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DESCRIPTION JP2010206298

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DESCRIPTION JP2010206298
To correct an audio signal with a frequency characteristic suitable for environment and a signal
level. A recording device includes an audio signal correction unit and an audio signal processing
unit. The audio signal correction unit 16 corrects the level of the audio signal and flattens the
frequency characteristic of the audio signal based on the recording mode, for the audio signal
supplied from the microphone. The correction control unit 13 causes the audio signal correction
unit 16 to adjust the level of the audio signal so that the level of the audio signal falls within the
range between the lower limit value and the upper limit value of the target level for each
recording mode. Then, the absolute value of the level of the audio signal that becomes maximum
within a predetermined period is used as a reference value to attenuate according to the passage
of time, and when the audio signal whose level exceeds the reference value is input, the reference
value is The absolute value of the level of the voice signal that exceeds the level is taken as a new
reference value. [Selected figure] Figure 3
Recording apparatus, recording method, audio signal correction circuit and program
[0001]
The present invention relates to a recording apparatus, a recording method, an audio signal
correction circuit, and a program, which are suitably applied to the case of correcting voice
according to the environment such as a conference room or a hall, for example.
[0002]
Conventionally, a small recording device for recording the contents of a conference or lecture has
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been used.
Such a recording device includes, for example, a miniaturized microphone, a DSP (Digital Signal
Processor), and the like. Then, predetermined processing is performed on the audio signal
according to the recording mode by automatic gain control (AGC: Automatic Gain Control). Since
the AGC coefficient for changing the AGC is set by a fixed constant, the user manually corrects
the frequency characteristics of the microphone.
[0003]
Patent Document 1 discloses a technique of interlocking signal levels such that audio
characteristics suitable for outdoor or indoor shooting conditions are obtained.
[0004]
Unexamined-Japanese-Patent No. 5-161101
[0005]
By the way, conventionally, a unidirectional microphone incorporated in a recording apparatus
has a small aperture, and generally, the frequency characteristic of such a microphone has a low
response in the low frequency range.
In a meeting or the like, if the response in a band lower than the voice band is low, the level of
unnecessary components such as fan noise of a projector may be suppressed, and the voice may
be relatively easy to hear.
However, in the case of recording an instrument or the like, flat frequency characteristics are
required over a wide band, so the low frequency range of the recorded voice may be insufficient.
Therefore, the scene which can be recorded with an appropriate characteristic may be limited. In
a meeting or the like, a small volume of audio is amplified by the AGC to an appropriate volume
that is easy to hear and compressed to a constant volume. On the other hand, although music is
required to inflate the volume, when using a conventional recording device, even small sounds
close to silence are automatically amplified, so that the entire volume is likely to be recorded at a
flat volume.
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[0006]
The present invention has been made in view of such a situation, and its object is to correct an
audio signal with a frequency characteristic suitable for the environment and a signal level.
[0007]
The present invention flattens the frequency characteristics of an audio signal supplied from a
microphone based on a recording mode in which the frequency characteristics of the audio
signal and the amount of correction of the level are determined. Correct the level.
Also, based on the lower limit value and the upper limit value of the target level predetermined
for each recording mode, when the level of the audio signal falls below the lower limit value of
the target level, the level of the audio signal exceeds the lower limit value of the target level. So,
adjust the level of the audio signal. On the other hand, when the level of the audio signal exceeds
the upper limit value of the target level, the level of the audio signal is adjusted so that the level
of the audio signal falls below the upper limit value of the target level. Next, the absolute value of
the level of the audio signal that is maximum within a predetermined period is used as a
reference value, and the reference value is attenuated according to the passage of time. Then,
when an audio signal whose audio signal level exceeds the reference value is input, the absolute
value of the audio signal level exceeding the reference value is used as a new reference value.
[0008]
By doing this, it becomes possible to adjust the level of the audio signal appropriately according
to the recording mode set by the user and correct the frequency characteristic of the audio
signal.
[0009]
According to the present invention, the user can set the recording mode according to the scene
to be recorded, and based on the recording mode, the frequency characteristic and the level of
the audio signal are corrected.
For this reason, it is possible to obtain an audio signal of an appropriate level with frequency
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characteristics suitable for the environment, and it is possible to easily obtain an audio of sound
quality intended by the user.
[0010]
It is a block diagram which shows the internal structural example of the sound recording
apparatus in one embodiment of this invention. It is a block diagram which shows the internal
structural example of the main-control part in one embodiment of this invention. It is a block
diagram which shows the internal structural example of the audio | voice signal correction |
amendment part in one embodiment of this invention. It is an explanatory view showing an
example of frequency characteristic amendment in a 1 embodiment of the present invention. It is
explanatory drawing which shows the example of the frequency characteristic of the audio |
voice signal before and behind correction | amendment in one embodiment of this invention. It is
explanatory drawing which shows the example of the sound recording mode in one embodiment
of this invention. FIG. 8 is an explanatory view showing an example of matching the signal level
of the audio signal to the target level lower limit value in the embodiment of the present
invention. FIG. 7 is an explanatory view showing an example of adjusting the signal level of the
audio signal within the range of the target level upper limit value and the lower limit value in the
embodiment of the present invention. It is explanatory drawing which shows the example which
changes a reference value by fixed attenuation amount from the maximum value of the signal
level in one embodiment of this invention. FIG. 7 is an explanatory view showing an example of
changing the attenuation amount to change the reference value according to the maximum value
of the signal level in the embodiment of the present invention. FIG. 14 is an explanatory view
showing an example of comparing signal levels for each of left and right channels and changing
signal levels of the left and right channels in another embodiment of the present invention.
[0011]
Hereinafter, the best mode for carrying out the invention (hereinafter referred to as an
embodiment). Will be described. The description will be made in the following order. 1. 1.
Embodiment (correction of frequency characteristics and signal level of audio signal: an example
of flattening the frequency characteristics of audio signal to bring the signal level within a target
level range) Modified example
[0012]
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<1. Embodiment> [Example of internal configuration of recording device]
[0013]
Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1
to 10. In the present embodiment, an example applied to the recording device 1 that corrects the
level of an audio signal to be recorded according to a predetermined recording mode will be
described.
[0014]
FIG. 1 shows an example of the internal configuration of the recording device 1 of this
embodiment. The recording device 1 includes microphones 2R and 2L that generate analog audio
signals of left and right two channels, and a codec unit 3 that converts analog audio signals into a
predetermined digital format. For example, linear PCM (Pulse Code Modulation) is used as a
format supported by the codec unit 3.
[0015]
In addition, the recording device 1 corrects the signal level and the frequency characteristic of
the digital audio signal supplied from the codec unit 3 according to a predetermined recording
mode, and the main control unit 4 corrects the signal level and the frequency characteristic. A
recording unit 5 for recording the digital audio signal on the recording medium 11 is provided.
For example, a system LSI is used for the main control unit 4, and a flash memory is used for the
recording medium 11, for example. Hereinafter, with respect to the audio signals supplied from
the microphones 2R and 2L, a parameter for determining the correction amount of the frequency
characteristic and the level of the audio signals is referred to as a "recording mode". There are
five types of recording modes in this example as described later.
[0016]
The recording device 1 further includes an operation unit 7 that allows the user to arbitrarily set
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the recording mode, and a display unit 8 that displays the set recording mode or displays that
recording is in progress. For example, a key button is used for the operation unit 7, and a liquid
crystal display panel is used for the display unit 8, for example.
[0017]
Further, the recording device 1 includes a power supply 6 for supplying power to the codec unit
3, the main control unit 4 and the recording unit 5. Further, the recording device 1 includes a
speaker 9 and an earphone 10 which emit sound. The codec unit 3 converts a digital audio signal
into an analog audio signal, and supplies an audio signal to the speaker 9 and the earphone 10
via an amplifier (not shown). As a result, the speaker 9 and the earphone 10 can emit sound.
However, the recording device 1 can not only read out the digital audio signal from the recording
unit 5, but can also emit sound to the speaker 9 and the earphone 10 in real time without
passing through the recording unit 5.
[0018]
[Internal Configuration Example of Main Control Unit] FIG. 2 shows an internal configuration
example of the main control unit 4. The main control unit 4 includes an audio signal processing
unit 12 that adjusts the level and frequency characteristics of the digital audio signal supplied
from the codec unit 3. Further, the main control unit 4 includes a sub control unit 13 that
records a digital audio signal on the recording medium 11 via the recording unit 5 and reads a
digital audio signal from the recording medium 11 via the recording unit 5. For example, a DSP is
used for the audio signal processing unit 12, and a CPU is used for the sub control unit 13, for
example. The audio signal processing unit 12 can appropriately process the audio signal
according to the recording mode by changing the AGC coefficient and the filter coefficient.
Furthermore, data after processing can be compressed by encoder processing such as MP3.
[0019]
[Example of Internal Configuration of Audio Signal Processing Unit] FIG. 3 shows an example of
the internal configuration of the audio signal processing unit 12. The audio signal processing
unit 12 is a block incorporated in the recording device 1 as an audio signal correction circuit.
The audio signal processing unit 12 corrects the frequency characteristic of the digital audio
signal to an appropriate frequency characteristic and / or corrects the level of the audio signal
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according to the pre-processing unit 15 that preprocesses the digital audio signal and the set
recording mode. An audio signal correction unit 16 for correcting is provided.
[0020]
Further, the audio signal processing unit 12 includes a selection unit 17 that supplies the sub
control unit 13 with a digital audio signal. The selection unit 17 selects and outputs a digital
audio signal whose frequency characteristic and signal level have been adjusted through the
audio signal correction unit 16 or a digital audio signal which is not subjected to any processing,
or a recording mode as a fader Adjust the volume at the time of switching.
[0021]
Further, the audio signal processing unit 12 includes a correction control unit 18 that performs
predetermined control on the preprocessing unit 15, the audio signal correction unit 16, and the
selection unit 17. The control of the correction control unit 18 mainly differs depending on the
on / off of the recording mode to be switched by the input operation of the operation unit 7 or
the type of the recording mode to be set.
[0022]
The audio signal correction unit 16 sets the frequency characteristics of the audio signal
appropriate for the audio signal supplied from the microphones 2R and 2L based on the
recording mode in which the correction amount of the frequency characteristic and the level of
the audio signal is determined. And / or correct the level of the audio signal.
[0023]
The audio signal correction unit 16 is a fifth correction unit that increases or decreases the signal
level of the digital audio signal according to the first correction unit 21 to the fourth correction
unit 24 that corrects predetermined frequency characteristics, and the set recording mode. A unit
25 is provided.
An example of the frequency characteristics corrected by the first correction unit 21 to the
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fourth correction unit 24 will be described with reference to FIG. 4 described later. Further, an
example of the signal level of the digital audio signal corrected by the fifth correction unit 25 will
be described with reference to FIGS. 6 to 10 described later.
[0024]
When the level of the audio signal falls below the lower limit value of the target level based on
the lower limit value and the upper limit value of the target level predetermined for each
recording mode, the correction control unit 18 determines that the audio signal level is the target
level. The audio signal correction unit 16 adjusts the level of the audio signal so as to exceed the
lower limit value. On the other hand, when the level of the audio signal exceeds the upper limit
value of the target level, the correction control unit 18 outputs the level of the audio signal to the
audio signal correction unit 16 so that the level of the audio signal falls below the upper limit
value of the target level. Let me adjust. Then, the correction control unit 18 uses the absolute
value of the level of the audio signal that is maximum within a predetermined period as a
reference value, and attenuates the reference value as time passes. Thereafter, when an audio
signal whose audio signal level exceeds the reference value is input, the correction control unit
18 sets the absolute value of the audio signal level above the reference value as a new reference
value.
[0025]
FIG. 4 shows an example of the frequency characteristic corrected by the first correction unit 21
to the fourth correction unit 24. 4 and 5 show examples of frequency characteristic correction
with the horizontal axis representing frequency [Hz] and the vertical axis representing power
[dB] for each of the first correction unit 21 to the fourth correction unit 24.
[0026]
FIG. 4A shows an example of the frequency characteristic corrected by the first correction unit
21. The first correction unit 21 has a function of raising the signal level of the frequency
characteristic (low range) of the range 31. For example, an Infinite impulse response (IIR) bus
shelving filter is used for the first correction unit 21.
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[0027]
FIG. 4B shows an example of the frequency characteristic corrected by the second correction unit
22. The second correction unit 22 has a function to increase / decrease and finely adjust the
signal level of the frequency characteristic (middle to low frequency range) of the tone range 32.
For example, an IIR equalizer filter is used for the second correction unit 22.
[0028]
FIG. 4C shows an example of the frequency characteristic corrected by the third correction unit
23. The third correction unit 23 has a function of cutting the signal level of the frequency
characteristic of the sound range 33 (ultra low frequency band below the audible band). As a
result, an unnecessary very narrow low band that causes noise is cut. For example, an IIR type
high pass filter (HPF: High Pass Filter) is used for the third correction unit 23.
[0029]
FIG. 4D shows an example of the frequency characteristic corrected by the fourth correction unit
24. The fourth correction unit 24 has a fine adjustment function by increasing or decreasing the
signal level of the frequency characteristic (high band) of the sound range 34. For example, an
IIR equalizer filter is used for the fourth correction unit 24.
[0030]
FIG. 4E shows an example of the frequency characteristic correction that the first correction unit
21 to the fourth correction unit 24 correct. The first correction unit 21 to the fourth correction
unit 24 respectively perform frequency characteristic correction on the tone ranges 31 to 34
shown in the drawing.
[0031]
FIG. 5 shows an example of the frequency characteristics of the audio signal before and after
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correction. FIG. 5A shows an example of the frequency characteristic of the audio signal before
correction. At this time, since the signal level of the digital audio signal input to the audio signal
processing unit 12 is not uniform for each frequency, it may sound that the low band is
insufficient at the time of sound emission.
[0032]
FIG. 5B shows an example of the frequency characteristic of the audio signal after correction. The
first to fourth correction units 21 to 24 included in the sound signal correction unit 16 cut
unnecessary low bands from the sound signal and flatten the signal level of the digital sound
signal in the audible area, Sounds like the sound input by the user at the time of sound emission.
[0033]
FIG. 6 shows an example of the recording mode set by the recording device 1.
[0034]
FIG. 6A shows an example of the recording mode.
The recording device 1 of this example prepares a plurality of recording modes in order to
change the recording sensitivity of the microphones 2R and 2L. In the recording mode, a first
recording mode serving as a reference of sensitivity is defined while keeping the frequency
characteristics of the audio signal collected by the microphones 2R and 2L. In the recording
mode, a second recording mode in which the sensitivity of the microphones 2R and 2L is made
higher than in the first recording mode, and a third recording mode in which the sensitivity of
the microphones 2R and 2L is lower than the first recording mode. The recording mode is
defined. Further, in the recording mode, a fourth recording mode for correcting the level of the
audio signal is defined while the frequency characteristic of the audio signal is corrected to a
frequency characteristic appropriate for the recording scene by the filter processing. Then, one
of the first to fourth recording modes is set by the user.
[0035]
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Specifically, the recording device 1 prepares five types of recording modes (a conference mode, a
high sensitivity mode, a dictation mode, a music mode and a manual mode). Since the sensitivity
of the microphones 2R and 2L required for each recording mode is different, the fifth correction
unit 25 adjusts the signal level of the digital audio signal for each recording mode.
[0036]
The conference mode is suitable for recording a conversation in a conference room or the like,
and corresponds to the first recording mode described above. At this time, the sensitivity of the
microphones 2R and 2L is moderate, and becomes the reference signal level in the other
recording mode.
[0037]
The high sensitivity mode has a function of largely amplifying and recording even small sounds,
and corresponds to the second recording mode described above. The high sensitivity mode is
suitable for recording small meetings in a conference mode or for recording meetings etc. in a
large conference room without using PA (Public Address).
[0038]
The dictation mode has a function of automatically adjusting the signal level at the time of
recording so as to obtain the same volume as possible, and corresponds to the above-described
third recording mode.
[0039]
Music mode is a function that is corrected so that the frequency characteristic is flat over a wider
band than voice so that there is no sense of discomfort when recording a performance such as a
musical instrument, and the sound is recorded without loss of intonation And corresponds to the
fourth recording mode described above.
If you record music while other modes are set, the tonality of the sound may be lost and the
sound may be flat. Also, depending on the instrument to be recorded, the sound may be recorded
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with shaking. Therefore, a dedicated music mode is provided to record the performance of an
instrument or the like.
[0040]
The manual mode is a mode that changes the gain (amplification factor) of the microphones 2R
and 2L according to the preference of the user regardless of other recording modes. In the
manual mode, when the user performs manual setting, recording is made in proportion to the
input.
[0041]
FIG. 6B shows an example of the signal level of the digital audio signal input to the audio signal
processing unit 12. Usually, the signal level of the digital audio signal that can be processed by
the recording device 1 falls within the range of a predetermined threshold. In this example, the
upper limit of the signal level is indicated as the maximum input level. The signal level of the
digital audio signal input to the audio signal processing unit 12 without any processing may
exceed the maximum input level. Such digital audio signals cause distortion during sound
emission.
[0042]
FIG. 6C shows an example of the signal level of the digital audio signal when the recording mode
is set to the dictation mode or the conference mode. In this case, the signal level of the digital
audio signal is corrected almost uniformly. That is, small voices raise the signal level, and loud
voices lower the signal level. Then, the overall signal level is corrected not to exceed the
maximum input level.
[0043]
FIG. 6D shows an example of the signal level of the digital audio signal when the recording mode
is set to the music mode. In this case, the signal level of the digital audio signal is corrected by
narrowing the entire range while maintaining a certain degree of intonation. Because of this,
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small voices remain at low signal levels, and loud voices remain at high signal levels. Then, the
overall signal level is corrected not to exceed the maximum input level.
[0044]
FIG. 7 shows an example in which the signal level of the digital audio signal is adjusted to the
target level lower limit value. Target levels for keeping the signal level of the digital audio signal
within a predetermined range are defined as a target level lower limit value and a target level
upper limit value.
[0045]
When the signal level of the digital audio signal input to the audio signal processing unit 12
exceeds the determination threshold set for each recording mode, the output signal level is the
target level lower limit value and the target level using the following arithmetic expression It is
adjusted to be within the upper limit value. a0 = (target upper limit value-target lower limit value)
/ (maximum level-determination threshold value) equation (1) b0 = target upper limit value- (a0
× determination threshold value) equation (2) output signal level = ((a0 × reference standard)
Value + b0) ÷ reference value) × input signal level (3) On the other hand, for signals below the
determination threshold value, amplification of the signal is performed using the following
arithmetic expression. Output signal level = (target lower limit value / decision determination
threshold) × input signal level (4) However, when the signal level does not reach the
determination threshold set for each recording mode, the signal level correction process is not
performed.
[0046]
FIG. 8 shows an example in which the signal level of the digital audio signal is adjusted within the
range of the target level upper limit value and the lower limit value. The determination threshold
is set as in the case shown in FIG.
[0047]
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Here, it is assumed that the range of the signal level of the digital audio signal input to the audio
signal processing unit 12 exceeds the target level upper limit value or does not reach the target
level lower limit value. At this time, the fifth correction unit 25 limits and outputs the signal level
within the range from the target level lower limit value to the target level upper limit value.
[0048]
FIG. 9 shows an example in which the reference value is changed at a fixed attenuation amount
from the maximum value of the signal level of the digital audio signal input to the audio signal
processing unit 12.
[0049]
Here, the "reference value" will be described.
Reference values 42a, 42b, 45a to 45c are shown in FIG. The fifth correction unit 25 sets the
absolute value (peak 41a) of the digital audio signal of the maximum level input within a
predetermined period (one cycle in this example) as a reference value 42a. At this time, the fifth
correction unit 25 calculates how many times the signal level falls within the range of the target
level upper limit value and the lower limit value by multiplying the peak 41a (reference value
42a) by a multiple. Then, the fifth correction unit 25 calculates a parameter indicating how many
times the peak 41a (reference value 42a) is to be multiplied as a “magnification factor
parameter”.
[0050]
The fifth correction unit 25 corrects the signal level to be within the range of the target level
upper limit value and the lower limit value by multiplying the signal level of the input digital
audio signal by the “magnification factor”. In addition, the fifth correction unit 25 attenuates
the reference value 42 a regularly with the passage of time. The attenuation amount of the
reference value 42a is determined by the attenuation line 43 having a predetermined slope, with
the reference value 42a as a starting value.
[0051]
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Here, the peak 41b next to the peak 41a is examined. The peak 41 b is lower than the reference
value 42 a. For this reason, the fifth correction unit 25 applies the magnification parameter
obtained for the peak 41a as it is, and applies the correction to the signal level of the peak 41b.
Thus, the signal level of the peak 41b falls within the range of the target level upper limit value
and the lower limit value.
[0052]
When the audio signal of the maximum level exceeding the reference value 42b is input, the fifth
correction unit 25 sets the absolute value (peak 41c) of the signal level as the new reference
value 45a, and calculates the "magnification factor parameter". Then, the fifth correction unit 25
repeats the process of attenuating the reference value 45a with the lapse of time according to the
attenuation line 46.
[0053]
Thereafter, the signal level of the input digital audio signal and the reference value are compared
every cycle, and when the signal level is higher than the reference value, the process of resetting
the signal level based on the reference value is repeated.
[0054]
Thus, the reference value for adjusting the signal level is determined every predetermined period.
Then, the amount of attenuation per predetermined time of the reference value is constant as
shown by the attenuation lines 43 and 46. Therefore, for example, when one speaker speaks
loudly in a conference, the reference value is set high. After that, when another speaker speaks in
a small voice, the reference value is lowered. Thereby, the signal level can be appropriately
corrected within the range of the target level upper limit value and the lower limit value
regardless of the size of the speaker's voice.
[0055]
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FIG. 10 shows an example in which the amount of attenuation is changed according to the
maximum value of the signal level within a predetermined period. In quiet environments, the
signal level of digital audio signals is likely to be low. The fifth correction unit 25 performs
correction for raising the signal level to within the range of the target level upper limit value and
the lower limit value for a low signal level. Hereinafter, the time taken to adjust the correction
amount gradually following the state of the input signal and to raise the signal level of the digital
audio signal to within the range of the target level upper limit value and the lower limit value is
referred to as "recovery time". The recovery time, which will be described later, performed by the
fifth correction unit 25 changes in conjunction with the sensitivity of the microphones 2R and 2L
set in the recording mode.
[0056]
Conventionally, recovery has been constant regardless of the signal level. For this reason, when a
digital audio signal with a low signal level is input, the signal level remains low initially, and the
signal level is gradually raised. As a result, when the signal level suddenly changes from a proper
state to a low level, the voice recorded immediately after the change tends to be small, and the
contents of the statement become unclear. Therefore, the recording device 1 (fifth correction unit
25) of this example changes the recovery time according to the signal level of the input digital
audio signal. Specifically, the correction control unit 18 makes the attenuation amount of the
reference value per fixed time variable according to the level of the sound signal, and the sound
performed by the sound signal correction unit 16 (fifth correction unit 25) The speed at which
the signal level is corrected is made variable.
[0057]
As shown in FIG. 10, the fifth correction unit 25 calculates a parameter indicating how many
times the peak 51a (reference value 52a) is to be multiplied as a “magnification factor
parameter”. Then, the fifth correction unit 25 corrects the signal level to be within the range of
the target level upper limit value and the lower limit value by multiplying the signal level of the
input digital audio signal by the “magnification factor”. In addition, the fifth correction unit 25
attenuates the reference value 52a constantly as time passes. The attenuation amount of the
reference value 52a is determined by the attenuation line 53 having a predetermined slope, with
the reference value 52a as a starting value.
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[0058]
Here, the peaks 51b and 51c following the peak 51a will be examined. The peaks 51b and 51c
are smaller than the reference value 52a. For this reason, the fifth correction unit 25 applies the
reference value 52a as it is to obtain a magnification parameter, and multiplies the signal level of
the peaks 51b and 51c for correction. As a result, the signal levels of the peaks 51b and 51c fall
within the ranges of the target level upper limit value and the lower limit value.
[0059]
When the audio signal of the maximum level exceeding the reference value 52b is input, the fifth
correction unit 25 sets the absolute value (peak 51d) of the signal level as a new reference value
55a, and calculates the “magnification parameter”. Then, the fifth correction unit 25 repeats
the process of attenuating the reference value 55a to the reference values 55b and 55c with the
lapse of time according to the attenuation line 56.
[0060]
Thereafter, the signal level of the input digital audio signal and the reference value are compared
every predetermined period, and when the signal level is higher than the reference value, the
process of resetting the reference value based on the signal level is repeated.
[0061]
As shown in FIG. 10, when a voice with a small volume is input, the time required for recovery is
shortened.
On the other hand, when the volume is a loud voice, the time required for recovery is extended so
that the AGC can follow slowly. As a result, the signal level of the digital audio signal whose
volume is small quickly falls within the range of the target level upper limit value and the lower
limit value, so that the user suddenly changes the signal level from the appropriate state to the
low level. Even if it changes, you can hear clearly. In addition, when the signal level becomes
high, the time required for recovery becomes long. Therefore, the fifth correction unit 25 can
correct the signal level without frequently obtaining the magnification parameter.
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[0062]
According to the recording device 1 according to the embodiment described above, the user can
change the mode to the optimum recording mode and record the voice on the recording device 1
according to the scene to be recorded. At this time, the audio signal correction unit 16 is a filter
coefficient predetermined for each recording mode so that the correction filters of the first
correction unit 21 to the fourth correction unit 24 that correct the frequency characteristics of
the digital audio signal become optimal. Change automatically. Since the first correction unit 21
to the fourth correction unit 24 particularly correct the low frequency part of the frequency
characteristics of the microphones 2R and 2L, the frequency characteristic of the digital audio
signal to be recorded is high to low. It can be corrected flat to the area. In addition, when the low
range is corrected, noise may occur due to wind or the like being blown. In this case, it is possible
to control the low frequency by setting the recording mode not using the low frequency
correction filter, or setting the low frequency removal filter (LCF: Low Cut Filter) to turn
correction on or off. it can.
[0063]
In addition, the fifth correction unit 25 uses the frequency characteristics of the microphones 2R
and 2L according to the set recording mode, mainly for recording voices such as meetings and
dictations, and for recording musical instruments, natural sounds and the like. Then, the
microphones 2R and 2L are corrected to have an optimal frequency characteristic. At this time,
the parameters such as the filter coefficients of the microphones 2R and 2L, the AGC coefficient,
the attack time, the recovery time, etc. are set to combinations considered to be optimal
according to the respective applications, so that the recording state intended by the user is likely
to be achieved. effective.
[0064]
Further, even if the microphones 2R and 2L included in the recording device 1 are small, the
frequency characteristics of the collected audio signal can be flattened, so that it is possible to
record a digital audio signal with high sound quality. In addition, since the user can set the AGC
coefficient in accordance with the scene to be recorded by changing the recording mode, there is
an effect that it is possible to record natural speech.
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[0065]
<2. Modified Example> Although the recording apparatus 1 according to the above-described
embodiment corrects the frequency characteristics of the digital audio signal without changing
the microphones 2R and 2L and changes the reference value of the signal level, the microphones
2R and 2L Processing may be associated.
[0066]
FIG. 11 shows an example of comparing the signal level for each channel to change the signal
level. FIG. 11A shows an example of the signal level of the digital audio signal of the left channel
generated from the sound collected by the microphone 2L. FIG. 11B shows an example of the
signal level of the right channel digital audio signal generated from the sound collected by the
microphone 2R.
[0067]
In general, the microphones 2R and 2L built in the recording device 1 are arranged at a
predetermined distance (for example, about 2 cm), so that the strengths of the collected voices
are different, and as a result, digital audio signals of left and right channels are The signal levels
are also different. For this reason, the user who listens to the sound recorded by the recording
device 1 can obtain a sense of stereo. The recording device 1 of this example corrects the
frequency characteristics and signal level of the digital audio signal while maintaining the stereo
feeling.
[0068]
First, when audio signals of a plurality of channels (two channels in this example) are supplied,
the correction control unit 18 compares signal levels of digital audio signals of left and right
channels within a predetermined period for each channel. Next, the reference value 62a is set
from the peak 61 of the channel with high signal level (left channel shown in FIG. 11A). Then, the
fifth correction unit 25 repeats the process of attenuating the reference value 62a to the
reference values 62b and 62c with the lapse of time according to the attenuation line 63.
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[0069]
On the other hand, the maximum value (peak 64) of the signal level of the digital audio signal of
the channel having a low signal level (right channel shown in FIG. 11B) is the maximum signal
level of the digital audio signal at the same time as the signal level is high. This value is lower
than the value (peak 61) by ΔP. In this case, if the signal level of the right channel is corrected to
have the same height as the signal level of the left channel, the sense of stereo disappears despite
the stereo recording. Therefore, the signal level of the right channel is corrected in accordance
with the reference value (signal levels 62a, 62b, 62c) set by the signal level of the left channel.
[0070]
When there is a difference between the signal levels of the digital audio signals of the left and
right channels, the recording device 1 of this example applies the reference value set to the
channel with the high signal level also to the channel with the low signal level. At this time, when
audio signals of a plurality of channels are supplied, the correction control unit 18 compares the
levels of the audio signals within a predetermined period for each channel. Then, the correction
control unit 18 maintains the ratio of the level of the audio signal of another channel to the level
of the audio signal of the channel where the level of the audio signal is high, while maintaining
the ratio of the level of the audio signal of the other channel. Adjust the level. Thereby, the
balance of the signal levels of the left and right channels is maintained, and the stereo feeling of
the user is improved.
[0071]
Further, a recording medium having recorded thereon a program code of software for realizing
the functions of the first and second embodiments described above may be supplied to the
system or the apparatus. It goes without saying that the function is realized also when the
computer (or a control device such as a CPU or the like) of the system or apparatus reads out and
executes the program code stored in the recording medium.
[0072]
As a recording medium for supplying the program code in this case, for example, a floppy disk, a
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hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a nonvolatile memory card, a ROM, etc. may be used. Can.
[0073]
Further, the functions of the above-described embodiment are realized by executing the program
code read by the computer.
In addition, based on the instructions of the program code, an operating system (OS) or the like
running on the computer performs part or all of the actual processing. The case where the
function of the embodiment described above is realized by the process is also included.
[0074]
Further, the present invention is not limited to the above-described embodiment, and it goes
without saying that various other configurations can be taken without departing from the scope
of the present invention.
[0075]
DESCRIPTION OF SYMBOLS 1 ... Recording device, 2R, 2L ... Microphone, 3 ... Codec part, 4 ...
Main control part, 5 ... Recording part, 6 ... Power supply, 7 ... Operation part, 8 ... Display part, 9
... Speaker, 10 ... Earphone, 11 ... Recording medium, 12 ... Audio signal processing unit, 13 ...
Secondary control unit, 15 ... Preprocessing unit, 16 ... Audio signal correction unit, 17 ...
Selection unit, 18 ... Correction control unit, 21 ... First correction unit, 22 ... 2nd correction unit,
23 ... 3rd correction unit, 24 ... 4th correction unit, 25 ... 5th correction unit
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