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JPH09162663

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DESCRIPTION JPH09162663
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
tone control device for performing tone adjustment of an audio signal by digital signal
processing.
[0002]
2. Description of the Related Art FIG. 8 is a block diagram showing the configuration of a
conventional tone control device. In FIG. 8, the tone control device of this example includes a low
pass filter (LPF) 1, an A / D converter 2, a digital signal processor (DSP) 3, a D / A converter 4,
and an LPF 5. .
[0003]
Next, the operation of this conventional example will be described. In FIG. 8, in this tone control
device, even when the analog audio signal of the full level which is a full bit is inputted from the
LPF 1 to the A / D converter 2, the digital when the tone control is set in the DSP 3 The clip is
blocked, and the levels of the input audio signal and the output audio signal are kept equal
regardless of the input / output level in the frequency band not subjected to gain increase (tone
control) processing. The DSP 3 performs gain increase processing to increase the level of a
specific frequency band to the input audio signal through the LPF 1 and A / D converter 2 and
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attenuates the amount equal to the maximum value of the gain increase amount as a clip margin
/ A converter 4, LPF 5 and DSP 3 increase the amount equal to the amount of gain increase.
[0004]
In the tone control device of the above-described conventional example, when the analog audio
signal of the maximum level which becomes full bit in the A / D converter 2 is input to the A / D
converter 2, The input to DSP3 is full bit. At this time, when the tone control of gain increase is
performed by the DSP 3, a digital clipping state occurs, and noise and abnormal noise are output.
This is because an overflow or aliasing waveform occurs in digital processing in the DSP 3 and
the calculated value is fixed to the maximum value or the minimum value by the overflow
correction processing. Therefore, even if any input audio signal not exceeding the maximum
input level is input, it is necessary to prevent digital clipping when tone control of the gain
increase is performed. In the above conventional example, the input level of the A / D converter 2
decreases by the maximum gain increase of the tone control performed by the DSP 3 and the
performance such as the dynamic range at analog / digital conversion in the A / D converter 2
deteriorates. You In particular, even when level control is not performed in tone control, there
has been a drawback that the performance for the clip margin for preventing digital clipping at
the maximum gain is deteriorated.
[0005]
The present invention solves the problems in the prior art as described above, prevents abnormal
noise generation without providing a clip margin which causes performance deterioration at
analog / digital conversion, and equalizes input / output levels. Provide an excellent tone control
device that can be maintained.
[0006]
SUMMARY OF THE INVENTION In order to achieve the above object, the present invention
attenuates the gain of an input digital audio signal by the input attenuation means of the
preceding stage in response to the gain increase in the tone control means, and controls the tone
control. The gain of the output signal of the means is adjusted by the output gain adjusting
means in the subsequent stage, and the setting amounts of the tone control means, the input
attenuation means and the output gain adjusting means are adjusted according to the gain
variable amount in this tone control means and the change history here. It is controlled by the
control means.
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[0007]
From the above, it is possible to obtain an excellent tone control device capable of preventing
abnormal noise generation and keeping the input and output levels equal.
[0008]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS According to a first aspect of the
present invention, there is provided a tone control means for increasing or decreasing the gain
set in a specific frequency band of an input digital audio signal, and a tone control means
provided in front of the tone control means. Input attenuation means for attenuating the gain of
the input digital audio signal in response to gain increase in the control means; output gain
adjustment means provided downstream of the tone control means for adjusting the gain of the
output signal of the tone control means; It comprises a variable gain amount in the tone control
means and a control means for controlling the set amounts of the tone control means, the input
attenuation means and the output gain adjustment means according to the change history, and
the gain increase amount of the input digital audio signal Attenuate the audio frequency signal to
a digital signal. In this case, the maximum dynamic range in the A / D converter is secured, and
the operation value in the tone control means becomes the maximum value, digital clipping is
prevented, and the input and output levels are kept equal. Have.
[0009]
Further, in the invention according to claim 2, the output gain adjusting means adjusts the gain
of the output signal of the tone control means and has a volume control function.
[0010]
Also, in the invention according to claim 3, the control means sets, in one sampling period, an
amount of gain attenuation equal to the gain increase set by the tone control means in the input
attenuation means, and then, by the tone control means. Setting the gain increase of the output
gain adjustment means equal to the gain increase set by the tone control means in the output
gain adjustment means, and digital clipping does not occur regardless of the order of setting
control It has an effect that abnormal noise does not occur.
[0011]
The invention according to claim 4 is that, when the control means performs control outside one
sampling period, when the gain increase is set by the tone control means, the tone control means
decreases the amount of gain equal to the gain increase. Setting the gain increase in the tone
control means and setting the gain increase amount in the tone control means to decrease after
setting the input attenuation means as the input attenuation means, the gain increase of the same
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amount as the gain increase in the tone control means Is set as the input attenuation means, and
then the gain increase in the tone control means is set. When this control cycle is divided, the
setting of the tone control means is performed after the setting of the input attenuation means,
and digital clipping occurs. It has the effect that no abnormal noise occurs.
[0012]
Next, an embodiment of the tone control device of the present invention will be described in
detail with reference to the drawings.
[0013]
(Embodiment 1) FIG. 1 is a block diagram showing the configuration of an embodiment of a tone
control apparatus according to the present invention.
In FIG. 1, a sound source 11 for outputting a stereo audio signal reproduced by a compact disk
(CD) device or the like, an LPF 12 for passing a predetermined frequency band in the stereo
audio signal from the sound source 11, and a sound source 11 from this LPF 12 And an A / D
converter 13 for converting the audio signal into a digital signal and outputting the digital signal.
Further, the DSP 14 sets and outputs a gain increase set for the audio signal from the A / D
converter 13, and the D / A converter 15 converts the audio signal from the DSP 14 into an
analog signal and outputs the analog signal. And an LPF 16 for removing unnecessary signals of
the audio signal output from the D / A converter 15.
In addition, a tone control adjustment key 17 for setting the user to change the level in a desired
frequency band, an amplifier 18 for amplifying and outputting an audio signal from the DSP 14,
and a stereo audio amplified by the amplifier 18 A speaker 19 for outputting a signal and a
control unit 20 for controlling tone control in the DSP 14 based on the setting of the tone control
adjustment key 17 are included.
[0014]
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The DSP 14 controls an input attenuation unit 14 a that attenuates the audio signal from the A /
D converter 13 by the control of the control unit 20 and an increase in gain by the control of the
control unit 20 with respect to the audio signal attenuated by the input attenuation unit 14 a And
a tone control unit 14b.
The audio signal output from the tone control unit 14b is controlled by the control unit 20 to
perform gain adjustment, and the output gain adjustment unit 14c has a volume control function.
[0015]
Next, the operation of this embodiment will be described.
A predetermined frequency band of the stereo audio signal from the sound source 11 is
extracted through the LPF 12 and converted into a digital signal by the A / D converter 13.
In this case, a stereo audio signal in which the output of the A / D converter 13 is a full bit is
transmitted from the sound source 11.
When the setting of the tone control adjustment key 17 is 0 dB or less, the control unit 20 sets
the input attenuation unit 14 a to be executed by the digital signal processing program in the
DSP 14 to 0 dB, and the tone control unit 14 b is set to the tone control adjustment key 17. Set to
coefficient data based on the setting.
The output gain adjustment unit 14 c is set in the range of normal −∞ or more and 0 dB or less.
The digital audio signal from the DSP 14 is converted into an analog signal, and a predetermined
frequency region is removed through the LPF 16 and output to the amplifier 18, and the audio
signal amplified here is output through the speaker 19. There is no level increase and level
attenuation of the audio signal between the LPF 12 and the LPF 16.
[0016]
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FIG. 2 is a diagram showing an operation state of the DSP 14 when the setting of the tone control
adjustment key 17 is 0 dB or less. In FIG. 2, when the setting of the tone control adjustment key
17 is 0 dB or less, the control unit 20 sets the input attenuation unit 14 a to be executed by the
digital signal processing program in the DSP 14 to 0 dB, and the tone control unit 14 b The level
increase is not set, and the output gain adjustment unit 14c is set to -20 dB.
[0017]
FIG. 3 is a diagram showing an operation state of the DSP 14 when the setting of the tone control
adjustment key 17 is 10 dB or less. In FIG. 3, when the gain increase frequency band is set to 10
dB with this tone control adjustment key 17, at this time, the control unit 20 attenuates the input
of the DSP 14 after satisfying the condition of -.infin. -10 dB is set in the section 14a, the tone
control section 14b is set so that the low band which is the setting band is increased by 10 dB,
and the output gain adjusting section 14c is -10 dB relative to -.infin. Set to an increased value.
[0018]
Next, the case where the setting amount is changed to 12 dB from the setting state of the tone
control adjustment key 17 shown in FIG. 3 will be described.
[0019]
FIG. 4 is a diagram showing an operation state of the DSP 14 when the setting of the tone control
adjustment key 17 is changed to 12 dB.
In FIG. 4, the control unit 20 sets -12 dB for the input attenuation unit 14a in the DSP 14, sets
the tone control unit 14b to increase the gain in the low band by 12 dB, and sets the output gain
adjustment unit 14c to the volume volume value. The value is set to -8 dB which is relatively
increased by 12 dB.
[0020]
The operation on the time axis of control unit 20 in the operation shown in FIGS. 3 and 4 will be
described. For example, when the tone control device of this embodiment is provided in a stereo
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audio device, the control unit 20 executes various controls such as power supply system
management and display system management in addition to control of the tone control unit 14b,
One control cycle is several tens of ms. Further, when the control time of the tone control device
is limited within this one control cycle, each control of the input attenuator 14a, the tone
controller 14b and the output gain adjuster 14c of the DSP 14 is divided into a plurality of
control cycles. There is a thing.
[0021]
FIG. 5 is a diagram showing a case where control of a series of processes is performed in this one
control cycle. In FIG. 5, after the setting of the input attenuator 14a is changed from -10 dB to 12 dB, the setting of the tone control unit 14b is changed from +10 dB to +12 dB. The change
from -10 dB to -8 dB in the output gain adjustment unit 14c may be performed at any timing, but
can be performed in a continuous control cycle of the control unit 20 to ensure an instantaneous
change without a sense of discomfort in hearing.
[0022]
Next, the case where the setting is changed to 8 dB by the tone control adjustment key 17 from
the setting state shown in FIG. 4 will be described. FIG. 6 is a diagram for explaining an operation
state when the setting is changed to 8 dB by the tone control adjustment key 17 from the setting
state shown in FIG. In FIG. 6, the control unit 20 sets -8 dB in the input attenuation unit 14a of
the DSP 14, sets the tone control unit 14b so that the low band which is the setting band
increases by 8 dB, and outputs the output gain adjustment unit 14c. It is set to -12 dB which is 8
dB relatively increased from the value of the volume control.
[0023]
Next, the operation on the time axis of the control unit 20 in this operation will be described. FIG.
7 is a diagram showing a case where only control of one process is performed in one control
cycle. In FIG. 7, after changing the setting of the tone control unit 14b from +10 dB to +8 dB, the
setting of the input attenuator 14a is changed from -10 dB to -8 dB. The change from -10 dB to 12 dB of the output gain adjustment unit 14c may be any timing. However, by performing the
control in a continuous control cycle in the control unit 20, it is possible to ensure an
instantaneous change without a sense of discomfort in hearing. In the operation shown in FIGS. 2
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to 7, the setting of the tone control adjustment key 17 is 12 dB. However, generally, when X (> 0)
dB is set, the control unit 20 is satisfied after satisfying the following expression (1). The set
value of the input attenuator 14a controlled by can be expressed by the following equation (2).
Further, the set value of the output gain adjustment unit 14c can be expressed by the following
equation (3).
[0024]
−∞ ≦ volume volume value ≦ −X (1) input attenuation amount = −X (X ≧ 0) (2) setting value
of the output gain adjustment unit 14 c = (volume volume value) + X (3) However, As is clear
from the equation (1), if the volume value is -X (0 0) dB, the maximum controllable gain increase
amount is X dB, and if the volume volume value is maximum 0 dB, no gain increase is possible. It
becomes possible. This maintains high sound quality in terms of hearing, the maximum input
level to the amplifier 18 is equal to the maximum input level of the A / D converter 13, and the
level management process is facilitated.
[0025]
Further, although the gain increasing band is set to the low band in the operations shown in FIGS.
2 to 7, any band may be used.
[0026]
As apparent from the above description, according to the tone control device of the present
invention, the gain of the input digital audio signal is attenuated in the previous stage in response
to the gain increase in the tone control means, and the output of the tone control means Since
the gain of the signal is adjusted at a later stage, and the set amount of the tone control means,
the input attenuation means and the output gain adjustment means is controlled by the control
means according to the gain variable amount in this tone control means and this change history
The generation of abnormal noise can be prevented and the input / output level can be kept
equal without providing a clip margin which causes the performance deterioration at the time of
digital conversion.
[0027]
Brief description of the drawings
[0028]
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1 is a block diagram of a tone control device according to an embodiment of the present
invention.
[0029]
Fig. 2 is a characteristic diagram showing the operating state of the DSP when the setting of the
tone control adjustment key is less than 0 dB in the same embodiment.
[0030]
Fig. 3 is a characteristic diagram showing the operation state of the DSP when the setting of the
tone control adjustment key is 10 dB in the same embodiment.
[0031]
Fig. 4 is a characteristic diagram showing the operation state of the DSP when the setting of the
tone control adjustment key is 12 dB in the same embodiment.
[0032]
5 is a timing chart in the case of controlling a series of processes in a control cycle in the same
embodiment.
[0033]
Fig. 6 is a characteristic diagram showing the operating state of the DSP when the tone control
adjustment key setting is 8 dB in the same embodiment.
[0034]
7 is a timing chart in the case of controlling only one process in a control cycle in the same
embodiment.
[0035]
8 is a block diagram showing the configuration of a conventional tone control device
[0036]
Explanation of sign
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[0037]
11 sound source 12 LPF 13 A / D converter 14 DSP 14 a input attenuation unit 14 b tone
control unit 14 c output gain adjustment unit 16 LPF 17 tone control adjustment key 18
amplifier 19 speaker 20 control unit
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