressing the deterioration of N.
[0007]
A first aspect of the present invention is a signal processing apparatus having a signal
characteristic variable circuit for changing the characteristic of a digital audio signal, the level in
the frequency space of the signal characteristic variable circuit. A maximum value acquisition
means for obtaining the maximum value of the change characteristic, and a level correction
means for reducing the level of the digital signal in accordance with the maximum value in the
signal characteristic variable circuit.
[0008]
Also preferably, secondly, the level correction means decreases the level of the digital signal by
the maximum value in the signal characteristic variable circuit.
[0009]
In the above configuration, the maximum value of the level change characteristic in the
frequency space in the signal characteristic variable circuit is obtained by operation or the like,
and the level of the digital signal is reduced by the maximum value according to the maximum
value in the signal characteristic variable circuit. Do.
As a result, in order to prevent the signal from clipping when changing the characteristic, the
level correction is performed with only the minimum level reduction in accordance with the level
change characteristic of the signal characteristic changing circuit.
Therefore, the dynamic range in the digital signal system is secured to the maximum, and the
deterioration of S / N is suppressed.
[0010]
Preferably, thirdly, a D / A conversion circuit for converting a digital signal processed in the
signal characteristic variable circuit into an analog signal, and an amplifier circuit for amplifying
a level decrease in the level correction means in the analog signal Equipped with
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[0011]
In the above configuration, the level correction of the digital signal is performed and the signal
characteristic is changed, and the digital signal is converted into an analog signal to amplify the
level decrease.
As a result, the signal subjected to the level correction is returned to the original level, so that a
natural level correction without a sense of discomfort for the user is made.
At this time, since the amplification of the analog signal can be minimized, the deterioration of
the S / N can be suppressed.
[0012]
Still preferably, fourthly, the maximum value acquisition means generates impulse signals and
obtains impulse response characteristics of the signal characteristic variable circuit, and
coordinate conversion for converting the impulse response characteristics into a frequency
space. Means, and maximum value calculation means for calculating the maximum value of the
frequency characteristic of the impulse response.
[0013]
In the above configuration, the impulse response characteristic of the signal characteristic
variable circuit is obtained, converted into a frequency space by Fourier transform or the like,
and the maximum value of the frequency characteristic of the impulse response is searched and
calculated.
Thus, the maximum value of the level change characteristic in the frequency space in the signal
characteristic variable circuit can be accurately obtained according to the characteristic of the
current setting state.
[0014]
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Preferably, fifthly, the signal characteristic variable circuit is an equalizer that changes the level
of a predetermined frequency band in a digital audio signal. Alternatively, sixthly, the signal
characteristic variable circuit includes at least one of a filter for passing a predetermined
frequency band in a digital audio signal, a delay for changing a delay amount, and a level
converter for changing a level. It shall be a processor.
[0015]
By applying the configuration of the present invention to a signal processing apparatus having an
equalizer, an audio processor or the like as the signal characteristic variable circuit as described
above, the deterioration of S / N in these signal processing apparatuses is suitably suppressed.
[0016]
The seventh aspect of the present invention is signal characteristic variable means for changing
the characteristic of a digital audio signal, maximum value acquisition means for obtaining the
maximum value of the level change characteristic in the frequency space in the signal
characteristic variable means, and the signal characteristic. And a program for causing a
computer to function as signal processing means including level correction means for decreasing
the level of the digital signal in accordance with the maximum value in the variable means.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be
described below with reference to the drawings.
FIG. 1 is a block diagram showing the configuration of an audio apparatus provided with a signal
processing apparatus according to an embodiment of the present invention.
This audio device is generally called an AV amplifier and has functions such as input selection of
various audio signals, adjustment processing of frequency characteristics and sound field
characteristics, and signal amplification.
[0018]
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The signal input unit has an input interface for digital audio signals, a digital input unit 11 for
selecting and decoding the input of digital signals, and an input interface for analog audio signals
and converts an analog signal to a digital signal A / And a D converter (ADC) 12. The digital input
unit 11 is configured by a digital audio interface receiver (DIR) or the like.
[0019]
A signal processing unit 13 comprising a DSP (Digital Signal Processor) or the like constituting a
signal characteristic variable circuit is provided at a stage subsequent to the digital input unit 11
and the A / D converter 12, and various signal processing is performed on digital signals here. It
is supposed to be. At the subsequent stage of the signal processing unit 13, a D / A converter
(DAC) 14 as a D / A conversion circuit for converting a digital signal into an analog signal, an
amplifier 15 as an amplification circuit for amplifying an analog signal, and adjusting the signal
output level A volume 16 is provided to output an analog audio signal to a speaker or the like.
The volume 16 is composed of an electronic volume or a resistor array and a changeover switch.
[0020]
Further, a display unit 17 including a display panel of a fluorescent display tube for displaying an
operation state of the apparatus and the like, and an equalizer operation unit 18 including a slide
switch and a touch panel for adjusting the graphic equalizer are provided. . A control unit 19
such as a microcomputer (MPU) or the like is provided and connected to each unit of the
apparatus to perform operation control.
[0021]
FIG. 2 is a block diagram showing a configuration example of a signal processing unit according
to the first embodiment. In the first embodiment, a digital level correction unit 21 and a graphic
equalizer (GEQ) 22 are configured in the signal processing unit 13, and the digital equalizer is
operated by raising and lowering the level for each of a plurality of frequency bands by the
graphic equalizer 22. The case of adjusting the frequency characteristic in the example is
illustrated. In this case, the input digital signal is adjusted in frequency characteristic of the entire
band by the graphic equalizer 22, converted into an analog signal by the D / A converter 14,
amplified by the amplifier 15, and output. Note that the digital level correction unit 21 and the
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graphic equalizer 22 configured in the signal processing unit 13 are not limited to the order of
the digital level correction unit 21 → the graphic equalizer 22 by using, for example, a floating
point type DSP. It can also be configured in the order of the digital level correction unit 21.
[0022]
When varying the signal level with the graphic equalizer 22, the maximum value of the level
increase in the combined level change characteristic in all frequency bands is determined by
calculation so as not to exceed the maximum level (full bit value) of the digital signal system. The
digital level correction unit 21 of the input stage of the graphic equalizer 22 performs correction
so as to lower the level by the maximum value. At this time, the signal processing unit 13 and the
control unit 19 constitute a maximum value acquisition unit, and the digital level correction unit
21 constitutes a level correction unit.
[0023]
Then, the level correction component is amplified in the analog signal system amplifier 15 in the
latter stage to restore the original signal level. As a result, it is possible to eliminate unnatural
level changes at the input and output of the graphic equalizer, and to make the user feel
comfortable when listening to it. Such level increase correction processing in the graphic
equalizer will be described below with reference to FIGS.
[0024]
FIG. 3 is a characteristic diagram showing an example of adjustment of frequency characteristics
by the graphic equalizer. Here, as shown in FIG. 3, a case is considered where +4 dB is boosted
(the level is raised) at 8 kHz and 16 kHz. In this case, a synthetic level change characteristic 33 in
which the level change characteristics 31 and 32 of the respective bands are synthesized is
obtained by calculation to obtain the maximum value A. The composite level change
characteristic 33 is obtained by performing an operation using the impulse response
characteristic of the graphic equalizer by the configuration of the maximum value acquiring
means as shown in FIG.
[0025]
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FIG. 4 is a block diagram showing a functional configuration when calculating composite level
change characteristics in the graphic equalizer. As a method of calculating the composite level
change characteristic 33, first, the impulse response δ (n) is input to the graphic equalizer 41
whose level adjustment has been set by the impulse response acquisition means, and the impulse
response h of the graphic equalizer 41 obtained as its output n) is Fourier-transformed by an FFT
unit (fast Fourier transform unit) 42 which is coordinate conversion means to obtain a frequency
component g (ω). Then, the maximum value search unit 43, which is a maximum value
calculation unit, searches for the maximum value A in all frequency bands from the frequency
component g (ω) of the impulse response. This maximum value A is the maximum value of the
level increase in the current setting of the graphic equalizer 41. By the above method, the
maximum value of the synthetic level change characteristic in the graphic equalizer can be
accurately obtained. The impulse response acquisition unit, the coordinate conversion unit, and
the maximum value calculation unit are configured in the control unit 19 and the signal
processing unit 13.
[0026]
FIG. 5 is a flowchart showing the procedure of calculating the correction value of the level
increase by the graphic equalizer. When the user uses the graphic equalizer, the user operates
the equalizer operation unit 18 while watching the display on the display unit 17 to adjust the
level of each band. First, in step S1, it is determined whether the setting of the graphic equalizer
has been changed by the user operating the equalizer operation unit 18 or the like, and the
setting is changed and the frequency characteristic of the output level of the graphic equalizer
itself changes. The process proceeds to step S2 to enter a level correction value setting mode.
[0027]
Then, in step S3, the impulse signal δ (n) is input to the graphic equalizer 41. In step S4, the
impulse response of the graphic equalizer 41 is Fourier-transformed by the FFT 42 to obtain the
frequency component g (ω). Next, in step S5, the maximum value A is retrieved from the
frequency component g (ω) of the impulse response. Thereafter, in step S6, the value of the
maximum value A is set as the level increase correction value d, and the process proceeds to the
normal mode in step S7. By storing the level increase correction value d obtained as described
above in a memory or the like, it is possible to perform appropriate digital level correction in the
front stage of the graphic equalizer.
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[0028]
The above-described calculation of impulse response, FFT, maximum value search and the like
are performed in the signal processing unit 13 according to the instruction of the control unit 19
in FIG. That is, in an actual graphic equalizer configured by the DSP of the signal processing unit
13, the impulse response is obtained to calculate the maximum value A of the composite level
change characteristics in all frequency bands.
[0029]
FIG. 6 is an operation explanatory diagram showing level change in the input / output stage of
the graphic equalizer. FIG. 6 shows level changes at 1 kHz (without level change) and 11 kHz
(maximum level change) in the frequency characteristics of the graphic equalizer shown in FIG. A
solid line X1 and a broken line Y1 are operation examples of this embodiment, and X1 indicates
11 kHz and Y1 indicates 1 kHz. Further, an alternate long and short dash line X2 and an
alternate long and two short dashes line Y2 are operation examples of the conventional example,
where X2 indicates 11 kHz and Y2 indicates 1 kHz. Here, it is assumed that a 0 dB digital signal
is input to the signal processing unit 13.
[0030]
In the present embodiment, the digital level correction unit 21 at the input stage of the signal
processing unit 13 reduces the level as the level increase correction value d of the maximum
value A of the composite level change characteristic obtained as described above in the previous
stage of the graphic equalizer 22. Do. When the graphic equalizer 22 performs level adjustment
for each frequency band, the level is increased by the maximum value A at 11 kHz. Then, in the
state of the analog signal after conversion in the D / A converter 14, the gain of the level
decrease A due to the level increase correction value d is amplified by the amplifier 15 in the
subsequent stage so that the level becomes 0 dB at 1 kHz. Make it In this case, amplification of
noise components in the analog signal system can be minimized, and a large dynamic range D1
of the output signal can be secured.
[0031]
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On the other hand, even when the level B is reduced as the level increase correction value d in
the preceding stage of the graphic equalizer as the level increase correction value d, the level is
increased by 11 kHz at the maximum level A. Then, in order to return to the original signal level
after conversion by the D / A converter 14, it is necessary to amplify the gain of the level
decrease B by the amplifier 15 at the subsequent stage. In this case, the amplification gain of the
noise component also increases together, so the dynamic range D2 decreases by the gain
increase in the analog signal system, that is, by the margin α.
[0032]
As the amplifier 15 for amplifying the analog signal, an amplifier capable of varying the gain in
fine steps in accordance with the control signal from the control unit 19 is used. As a result, it is
possible to perform amplification by an amount corresponding to the level decrease in the digital
level correction unit 21 at the previous stage, that is, the maximum value A of the composite level
change characteristic of the graphic equalizer 22.
[0033]
As described above, in the present embodiment, it is possible to obtain the maximum value of the
level increase in all frequency bands at the current level setting of the graphic equalizer by the
calculation using the impulse response characteristic of the graphic equalizer. By reducing the
level of the maximum value in the previous stage by the maximum level, it is possible to minimize
the S / N deterioration while preventing the input signal from clipping beyond the maximum
level in the digital signal system. It is.
[0034]
FIG. 7 is a block diagram showing a configuration example of a signal processing unit according
to the second embodiment.
In the second embodiment, in place of the graphic equalizer of the first embodiment, a filter 51
of variable cutoff frequency type, a delay 52 of variable delay amount type, and a level converter
(amplifier) 53 of variable gain type in the signal processing unit 13. An example is shown in
which an adder 54 is provided to configure an audio processor that mixes the signal whose
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characteristic has been changed with the original signal. This configuration is used in a sound
field processor, an effector or the like that performs signal processing to change a frequency
characteristic or a reverberation characteristic or add a reflected sound to form a desired sound
field.
[0035]
In this case, the input digital signal is band-limited by filter 51 to pass only a predetermined
frequency component, delayed by a predetermined amount on a time axis by delay 52, and a
predetermined amount of level by level converter 53. An increase or decrease is made. Then, the
original signal and the signal whose characteristic has been changed by the adder 54 are added
and mixed. When the signal characteristics are changed by such a filter, delay, and level
converter, the output signal has a predetermined frequency on the frequency axis, even when the
input signal has a flat characteristic as shown in FIG. The level changes in the band.
[0036]
In such audio processors, conventionally, it has been difficult to obtain composite level change
characteristics in the frequency band and to obtain the maximum value for the level increase, but
by using the above-described operation based on the impulse response characteristic, the first As
in the embodiment, the maximum value of the combined level change characteristic can be
accurately determined. Therefore, the amplification gain in the analog signal system at the
subsequent stage can be minimized by reducing the level at the former stage of the audio
processor as the level increase correction value by the maximum value calculated similarly to the
first embodiment. It is possible to secure a larger dynamic range of the output signal while
preventing saturation of the signal level in the digital signal system.
[0037]
In the embodiment described above, when the characteristic of the signal processing unit such as
the graphic equalizer is changed by the operation of the user or the like in the maximum value
acquiring unit, the maximum value of the composite level change characteristic in the frequency
band is determined to increase the level Although the correction value is set, the present
invention is not limited to this. For example, the maximum value of the combined level change
characteristic is determined in advance for each characteristic setting to determine the level
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increase correction value, and stored in a memory or the like using a correction table or the like.
The corresponding level increase correction value may be read out. However, according to the
configuration of the above embodiment, the memory for storing the level increase correction
value can be minimized, and can be realized only by program change or addition of the DSP or
MPU. It can be suppressed and is more preferable.
[0038]
In the above-described embodiment, when obtaining the maximum value of the combined level
change characteristic in the frequency band of the signal processing unit, the DSP of the signal
processing unit performs the operation according to an instruction from the MPU or the like of
the control unit. If there is no problem in the calculation capability or the like, the MPU may
perform the calculation to set the maximum value.
[0039]
Further, in the embodiment described above, when performing level adjustment according to the
determined maximum value, an example is shown in which the maximum value itself is the level
reduction amount as a typical example, but the present invention is not limited to this. The level
may be lowered by adding a predetermined value including a margin to the maximum value.
[0040]
In addition, the functions of each means can be realized by a program that executes the
technology of the above-described embodiment in a computer such as a personal computer (PC),
and this program is online via a recording medium such as a CD or a network. Distribution is
possible.
[0041]
As described above, when performing level correction in the digital signal system in order to
prevent signal clipping due to a change in the frequency characteristic etc. by the signal
processing unit, the maximum value of the synthetic level change characteristic of the actual
signal processing unit is determined By reducing the level according to the maximum value, it is
possible to minimize the level reduction in the digital signal system and to make the dynamic
range as large as possible.
As a result, since the amplification gain for level adjustment in the analog signal system in the
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subsequent stage can be minimized, the deterioration of S / N can be suppressed.
[0042]
As described above, according to the present invention, it is possible to execute level correction
only with the minimum level reduction according to the level change characteristic of the signal
characteristic variable circuit so that the signal is not clipped when the characteristic is variable.
The dynamic range of the digital signal system can be maximized, and the deterioration of S / N
can be suppressed.
[0043]
In addition, since the level correction of the digital signal is performed, the signal characteristic is
changed, and the digital signal is converted into an analog signal to amplify the level decrease, so
that the signal subjected to the level correction is returned to the original level. A natural level
correction without a sense of incongruity for the user is possible, and at this time amplification of
the analog signal can be minimized, so that the deterioration of S / N can be suppressed.
[0044]
In addition, the impulse response characteristic of the signal characteristic variable circuit is
obtained, converted to a frequency space by Fourier transform or the like, and the maximum
value of the frequency characteristic of the impulse response is searched and calculated to obtain
the frequency characteristic of the signal characteristic variable circuit. The maximum value of
the level change characteristic of can be accurately obtained according to the characteristic of
the current setting state.
[0045]
The circuit also includes at least one of an equalizer that changes a level of a predetermined
frequency band, a filter that passes a predetermined frequency band, a delay that changes a
delay amount, and a level converter that changes a level as a signal characteristic variable circuit.
By applying to a signal processing apparatus having an audio processor or the like, deterioration
of S / N in these signal processing apparatuses can be suitably suppressed.
[0046]
Brief description of the drawings
[0047]
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1 is a block diagram showing the configuration of an audio apparatus provided with a signal
processing apparatus according to an embodiment of the present invention.
[0048]
2 is a block diagram showing a configuration example of a signal processing unit according to
the first embodiment.
[0049]
3 is a characteristic diagram showing an example of adjustment of the frequency characteristic
by the graphic equalizer.
[0050]
4 is a block diagram showing a functional configuration when calculating composite level change
characteristics in the graphic equalizer.
[0051]
5 is a flowchart showing a calculation procedure of the correction value of the level increase by
the graphic equalizer.
[0052]
6 is an operation explanatory diagram showing the level change in the input and output stage of
the graphic equalizer.
[0053]
7 is a block diagram showing a configuration example of a signal processing unit according to
the second embodiment.
[0054]
8 is an explanatory view showing the level change of each frequency band in the conventional
example.
[0055]
Explanation of sign
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[0056]
11 digital input unit 12 A / D converter (ADC) 13 signal processing unit (DSP) 14 D / A converter
(DAC) 15 amplifier 16 volume 17 display unit 18 equalizer operation unit 19 control unit 21
digital level correction unit 22, 41 graphics Equalizer 31, 32 Level change characteristic in each
band 33 Synthetic level change characteristic 42 FFT unit 43 Maximum value search unit 51
Cutoff frequency variable type filter 52 Delay amount variable type delay 53 Gain variable type
level converter
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