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JPH1117474

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DESCRIPTION JPH1117474
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
variable gain device for changing gain in digital signal processing, and more particularly to a
variable gain device used as a volume function of various audio devices.
[0002]
2. Description of the Related Art FIG. 5 shows the configuration of the main part of a
conventional variable gain device. Here, a portion for multiplying the volume function of the
audio device by digital signal processing is illustrated. In the figure, reference numeral 501
denotes a digital signal processor (hereinafter referred to as a DSP) including a coefficient update
processing unit 501a and a multiplication processing unit 501b. Reference numeral 502 denotes
a control unit such as a microcomputer that controls the DSP 501, and reference numeral 503
denotes a volume adjustment key connected to the control unit 502. The control unit 502 sets a
desired coefficient value for each desired volume, and stores the desired coefficient value in the
memory.
[0003]
FIG. 6 shows the contents of each value set by the control unit 502. Here, respective values of
volume value, volume gain value (−dB), desired coefficient value (dec), and coefficient value
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difference (dec) are set, and are stored in a memory (not shown) in the control unit 502. Besides,
gain update time (ms) is also stored. Specifically, a 16-bit fixed-point coefficient is used, the
maximum gain is 0 dB, and the coefficient value at that time is 7FFFh = 32767. Also, the volume
gain value is a change step every 2 dB.
[0004]
Next, the operation of the variable gain device of FIG. 5 will be described. When the volume is
changed by the volume adjustment key 503, the control unit 502 selects the corresponding
"desired coefficient value" from the information in the "volume value" from the information in the
memory, and transfers it to the coefficient update processing unit 501a of the DSP 501. The
coefficient update processing unit 501a repeatedly executes addition or subtraction of 1 only
once in one sampling period until the multiplication coefficient value of the multiplier (not
shown) in the multiplication processing unit 501b becomes equal to the "desired coefficient
value". Do.
[0005]
FIG. 7 is a flowchart showing conventional coefficient update processing. First, it is determined
whether the multiplication coefficient value matches the desired coefficient value (step 701). If
they match, the coefficient update process ends. If the multiplication coefficient value does not
match the desired coefficient value, the multiplication coefficient value is incremented by 1 to
make it a new multiplication coefficient value (step 702), and the process is ended. The time
required for this update is expressed by | multiplication coefficient value at the start of
update−desired coefficient value | × 1 sampling cycle (in this case, the multiplication coefficient
value at the start of update is the desired coefficient value at the previous update) equal). For
example, if the sampling frequency is 44.1 kHz, the update time between each volume position is
the "gain update time" of FIG.
[0006]
In this variable gain device, as is clear from FIG. 6, the update time largely differs depending on
the volume position, and a smooth change in hearing was not obtained. The reason is generally
that the change in gain of the volume function is a logarithmic change, that is, a linear change
due to a dB value, while the update of the coefficient value is a linear change due to addition or
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subtraction.
[0007]
The present invention solves the above-mentioned conventional problems and provides a
variable gain device capable of enhancing responsiveness, making the update time according to
the volume position substantially constant, and smoothing the auditory change during the
update. Intended to provide.
[0008]
SUMMARY OF THE INVENTION In order to solve this problem, according to the present
invention, when controlling the gain of an input signal with a digital signal processor, the
multiplication coefficient value for changing the gain does not match the updated desired
coefficient value. At the same time, the multiplication coefficient value is configured to be
updated by adding or subtracting a coefficient variation amount once in one sampling period to
or from the multiplication coefficient value.
[0009]
As a result, it is possible to obtain a variable gain device capable of maintaining the update time
according to the volume position substantially constant and performing smooth hearing change
even during the update of the volume change.
[0010]
According to a first aspect of the present invention, there is provided a multiplication processing
unit for multiplying an input signal by a multiplier coefficient value to change a gain, and
updating a multiplication coefficient value associated with the multiplication processing. A digital
signal processor (DSP) incorporating a coefficient update processing unit and a control unit for
controlling the digital signal processor, wherein the multiplication coefficient value matches the
desired coefficient value set according to the request for gain change In the variable gain device
for updating the multiplication coefficient value, when the multiplication coefficient value does
not match the updated desired coefficient value, the coefficient update processing unit is
responsive to the magnitude relationship between the multiplication coefficient value and the
desired coefficient value. Thus, the multiplication coefficient value is updated by adding or
subtracting the coefficient variation amount to the multiplication coefficient value once in one
sampling period, and a simple update such as addition or subtraction is performed. While using
the stage, it can update time corresponding to the volume located approximately constant, an
effect that it is possible to smooth the hearing variation being updated.
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[0011]
In the digital signal processor according to the second aspect of the invention, when the amount
of change in gain that causes an auditory smooth change is A (dB), the coefficient change amount
after update is the desired coefficient value before update × It is intended to satisfy [{10 ^ (A /
20)}-1] or less and the desired coefficient value before updating x [1- {10 ^ (-A / 20)}] or less, and
By looking at the conditions, it is possible to smooth the change in the sense of hearing.
[0012]
In the invention according to claim 3, in the coefficient update processing unit, a coefficient
change amount storage memory in which the coefficient change amount selected by the control
unit is stored, and the desired coefficient value selected by the control unit It has a desired
coefficient storage memory to be stored, and has an effect that it becomes possible to easily and
quickly update the multiplication coefficient value.
[0013]
Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to
4.
FIG. 1 shows the configuration of a variable gain device according to the present invention.
In the following, an example applied to the volume function of an audio device will be described.
[0014]
A sound source 101 outputs an analog audio signal.
Reference numeral 102 denotes a low pass filter (hereinafter referred to as "LPF") for cutting the
high frequency band of the sound source 101, and reference numeral 103 denotes an A / D
converter for converting an output signal of the LPF 102 into a digital signal.
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Reference numeral 104 denotes a DSP (Digital Signal Processor) that performs digital signal
processing, and includes a coefficient update processing unit 104 a and a multiplication
processing unit 104 b.
Reference numeral 105 denotes a D / A converter connected to the DSP 104, which converts the
output of the DSP 104 into an analog signal (audio signal).
Reference numeral 106 denotes an LPF connected to the D / A converter 105, which removes
harmonic components in the output signal of the D / A converter 105. An amplifier 107 is
connected to the LPF 106 to perform voltage amplification and power amplification of an analog
audio signal, and a speaker 108 connected to the amplifier 107 to perform electro-acoustic
conversion. Reference numeral 109 denotes a volume adjustment key operated by the user,
which instructs to change the gain of the reproduction signal by the sound source 101.
Reference numeral 110 denotes a control unit such as a microcomputer that controls the DSP
104. In the present embodiment, 44.1 kHz is used as the sampling frequency.
[0015]
FIG. 2 shows the detailed configuration of the coefficient update processing unit 104 a and the
multiplication processing unit 104 b of the DSP 104. The coefficient update processing unit 104a
includes a coefficient variation storage memory 201 and a desired coefficient storage memory
202, and the multiplication processing unit 104a includes a multiplier 203 for changing the gain.
Further, a memory 204 shared by the coefficient update processing unit 104 a and the
multiplication processing unit 104 b is provided. The coefficient variation storage memory 201
and the desired coefficient storage memory 202 are both 16-bit coefficient memories. The
multiplier 203 is a 16-bit fixed point coefficient, and the coefficient value at the maximum gain of
0 dB is 7FFF (hex) = 32767 (dec). In the present embodiment, the volume function has a
maximum gain of 0 dB, and each volume value is a change step every 2 dB.
[0016]
In a memory (not shown) in the control unit 110, as shown in FIG. 3, a coefficient change amount
Sn set so as to satisfy first to fourth conditions to be described later corresponding to the volume
value n is desired The coefficient value Dn is stored. Further, in addition to the contents shown in
FIG. 6, the coefficient difference at the time of falling (dec) and the gain update time (ms), the
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coefficient difference at the time of rising (dec) and the gain update time (ms) are stored. In the
case of the present embodiment, the coefficient change amount Sn is determined so that the gain
update time can be made constant in the range of 0.1 to 0.3 ms with one step change of each
volume value, that is, 2 dB gain change. ing. Further, the coefficient change amount Sn is set so
that the gain change per sampling period is 0.5 dB or less so that a smooth change in the sense
of hearing can be obtained.
[0017]
The amount of coefficient change to satisfy the first to fourth conditions under the relationship
between adjacent volume positions n ′ = n + 1 and n ′ = n−1 for each gain value Vn (dB) at
volume position n Define Sn and the desired coefficient value Dn.
[0018]
The first condition is that the desired coefficient value is Dn, the adjacent volume position is n ',
the desired coefficient is Dn', and the coefficient change amount is Sn ', | Dn−Dn ′ | = Sn ′ ×
m (m: To meet the natural number).
[0019]
The second condition is to satisfy Sn = Sn ′ × m (m: natural number) Sn = Sn ′ / m (m: natural
number) between the coefficient change amount Sn and the coefficient change amount Sn ′.
[0020]
The third condition is that the desired coefficient value Dn is the closest approximation value to
realize the gain value Vn, and in this case, the gain update required time Tn ′ from the volume
position n to n ′ is the following equation Calculated by
[0021]
Tn '=. Vertline.Dn-Dn'.vertline. / Sn'.times. Sampling period Further, as a fourth condition, the
coefficient change amount Sn' is to satisfy the following formula.
When it is assumed that the amount of change in gain that produces a smooth change in the
sense of hearing is A (dB), Sn ′ <Dn × [{10 ^ (A / 20)} − 1] is satisfied, and Sn ′ <Dn × [1 -It
is necessary to satisfy {10 ^ (-A / 20)}.
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[0022]
Next, the operation of the variable gain device of FIG. 1 will be described.
Further, the coefficient update processing will be described with reference to the flowchart of
FIG.
[0023]
Usually, the digital audio signal is input to the multiplication processing unit 104b in the DSP
104, multiplied by the multiplication coefficient value in the multiplier 203, and output after the
gain is varied.
The multiplication coefficient value is stored in a multiplication coefficient value storage memory
204 in the DSP 104.
[0024]
First, when a user performs a volume operation (operation of the volume operation key 109),
volume value information from the volume operation key 109 is transferred to the control unit
110.
The control unit 110 selects the coefficient change amount and the desired coefficient value
corresponding to the volume value based on the volume value information. Next, the control unit
110 transfers the selected coefficient change amount to the coefficient change amount storage
memory 201 of the DSP 104, and transfers the selected desired coefficient value to the desired
coefficient value storage memory 104a.
[0025]
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Then, as shown in FIG. 4A, the coefficient update processing unit 104a compares the contents of
each storage memory of the multiplication coefficient value and the desired coefficient value
(step 401), and if different (multiplication coefficient value ≠ desired The coefficient value) and
its large and small relationships are determined (step 402). When [multiplication coefficient
value <desired coefficient value], addition processing of [multiplication coefficient value +
coefficient change amount] is performed, and the result is set as a multiplication coefficient value
(step 403), and the coefficient update processing is ended. If [multiplication coefficient value>
desired coefficient value], subtraction processing of [multiplication coefficient value-coefficient
change amount] is performed, and the result is set as a multiplication coefficient value (step
404), and the coefficient updating process is ended. The multiplication coefficient value is
updated by adding or subtracting the coefficient variation amount to the multiplication
coefficient value, and the result is stored in the multiplication coefficient storage memory 204.
[0026]
Further, as shown in FIG. 4 (b), the multiplication processing unit 104b multiplies the input
signal by the updated multiplication coefficient value, and sets it as an output signal (step 405).
The gain changes due to this multiplication process. The above processing of the coefficient
update processing unit 104a and the multiplication processing unit 104b is performed only once
in one sampling cycle.
[0027]
For example, when the volume falls from −6 dB to −8 dB, volume position: n = 3 multiplication
coefficient value at the start of updating the gain: Dn = D3 = 16384 (fourth stage in FIG. 3)
coefficient variation: Sn ′ = Sn + 1 = S4 = 256 (5th stage in FIG. 3) The desired coefficient value:
Dn '= D4 = 12800 (5th stage in FIG. 3) is set. In this case, the first condition, | Dn−Dn ′ | = Sn
′ × m (where m is a natural number) | 16384-12800 | = 3584 = 256 × 14
[0028]
When the volume rises from −8 dB to −6 dB, volume position: n = 4 multiplication coefficient
value at the start of the update of the gain: Dn = D4 = 12800 (the fifth step in FIG. 3) coefficient
variation: Sn '= S (n-1) = S3 = 512 (fourth stage in FIG. 3) The desired coefficient value: Dn' = D3 =
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16384 (fourth stage in FIG. 3) is set. In this case, the first condition, | Dn−Dn ′ | = Sn ′ × m
(m is a natural number) | 12800-16384 | = 3584 = 512 × 7
[0029]
Therefore, under the second condition, when n = 3 and n '= (n + 1), Sn = S (n + 1) × m (m is a
natural number) 512 = 256 × 2, and n = 4 and n' = (n). n−1) when Sn = S (n−1) / m (m is a
natural number) 256 = 512 /2
[0030]
Furthermore, D3 and D4 satisfy the first and second conditions, and are the closest
approximations to realize -6 dB and -8 dB, which satisfy the third condition.
[0031]
In this case, the time required for the volume to fall from −6 dB to −8 dB, Tn ′ = | Dn−Dn ′ |
/ Sn ′ × sampling period, n = 3 ′, n ′ = [n + 1], when T4 = | 16384-12800 // 256/44100 =
0.0032.
The time required for the volume to rise from −8 dB to −6 dB is n = 4 ′, n ′ = [n−1] when T3
= | 12800-16384 | / 512/44100 = 0.
0016
[0032]
Furthermore, in order to bring about a smooth change in the sense of hearing, the amount of
change in gain per sampling period is set to 0.5 dB, and under the fourth condition, n = 3, n '= n +
1, and Sn' <Dn × [n]. 1− {10 ^ (− A / 20)}] 256 <16384 × [1− {10 ^ (− 0.5 / 20)}] = 916 and
n = 4 ′, n ′ = n−1 o'clock Sn It will be set and satisfy | fills <= Dnx [{10 ^ (A / 20)}-1] 512
<12800x [{10 ^ (0.5 / 20)}-1] = 758.
[0033]
Similarly to the above, all the values shown in FIG. 3 satisfy the first to fourth conditions, and as a
result, while the simple method of addition or subtraction uses the update method, the update
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time according to the volume position is 0.1 to 0 It can be kept in the range of .3 ms to smooth
the change in hearing during updating of the volume function.
[0034]
As described above, in general, since the gain change of the volume function is a logarithmic
change, that is, a linear change in decibel (dB) value, the amount of change in gain varies
depending on the volume position.
That is, the amount of gain change when updating from 0 dB to -6 dB is 1-0.5 = 0.5.
In the case of -20 dB to -26 dB, the amount of change in gain is 0.1-0.05 = 0.05, even with the
same amount of volume change of 6 dB.
[0035]
According to the present invention, the coefficient updating process takes a method of equalizing
the desired coefficient value by adding or subtracting the coefficient variation amount only once
in one sampling cycle to the current multiplication coefficient value, so The coefficient change
amount Sn is determined for each gain value Vn (dB) in n, and when the gain change is large, the
coefficient change amount is large, and when the gain change is small, the coefficient change
amount is small to update the gain. The time required can be adjusted and can be approximately
constant for any volume position. Further, by satisfying the first to third conditions, it is possible
to cope with a set of coefficient change amounts Sn at the volume position Vn and a desired
coefficient value Dn at the volume rise time and the volume fall time. Furthermore, by satisfying
the fourth condition, since it is aurally perceived as something that has changed smoothly by
repeating minute changes, it is possible to prevent the generation of abnormal noise at the time
of volume operation.
[0036]
From the above, it is possible to keep the update time according to the volume position
substantially constant while using a simple update method such as addition or subtraction, and
by the digital signal processing excellent in responsiveness which can bring about smooth
hearing change during update. A variable gain device can be provided.
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[0037]
As described above, according to the present invention, while using a simple updating method
such as addition or subtraction, the updating time according to the volume position can be made
almost constant, and the aural change during updating can be smoothed. It is possible to obtain
an effect that it is possible to configure a variable gain device with excellent responsiveness.
[0038]
Brief description of the drawings
[0039]
1 is a block diagram showing the configuration of a variable gain device according to the present
invention
[0040]
FIG. 2 is a block diagram showing details of the coefficient update processing unit and the
multiplication processing unit of FIG.
[0041]
FIG. 3 is an explanatory view showing data contents such as coefficients stored in the control unit
of FIG. 1
[0042]
Flow chart showing the coefficient updating process according to the present invention
[0043]
5 is a block diagram showing the configuration of the main part of the conventional variable gain
device
[0044]
6 is an explanatory view showing the contents of each value set by the control unit of FIG. 5
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[0045]
FIG. 7 is a flowchart showing conventional coefficient updating processing
[0046]
Explanation of sign
[0047]
101 sound source 103 A / D converter 104 digital signal processor (DSP) 104a coefficient
update processing unit 104b multiplication processing unit 105 D / A converter 201 coefficient
variation storage memory 202 desired coefficient storage memory 203 multiplier 204 memory
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