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DESCRIPTION
ENCODING DEVICE, ENCODING METHOD, AND PROGRAM
TECHNICAL FIELD
5 [0001]
This technology relates to an encoding device, an
encoding method, and a program and especially relates to
the encoding device, the encoding method, and the program
capable of improving audio quality and more efficiently
10 encoding audio.
BACKGROUND ART
[0002]
Conventionally, HE-AAC (high efficiency MPEG
15 (moving picture experts group) 4 AAC (advanced audio
coding)) (ISO/IEC14496-3) is known as an encoding method
of an audio signal.
[0003]
In this encoding method, characteristic information
20 is extracted from a high-frequency signal component to be
encoded together with a low-frequency signal component
(refer to Patent Document 1, for example). At the time
of decoding, the low-frequency signal component is mapped
to a high-frequency range and a frequency envelope is
25 adjusted based on the information of the high-frequency
range included in a code string. In such encoding method,
only the characteristic information of the high-frequency
signal component is encoded as information regarding the
high-frequency signal component, so that it is possible
30 to improve coding efficiency while inhibiting
deterioration in audio quality.
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[0004]
In general, in the encoding device which adopts an
encoding system to encode only the characteristic
information of the high-frequency range as the
5 information regarding the high-frequency component, there
often is a case in which a code amount of the highfrequency
range is extremely smaller than that of a lowfrequency
range and adjusting flexibility of the code
amount of the high-frequency range is small. Therefore,
10 a method is such that the information regarding the highfrequency
signal component is first encoded and then the
low-frequency signal component is encoded with a
remaining code amount. Such a configuration may avoid a
complicated configuration of the encoding device and
15 prevent a large calculation amount.
CITATION LIST
PATENT DOCUMENT
[0005]
2 0 Patent Document 1: Japanese Patent Application Laid-Open
No. 2008-139844
SUMMARY OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION
25 [0006]
However, the above-described technology cannot
encode the audio fully efficiently while improving the
audio quality. Specifically, the code amount of the code
string of the low-frequency signal component and the code
30 amount of the characteristic information of the highfrequency
range cannot be appropriately controlled at the
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time of the encoding, for example.
[0007]
This technology is achieved in view of such a
situation and an object thereof is to improve the audio
5 quality and more efficiently encode the audio.
SOLUTIONS TO PROBLEMS
[0008]
An encoding device according to one aspect of this
10 technology includes a first high-frequency encoding unit
which calculates a high-frequency code amount being a
code amount of a high-frequency code string for obtaining
a high-frequency component based on a low-frequency
component and the high-frequency component of an input
15 signal, a low-frequency encoding unit which encodes the
low-frequency component of the input signal to generate a
low-frequency code string, a low-frequency decoding unit
which decodes the low-frequency code string, a second
high-frequency encoding unit which generates the high-
2 0 frequency code string based on a decoded low-frequency
component obtained by decoding the low-frequency code
string and the high-frequency component such that the
code amount of the high-frequency code string is not
larger than the high-frequency code amount, and a
25 multiplexing unit which multiplexes the low-frequency
code string and the high-frequency code string to
generate an output code string.
[0009]
It is possible to allow the first high-frequency
30 encoding unit to calculate the high-frequency code amount
based on low-frequency subband signals of a plurality of
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subbands composing the low-frequency component and highfrequency
subband signals of a plurality of subbands
composing the high-frequency component and allow the
second high-frequency encoding unit to generate the high-
5 frequency code string based on decoded low-frequency
subband signals of a plurality of subbands composing the
decoded low-frequency component and the high-frequency
subband signals.
[0010]
10 The encoding device may further include a delay
unit which delays the high-frequency code amount, the
decoded low-frequency component, and the high-frequency
component input to the second high-frequency encoding
unit.
15 [0011]
The encoding device may further include a code
amount adjusting unit which makes a difference between
the code amount of the high-frequency code string and the
high-frequency code amount a surplus code amount capable
20 of being used in subsequent processes and controls
storage of the surplus code amount, when the code amount
of the high-frequency code string obtained by the second
high-frequency encoding unit is smaller than the highfrequency
code amount.
25 [0012]
The surplus code amount may be used for adjusting
the code amount of at least any of the high-frequency
code string and the low-frequency code string.
[0013]
30 An encoding method or a program according to one
aspect of this technology includes the steps of
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calculating a high-frequency code amount being a code
amount of a high-frequency code string for obtaining a
high-frequency component based on a low-frequency
component and the high-frequency component of an input
5 signal, encoding the low-frequency component of the input
signal to generate a low-frequency code string, decoding
the low-frequency code string, generating the highfrequency
code string based on a decoded low-frequency
component obtained by decoding the low-frequency code
10 string, and'the high-frequency component such that the
code amount of the high-frequency code string is not
larger than the high-frequency code amount, and
multiplexing the low-frequency code string and the highfrequency
code string to generate an output code string.
15 [0014]
According to one aspect of this technology, the
high-frequency code amount being the code amount of the
high-frequency code string for obtaining the highfrequency
component is calculated based on the low-
20 frequency component and the high-frequency component of
the input signal, the low-frequency component of the
input signal is encoded and the low-frequency code string
is generated, the low-frequency code string is decoded,
the high-frequency code string is generated based on the
25 decoded low-frequency component obtained by decoding the
low-frequency code string and the high-frequency
component such that the code amount of the high-frequency
code string is not larger than the high-frequency code
amount, and the low-frequency code string and the high-
30 frequency code string are multiplexed to generate the
output code string.
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EFFECTS OF THE INVENTION
[0015]
According to one aspect of this technology, it is
5 possible to improve the audio quality and more
efficiently encode the audio.
BRIEF DESCRIPTION OF DRAWINGS
[0016]
10 Fig. 1 is a view illustrating.a configuration
example of one embodiment of an encoding device.
Fig. 2 is a view illustrating power of each subband
of an input signal.
Fig. 3 is a view illustrating the power of each
15 subband of the input signal and a decoded low-frequency
signal.
Fig. 4 is a flowchart illustrating an encoding
process.
Fig. 5 is a view illustrating a configuration
20 example of a decoding device.
Fig. 6 is a flowchart illustrating a decoding
process.
Fig. 7 is a view illustrating another configuration
example of the encoding device.
25 Fig. 8 is a view illustrating a configuration
example of a computer.
MODE FOR CARRYING OUT THE INVENTION
[0017]
30 Embodiments to which this technology is applied are
hereinafter described with reference to the drawings.
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[0018]

[Configuration Example of Encoding Device]
Fig. 1 is a view illustrating a configuration
5 example of one embodiment of an encoding device to which
this technology is applied.
[0019]
An encoding device 11 encodes an input signal being
an audio signal and outputs an output code string
10 obtained as a result.
[0020]
The encoding device 11 is composed of a subband
dividing circuit 21, a first high-frequency encoding
circuit 22, a low-pass filter 23, a low-frequency
15 encoding circuit 24, a low-frequency decoding circuit 25,
a subband dividing circuit 26, a delay circuit 27, a
delay circuit 28, a delay circuit 29, a second highfrequency
encoding circuit 30, a code amount adjusting
circuit 31, a code amount temporary storage circuit 32, a
20 delay circuit 33, and a multiplexing circuit 34.
[0021]
The subband dividing circuit 21 divides the input
signal into a plurality of subband signals, supplies an
obtained low-frequency subband signal to the first high-
25 frequency encoding circuit 22 and supplies a highfrequency
subband signal to the first high-frequency
encoding circuit 22 and the delay circuit 29.
[0022]
For example, a frequency band of an entire input
30 signal is divided into a plurality of frequency bands
having the same band width (hereinafter, referred to as
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subbands) and the input signal is divided into signals of
the subbands (hereinafter, referred to as the subband
signals). Out of the subband signals, the subband signal
of a predetermined subband on a high-frequency side is
5 made the high-frequency subband signal and the subband
signal of a predetermined subband on a low-frequency side
whose frequency is lower than that of the high-frequency
side is made the low-frequency subband signal.
[0023]
10 The first high-frequency encoding circuit 22
encodes an estimation coefficient used for estimating
power of the high-frequency subband signal based on a
feature amount obtained from the low-frequency subband
signal supplied from the subband dividing circuit 21 and
15 supplies a code amount (hereinafter, referred to as a
high-frequency code amount) to the low-frequency encoding
circuit 24 and the delay circuit 28.
[0024]
The low-pass filter 23 filters the input signal
2 0 supplied thereto and supplies a low-frequency signal
being a low-frequency component of the input signal
obtained as a result to the low-frequency encoding
circuit 24. The low-frequency signal is the signal
formed of the low-frequency subband signals on the low-
25 frequency side.
[0025]
The low-frequency encoding circuit 24 encodes the
low-frequency signal from the low-pass filter 23 with a
code amount obtained by subtracting the high-frequency
30 code amount supplied from the first high-frequency
encoding circuit 22 from a code amount available in a
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processing frame of the input signal. The low-frequency
encoding circuit 24 supplies a low-frequency code string
obtained by encoding the low-frequency signal to the lowfrequency
decoding circuit 25 and the delay circuit 33.
5 [0026]
The low-frequency decoding circuit 25 decodes the
low-frequency code string supplied from the low-frequency
encoding circuit 24 and supplies a decoded low-frequency
signal obtained as a result to the subband dividing
10 circuit 26. The subband dividing circuit 2 6 divides the
decoded low-frequency signal supplied from the lowfrequency
decoding circuit 25 into subband signals of a
plurality of subbands on the low-frequency side
(hereinafter, referred to as decoded low-frequency
15 subband signals) and supplies the same to the delay
circuit 27. Herein, frequency bands of the subbands of
the decoded low-frequency subband signals are the same as
those of the subbands of the low-frequency subband
signals.
20 [0027]
The delay circuit 27 delays the decoded lowfrequency
subband signal from the subband dividing
circuit 2 6 to supply to the second high-frequency
encoding circuit 30. The delay circuit 28 delays the
25 high-frequency code amount from the first high-frequency
encoding circuit 22 by a certain processing frame to
supply to the second high-frequency encoding circuit 30.
The delay circuit 2 9 delays the high-frequency subband
signal from the subband dividing circuit 21 to supply to
30 the second high-frequency encoding circuit 30.
[0028]
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The second high-frequency encoding circuit 30
encodes the estimation coefficient of the power of the
high-frequency subband signal from the delay circuit 2 9
such that the code amount is not larger than that
5 determined by the high-frequency code amount obtained by
the delay circuit 28 based on the feature amount obtained
from the decoded low-frequency subband signal output from
the delay circuit 27. The second high-frequency encoding
circuit 30 supplies a high-frequency code string obtained
10 by encoding the estimation coefficient to the
multiplexing circuit 34 and supplies the high-frequency
code amount of the high-frequency code string to the code
amount adjusting circuit 31.
[0029]
15 When the high-frequency code amount obtained by the
second high-frequency encoding circuit 30 is smaller than
the high-frequency code amount of the first highfrequency
encoding circuit 22 obtained through the delay
circuit 28, the code amount adjusting circuit 31 supplies
20 a surplus code amount to the code amount temporary
storage circuit 32. The code amount temporary storage
circuit 32 stores the surplus code amount. The surplus
code amount is appropriately used in subsequent
processing frames.
25 [0030]
The delay circuit 33 delays the low-frequency code
string obtained by the low-frequency encoding circuit 24
by a certain processing frame to supply to the
multiplexing circuit 34. The multiplexing circuit 34
30 multiplexes the low-frequency code string from the delay
circuit 33 and the high-frequency code string from the
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second high-frequency encoding circuit 30 and outputs the
output code string obtained as a result.
[0031]
[Improvement in Audio Quality]
5 In an encoding system in the encoding device 11 and
the encoding system such as HE-AAC, characteristic
information of a high-frequency component of the audio
signal is encoded with an extremely small code amount and
a large part of the code amount is assigned to a low-
10 frequency range being the frequency band in which
distortion is easily acoustically perceived by human.
The encoding device 11 actively adjusts the code amount
according to a state of the signal of the high-frequency
component, so that the high-frequency code amount often
15 varies significantly according to the processing frame.
[0032]
For such a reason, the above-described encoding'
system has a general configuration in which the highfrequency
signal is first encoded and then the low-
20 frequency signal is encoded with a remaining code amount.
[0033]
On the other hand, in an encoding method of
encoding the high-frequency component using the lowfrequency
component, the fact that the low-frequency
25 signal handled by the encoding device 11 and the lowfrequency
signal handled by a decoding device are
different from each other is a cause of deterioration in
audio quality of the high-frequency signal.
[0034]
30 That is to say, suppose that the input signal is
divided into the low-frequency subbands and the high12
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frequency subbands by subband division of the input
signal as illustrated in Fig. 2, for example. Meanwhile,
Fig. 2 illustrates power of each subband of the input
signal. In the drawing, a frequency is plotted along the
5 abscissa and the power of the subband signal of each
subband is plotted along the ordinate.
[0035]
In an example in Fig. 2, the low-frequency
component of the input signal is divided into 4 subbands
10 which are subbands sb-3 to sb, and the high-frequency
component of the input signal is divided into 12 subbands
which are subbands sb+1 to sb+12. The subband adjacent
to a high-frequency side of the subband sb whose
frequency is the highest on the low-frequency side is
15 made the subband sb+1 whose frequency is the lowest on
the high-frequency side.
[0036]
Herein, in the drawing of each subband, a solid
line in a transverse direction indicates the power of the
2 0 subband signal (low-frequency subband signal or highfrequency
subband signal) of the subband.
[0037]
Suppose that the low-frequency component of such
input signal is encoded and the low-frequency code string
25 obtained by the encoding is decoded by the decoding
device. In this case, when the subband division of the
decoded low-frequency signal obtained by decoding the
low-frequency code string is performed, the decoded lowfrequency
signal is divided into four subbands which are
30 the subbands sb-3 to sb, as illustrated in Fig. 3, for
example.
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[0038]
Meanwhile, in Fig. 3, the frequency is plotted
along the abscissa and the power of the subband signal of
each subband is plotted along the ordinate. Also, the
5 solid line in the transverse direction of each subband
indicates the power of each subband signal before the
encoding of the input signal and a dashed-dotted line in
the transverse direction of each subband indicates the
power of the decoded low-frequency subband signal forming
10 the decoded low-frequency signal obtained by the decoding
device.
[0039]
As illustrated in Fig. 3, the decoded low-frequency
signal obtained by the decoding device includes an
15 encoding error, so that, the power of the decoded lowfrequency
subband signal is different from the power of
the low-frequency subband signal in the encoding device
11 as a result.
[0040]
20 Therefore, when the estimation coefficient with
which it is possible to estimate the power of the highfrequency
subband signal with the highest degree of
accuracy is selected from a plurality of estimation
coefficients from the feature amount and the high-
25 frequency subband signal using the power of the lowfrequency
subband signal as the feature amount, for
example, and this is output to the decoding device, the
audio quality might be deteriorated.
[0041]
30 That is to say, on the encoding side, the power of
the high-frequency subband signal is estimated using the
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low-frequency subband signal different from the decoded
low-frequency subband signal obtained by the decoding
device, the high-frequency subband signal, and the
estimation coefficient and the most appropriate
5 estimation coefficient is selected from an estimated
result. Therefore, when the estimation coefficient
selected in this manner is used, it is not always
possible to estimate the power of the high-frequency
subband signal with a high degree of accuracy if the low-
10 frequency component used for estimating the power of the
high-frequency subband signal is different between the
encoding side and the decoding side.
[0042]
Therefore, in order to improve the audio quality by
15 performing more accurate estimation, it is necessary that
the decoding device which decodes the low-frequency code
string is embedded also in the encoding device and that a
high-frequency range is encoded using the decoded lowfrequency
signal obtained thereby.
20 [0043]
The encoding device 11 is provided with the lowfrequency
decoding circuit 25 which decodes the lowfrequency
code string, and this encodes the highfrequency
range using the decoded low-frequency subband
25 signal obtained by the low-frequency decoding circuit 25,
so that it is possible to improve the quality of the
audio obtained by the decoding.
[0044]
[Description of Encoding Process]
30 Next, operation of the encoding device 11 is
described. When the encoding device 11 is supplied with
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the input signal and instructed to encode the input
signal, the encoding device 11 performs an encoding
process to encode the input signal. The encoding process
by the encoding device 11 is hereinafter described with
5 reference to a flowchart in Fig. 4.
[0045]
At step Sll, the subband dividing circuit 21
equally divides the supplied input signal into a
plurality of subband signals having a predetermined
10 bandwidth. The subband signals in. a specific range on
the low-frequency side out of the subband signals herein
obtained are made the low-frequency subband signals and
the subband signals in a specific range on the highfrequency
side are made the high-frequency subband'
15 signals.
[0046]
The subband dividing circuit 21 supplies the lowfrequency
subband signal obtained by the subband division
to the first high-frequency encoding circuit 22 and
20 supplies the high-frequency subband signal to the first
high-frequency encoding circuit 22 and the delay circuit
29.
[0047]
For example, the range of the subbands of the high-
25 frequency subband signals is set on the encoding device
11 side according to a property, a bit rate and the like
of the input signal. Also, the range of the subbands of
the low-frequency subband signals is the frequency band
having a certain number of subbands in which the subband
30 on a lower-frequency side by one than the lowestfrequency
subband of the high-frequency subband signal is
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the highest-frequency subband of the low-frequency
subband signal. In this manner, the range of the
subbands covered by the low-frequency subband signals and
the high-frequency subband signals is the same in the
5 encoding device 11 and the decoding device.
[0048]
At step S12, the first high-frequency encoding
circuit 22 encodes the high-frequency range based on
estimation from the low-frequency subband signal supplied
10 from the subband dividing circuit 21 to calculate the
high-frequency code amount and supplies the highfrequency
code amount to the low-frequency encoding
circuit 24 and the delay circuit 28.
[0049]
15 For example, the first high-frequency encoding
circuit 22 calculates the power of the low-frequency
subband signal (hereinafter, referred to as low-frequency
subband power) of each subband supplied from the subband
dividing circuit 21 as the feature amount. The first
20 high-frequency encoding circuit 22 also calculates an
estimate value of the power of the high-frequency subband
signal of each high-frequency subband (hereinafter,
referred to as pseudo high-frequency subband power) from
the low-frequency subband power and the estimation
25 coefficient for each of a plurality of estimation
coefficients. Specifically, the low-frequency subband
power of each of the subbands are linearly combined using
the estimation coefficient for each subband and the
pseudo high-frequency subband power of a predetermined
30 subband is obtained.
[0050]
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Then, the first high-frequency encoding circuit 22
compares the pseudo high-frequency subband power to
actual power of the high-frequency subband signal
(hereinafter, referred to as high-frequency subband
5 power) and selects the estimation coefficient with which
the high-frequency range of the input signal may be
estimated with the highest degree of accuracy out of a
plurality of estimation coefficients. The first highfrequency
encoding circuit 22 makes a code amount of a
10 coefficient index which specifies the selected estimation
coefficient, the code amount of the encoded highfrequency
component, that is to say, the high-frequency
code amount.
[0051]
15 Meanwhile, various encoding methods may be used as
long as they are the encoding methods of encoding the
high-frequency range by using the low-frequency signal.
Also, in a high-frequency encoding process at step S12,
the encoding is not necessarily actually performed if the
20 high-frequency code amount may be calculated. Further,
when it is wanted to reduce a calculation processing
amount, a configuration in which a part of the process is
omitted and an estimate value of the high-frequency code
amount is obtained is also possible.
25 [0052]
At step S13, the low-pass filter 23 performs a
filtering process of the supplied input signal, thereby
allowing a low-frequency component of the input signal to
pass to generate the low-frequency signal and outputs the
30 same to the low-frequency encoding circuit 24. Although
an optional frequency may be set as a cutoff frequency of
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the filter used in the filtering process, in this
embodiment, the cutoff frequency is set corresponding to
an upper-end frequency of the above-described lowfrequency
subband signal.
5 [0053]
At step S14, the low-frequency encoding circuit 24
encodes the low-frequency signal from the low-pass filter
23 with the code amount obtained by subtracting the highfrequency
code amount supplied from the first high-
10 frequency encoding circuit 22 from the code amount
available in an entire processing frame determined in
advance. The low-frequency encoding circuit 24 outputs
the low-frequency code string obtained by the encoding of
the low-frequency signal to the low-frequency decoding
15 circuit 25 and the delay circuit 33.
[0054]
At step S15, the low-frequency decoding circuit 25
decodes the low-frequency code string supplied from the
low-frequency encoding circuit 24 and outputs the decoded
20 low-frequency signal thereby obtained to the subband
dividing circuit 26. Meanwhile, the encoding device 11
may use various encoding systems for encoding and
decoding the low-frequency signal and it is possible to
adopt ACELP (algebraic code excited linear prediction),
25 AAC (advanced audio coding) and the like, for example.
[0055]
At step S16, the subband dividing circuit 2 6
divides the decoded low-frequency signal supplied from
the low-frequency decoding circuit 25 into the decoded
30 low-frequency subband signals of a plurality of subbands
and outputs the same to the delay circuit 27. Lower-end
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and upper-end frequencies of each subband in this subband
division are identical to those of the subband division
performed by the subband dividing circuit 21 at step Sll.
That is to say, the frequency bands of the subbands of
5 the decoded low-frequency subband signals are the same as
those of the subbands of the low-frequency subband
signals.
[0056]
At step S17, the delay circuit 27 delays the
10 decoded low-frequency subband signal supplied from the
subband dividing circuit 2 6 by a specific time sample to
supply to the second high-frequency encoding circuit 30.
[0057]
A delay amount in the delay circuit 27 is set for
15 synchronization of the low-frequency signal, the highfrequency
signal, the high-frequency code amount, and the
low-frequency code string, and it is required to set an
appropriate value according to the encoding system of the
low-frequency range and the high-frequency range. Of
20 course, there might be a case in which the delay amount
of each delay circuit is set to 0 according to the
configuration of the encoding system. Other delay
circuits 28, 29 and 33 have a function equivalent to that
of the delay circuit 27, so that the description thereof
25 is herein omitted.
[0058]
At step S18, the second high-frequency encoding
circuit 30 encodes the estimation coefficient of the
power of the high-frequency subband signal supplied from
30 the delay circuit 2 9 based on the feature amount obtained
from the decoded low-frequency subband signal output from
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the delay circuit 27 such that the code amount is not
larger than the high-frequency code amount supplied from
the delay circuit 28.
[0059]
5 For example, the second high-frequency encoding
circuit 30 adds the surplus code amount stored in the
code amount temporary storage circuit 32 to the highfrequency
code amount supplied from the delay circuit 2 8
to calculate a high-frequency code amount which is
10 corrected (hereinafter referred to as a corrected highfrequency
code amount). At that time, when the surplus
code amount is not smaller than an upper-limit correction
amount determined in advance of the high-frequency code
amount, a code amount obtained by adding the upper-limit
15 correction amount to the high-frequency code amount is
made the corrected high-frequency code amount.
[0060]
When the high-frequency code amount is corrected,
the code amount adjusting circuit 31 supplies information
2 0 indicating the surplus code amount or the upper-limit
correction amount to the second high-frequency encoding
circuit 30 based on the surplus code amount stored in the
code amount temporary storage circuit 32. The code
amount adjusting circuit 31 also updates the surplus code
25 amount of the code amount temporary storage circuit 32.
For example, when the information indicating the upperlimit
correction amount is supplied to the second highfrequency
encoding circuit 30, the code amount adjusting
circuit 31 makes a code amount obtained by subtracting
30 the upper-limit correction amount from the surplus code
amount an updated surplus code amount.
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[0061]
Further, the second high-frequency encoding circuit
30 encodes the high-frequency component of the audio
signal of the frame to be processed based on the high-
5 frequency subband signal and the decoded low-frequency
subband signal such that the code amount of the highfrequency
code string is not larger than the corrected
high-frequency code amount.
[0062]
10 For example, the second high-frequency encoding
circuit 30 divides the frame to be processed into several
sections and performs the process similar to the process
at step S12, thereby selecting the estimation coefficient
of each section.
15 [0063]
That is to say, the second high-frequency encoding
circuit 30 obtains the decoded low-frequency subband
power from the decoded low-frequency subband signal and
calculates the pseudo high-frequency subband power from
20 the decoded low-frequency subband power and the
estimation coefficient for each estimation coefficient.
Then, the second high-frequency encoding circuit 30
compares the pseudo high-frequency subband power to the
high-frequency subband power of the high-frequency
25 subband signal and selects the estimation coefficient
with which the high-frequency range of the input signal
may be estimated with the highest degree of accuracy.
The second high-frequency encoding circuit 30 makes a
code string formed of the coefficient index indicating
30 the estimation coefficient of each section composing the
frame to be processed the high-frequency code string.
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[0064]
Herein, the code amount of the high-frequency code
string is adjusted by changing the number of sections
composing the frame to be processed, for example. When
5 the same estimation coefficient is selected in continuous
sections, it is also possible to adjust the code amount
of the high-frequency code string by making information
formed of information to specify the sections and the
coefficient index of selected one estimation coefficient
10 the code string composing the high-frequency code string.
[0065]
Meanwhile, it is also possible that the highfrequency
code amount is not corrected. In such a case,
the high-frequency range is encoded such that the code
15 amount of the high-frequency code string is not larger
than the high-frequency code amount output from the delay
circuit 28.
[0066]
In the encoding system at step S18, as in the
20 encoding system of the process at step S12, various
encoding methods may be used as long as they are the
encoding methods of encoding the high-frequency range
using the low-frequency signal; however, it is required
that this is at least based on the same encoding standard
25 as that of the encoding system at step S12. The encoding
process at step S18 is clearly different from the
encoding process at step S12 in that, first, it is
required to encode such that the code amount is not
larger than the high-frequency code amount calculated at
30 step S12, and second, the low-frequency signal required
for encoding the high-frequency range is the decoded low23
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frequency signal (decoded low-frequency subband signal).
[0067]
In this manner, by provisionally encoding the highfrequency
range by the first high-frequency encoding
5 circuit 22 to determine the high-frequency code amount
and actually encoding the high-frequency range such that
the code amount of the high-frequency code string is not
larger than the code amount determined by the highfrequency
code amount, it is possible to fix the code
10 amount of the high-frequency code string before the
encoding of the high-frequency range is performed.
According to this, it is possible to obtain the code
amount assigned to the low-frequency code string, so that
it is possible immediately encode the low-frequency
15 signal and more efficiently encode the input signal.
[0068]
At step S19, the second high-frequency encoding
circuit 30 determines whether the code amount of the
high-frequency code string obtained by the encoding is
20 smaller than the corrected high-frequency code amount.
[0069]
At step S19, when it is determined that the code
amount is not smaller than the corrected high-frequency
code amount, that is to say, when the code amount of the
25 high-frequency code string conforms to the corrected
high-frequency code amount, the surplus code is not
generated, so that the process shifts to step S23. At
that time, the second high-frequency encoding circuit 30
supplies the high-frequency code string obtained by
30 encoding the high-frequency range to the multiplexing
circuit 34.
24
SP328830WO00
[0070]
On the other hand, when it is determined that the
code amount is smaller than the corrected high-frequency
code amount at step S19, the code amount adjusting
5 circuit 31 stores a difference between the code amount of
the high-frequency code string and the corrected highfrequency
code amount in the code amount temporary
storage circuit 32 at step S20. That is to say, the code
amount being the difference between the code amount of
10 the high-frequency code string and the corrected highfrequency
code amount is added to the surplus code amount
stored in the code amount temporary storage circuit 32
and the surplus code amount is updated.
[0071]
15 Such code amount temporary storage circuit 32 is
also used in the AAC under the name of a bit resolver for
adjusting the code amount between the processing frames.
Meanwhile, although the encoding device 11 is configured
such that the surplus code amount is used for the high-
20 frequency encoding, this may also be commonly used when
there is a circuit having the similar function in the
encoding system of the low-frequency signal. That is to
say, the surplus code amount may be used only for
adjusting the code amount of any one of the high-
25 frequency code string and the low-frequency code string
or may be used for adjusting the code amount of both of
them.
[0072]
At step S21, the code amount adjusting circuit 31
30 determines whether the surplus code amount stored in the
code amount temporary storage circuit 32 reaches an upper
25
SP328830WO00
limit determined in advance.
[0073]
For example, in the code amount temporary storage
circuit 32, an upper limit of the code amount which may
5 be made the surplus code amount (hereinafter, referred to
as an upper-limit code amount) is determined in advance.
The code amount adjusting circuit 31 determines that the
surplus code amount reaches the upper limit at step S21
when the surplus code amount reaches the upper-limit code
10 amount at the time of.the storage of the difference
between the code amount of the high-frequency code string
and the corrected high-frequency code amount in the code
amount temporary storage circuit 32 started at step S20.
[0074]
15 At step S21, when it is determined that the surplus
code amount does not reach the upper limit, an entire
difference between the code amount of the high-frequency
code string and the corrected high-frequency code amount
is added to the surplus code amount and the surplus code
20 amount is updated. Thereafter, the second high-frequency
encoding circuit 30 supplies the high-frequency code
string obtained by encoding the high-frequency range to
the multiplexing circuit 34 and the process shifts to
step S23.
25 [0075]
On the other hand, when it is determined that the
surplus code amount reaches the upper limit at step S21,
the second high-frequency encoding circuit 30 performs
zero padding to the high-frequency code string at step
30 S22.
[0076]
26
SP328830WO00
While the difference between the code amount of the
high-frequency code string and the corrected highfrequency
code amount is added to the surplus code amount,
when the surplus code amount reaches the upper-limit code
5 amount, an unprocessed code amount, which is not yet
added to the surplus code amount, out of the difference
between the code amount of the high-frequency code string
and the corrected high-frequency code amount remains.
The unprocessed code amount cannot be added to the
10 surplus code amount, so that the second high-frequency
encoding circuit 30 adds a code "0" at the end of the
high-frequency code string by an amount of the
unprocessed code amount such that the unprocessed code
amount is apparently used for generating the high-
15 frequency code string. Meanwhile, at the time of
decoding, the code "0" added at the end of the highfrequency
code string is not used for decoding the input
signal.
[0077]
20 When the second high-frequency encoding circuit 30
performs the zero padding to add the code "0" at the end
of the high-frequency code string, this supplies the
high-frequency code string after the zero padding to the
multiplexing circuit 34 and the process shifts to step
25 S23.
[0078]
When it is determined that the code amount is not
smaller than the corrected high-frequency code amount at
step S19, when it is determined that the surplus code
30 amount does not reach the upper limit at step S21, or
when the zero padding is performed at step S22, the
27
SP328830WO00
process at step S23 is performed.
[0079]
That is to say, at step S23, the multiplexing
circuit 34 multiplexes the low-frequency code string from
5 the delay circuit 33 and the high-frequency code string
from the second high-frequency encoding circuit 30 to
generate the output code string and outputs the output
code string. At that time, the multiplexing circuit 34
also multiplexes indexes indicating upper-end and lower-
10 end subbands on the low-frequency side of the input
signal together with the low-frequency code string and
the high-frequency code string. When the output code
string is output in this manner, the encoding process is
finished.
15 [0080]
As described above, the encoding device 11 obtains
the high-frequency code amount to encode the lowfrequency
signal with the code amount determined by the
high-frequency code amount and encodes the high-frequency
20 component based on the decoded low-frequency signal
obtained by decoding the low-frequency code string and
the high-frequency code amount.
[0081]
In this manner, by provisionally encoding the high-
25 frequency range to determine the high-frequency code
amount and actually encoding the high-frequency range
such that the code amount of the high-frequency code
string is not larger than the code amount determined by
the high-frequency code amount, it is possible to fix the
30 code amount of the high-frequency code string before the
high-frequency range is encoded. According to this, it
28
SP328830WO00
is possible to obtain the code amount assigned to the
low-frequency code string and immediately encode the lowfrequency
signal. Therefore, it is possible to
efficiently encode so as to avoid a complicated
5 configuration of the encoding device 11 and avoid
increase in calculation amount. It is also possible to
select a more appropriate estimation coefficient by
encoding the high-frequency range using the decoded lowfrequency
signal, thereby improving the quality of the
10 audio.
[0082]
[Configuration Example of Decoding Device]
Next, the decoding device to which the output code
string output from the encoding device 11 is input as the
15 input code string, the decoding device which decodes the
input code string is described. The decoding device is
configured as illustrated in Fig. 5, for example.
[0083]
A decoding device 61 is composed of a
20 demultiplexing circuit 71, a low-frequency decoding
circuit 72, a subband dividing circuit 73, a feature
amount calculating circuit 74, a high-frequency decoding
circuit 75, a decoded high-frequency subband power
calculating circuit 76, a decoded high-frequency signal
25 generating circuit 77, and a synthesizing circuit 78.
[0084]
The demultiplexing circuit 71 demultiplexes the
input code string into the high-frequency code string and
the low-frequency code string and supplies the low-
30 frequency code string and the high-frequency code string
to the low-frequency decoding circuit 72 and the high29
SP328830WO00
frequency decoding circuit 75, respectively.
[0085]
The low-frequency decoding circuit 72 decodes the
low-frequency code string from the demultiplexing circuit
5 71 and supplies the decoded low-frequency signal obtained
as a result to the subband dividing circuit 73 and the
synthesizing circuit 78.
[0086]
The subband dividing circuit 73 equally divides the
10 decoded low-frequency signal from the low-frequency
decoding circuit 72 into a plurality of subband signals
having a predetermined band width and supplies the
obtained subband signal (decoded low-frequency subband
signal) to the feature amount calculating circuit 74 and
15 the decoded high-frequency signal generating circuit 77.
[0087]
The feature amount calculating circuit 74
calculates the feature amount using the decoded lowfrequency
subband signal from the subband dividing
20 circuit 73 and supplies the same to the decoded highfrequency
subband power calculating circuit 76.
[0088]
The high-frequency decoding circuit 75 which
associates the coefficient index and the estimation
25 coefficient with each other to record, decodes the highfrequency
code string from the demultiplexing circuit 71
and supplies the estimation coefficient specified by the
coefficient index obtained as a result to the decoded
high-frequency subband power calculating circuit 76.
30 [0089]
The decoded high-frequency subband power
30
SP328830WO00
calculating circuit 7 6 calculates decoded high-frequency
subband power being an estimate value of the highfrequency
subband power of each subband on the highfrequency
side of the input signal based on the feature
5 amount from the feature amount calculating circuit 74 and
the estimation coefficient from the high-frequency
decoding circuit 75 and supplies the same to the decoded
high-frequency signal generating circuit 77.
[0090]
10 The decoded high-frequency signal generating
circuit 77 generates a decoded high-frequency signal
based on the decoded low-frequency subband signal from
the subband dividing circuit 73 and the decoded highfrequency
subband power from the decoded high-frequency
15 subband power calculating circuit 7 6 and supplies the
same to the synthesizing circuit 78. The synthesizing
circuit 7 8 synthesizes the decoded low-frequency signal
from the low-frequency decoding circuit 72 and the
decoded high-frequency signal from the decoded high-
2 0 frequency signal generating circuit 77 and outputs the
same as an output signal.
[0091]
[Description of Decoding Process]
Next, operation of the decoding device 61 is
25 described. When the output code string is supplied from
the encoding device 11, the decoding device 61 makes the
output code string the input code string and performs a
decoding process thereof to output the output signal.
Hereinafter, the decoding process by the decoding device
30 61 is described with reference to a flowchart in Fig. 6.
[0092]
31
SP328830WO00
At step S51, the demultiplexing circuit 71
demultiplexes the input code string into the highfrequency
code string and the low-frequency code string
and supplies the low-frequency code string and the high-
5 frequency code string to the low-frequency decoding
circuit 72 and the high-frequency decoding circuit 75,
respectively. At that time, the demultiplexing circuit
71 supplies the indexes indicating the upper-end and
lower-end subbands on the low-frequency side of the input
10 signal obtained by demultiplexing as needed to the
subband dividing circuit 73 through the low-frequency
decoding circuit 72. According to this, the subband
dividing circuit 73 may specify the frequency band
suitable for each low-frequency subband.
15 [0093]
At step S52, the low-frequency decoding circuit 72
decodes the low-frequency code string from the
demultiplexing circuit 71 and supplies the decoded lowfrequency
signal obtained as a result to the subband
20 dividing circuit 73 and the synthesizing circuit 78.
[0094]
At step S53, the subband dividing circuit 73
divides the decoded low-frequency signal from the lowfrequency
decoding circuit 72 into a plurality of decoded
25 low-frequency subband signals using the index from the
demultiplexing circuit 71 as needed and supplies the same
to the feature amount calculating circuit 74 and the
decoded high-frequency signal generating circuit 77.
[0095]
30 At step S54, the feature amount calculating circuit
74 calculates the feature amount using the decoded low32
SP328830WO00
frequency subband signal from the subband dividing
circuit 73 and supplies the same to the decoded highfrequency
subband power calculating circuit 76. For
example, the decoded low-frequency subband power being
5 the power of the decoded low-frequency subband signal of
each subband is calculated as the feature amount.
[0096]
At step S55, the high-frequency decoding circuit 75
decodes the high-frequency code string from the
10 demultiplexing circuit 71 and outputs the estimation
coefficient specified by the coefficient index obtained
as a result to the decoded high-frequency subband power
calculating circuit 76.
[0097]
15 At step S56, the decoded high-frequency subband
power calculating circuit 7 6 calculates the decoded highfrequency
subband power of each high-frequency subband
based on the feature amount from the feature amount
calculating circuit 14 and the estimation coefficient
20 from the high-frequency decoding circuit 75 and supplies
the same to the decoded high-frequency signal generating
circuit 77.
[0098]
For example, the decoded low-frequency subband
25 power of each of the subbands as the feature amounts are
linearly combined using the estimation coefficient for
each subband to obtain the decoded high-frequency subband
power of a predetermined subband.
[0099]
30 At step S57, the decoded high-frequency signal
generating circuit 77 generates the decoded high33
SP328830WO00
frequency signal based on the decoded low-frequency
subband signal from the subband dividing circuit 73 and
the decoded high-frequency subband power from the decoded
high-frequency subband power calculating circuit 7 6 and
5 supplies the same to the synthesizing circuit 78.
[0100]
At step S58, the synthesizing circuit 78
synthesizes the decoded low-frequency signal from the
low-frequency decoding circuit 72 and the decoded high-
10 frequency signal from the decoded high-frequency signal
generating circuit 77 and outputs the same as the output
signal. The output signal is the audio signal formed of
the high-frequency component predicted using the
estimation coefficient and the low-frequency component
15 obtained by the decoding.
[0101]
When the output signal is generated to be output,
the decoding process is finished. The decoding device 61
demultiplexes the input code string in this manner,
20 estimates the high-frequency component using the
estimation coefficient obtained from the high-frequency
code string, and generates the output signal. By
estimating the high-frequency component using the
estimation coefficient in this manner, it is possible to
25 more efficiently decode and improve the quality of the
audio obtained by the decoding.
[0102]
(Variation)
[Configuration Example of Encoding Device]
30 Meanwhile, although the case in which various
signals and pieces of information such as the high34
SP328830WO00
frequency code amount and the high-frequency subband
signal are delayed as needed in the encoding device 11 is
described above, when it is not necessarily required to
delay, a configuration in which an encoding device is not
5 provided with a delay circuit is also possible.
[0103]
In such a case, the encoding device is configured
as illustrated in Fig. 7, for example. Meanwhile, in Fig.
7, the same reference sign is assigned to a part
10 corresponding to that in Fig. 1 and description thereof
is appropriately omitted.
[0104]
An encoding device 111 in Fig. 7 is composed of a
high-pass filter 121, a first high-frequency encoding
15 circuit 22, a low-pass filter 23, a low-frequency
encoding circuit 24, a low-frequency decoding circuit 25,
a second high-frequency encoding circuit 30, and a
multiplexing circuit 34.
[0105]
20 The high-pass filter 121 performs a filtering
process of a supplied input signal to extract a highfrequency
signal being a high-frequency component from
the input signal and supplies the same to the first highfrequency
encoding circuit 22 and the second high-
25 frequency encoding circuit 30. The low-pass filter 23
performs the filtering process of the supplied input
signal to extract a low-frequency signal being a lowfrequency
component from the input signal and supplies
the same to the first high-frequency encoding circuit 22
30 and the low-frequency encoding circuit 24.
[0106]
35
SP328830WO00
The first high-frequency encoding circuit 22
encodes a high-frequency range of the input signal based
on the high-frequency signal from the high-pass filter
121 and the low-frequency signal from the low-pass filter
5 23 and supplies a high-frequency code amount thereby
obtained to the low-frequency encoding circuit 24 and the
second high-frequency encoding circuit 30.
[0107]
The low-frequency encoding circuit 24 encodes the
10 low-frequency signal from the low-pass filter 23 with a
code amount obtained by subtracting the high-frequency
code amount from the first high-frequency encoding
circuit 22 from a code amount available in an entire
processing frame and supplies a low-frequency code string
15 thereby obtained to the low-frequency decoding circuit 25
and the multiplexing circuit 34. The low-frequency
decoding circuit 25 decodes the low-frequency code string
from the low-frequency encoding circuit 2 4 and supplies a
decoded low-frequency signal obtained as a result to the
20 second high-frequency encoding circuit 30.
[0108]
The second high-frequency encoding circuit 30
encodes the high-frequency component of the input signal
based on the high-frequency signal from the high-pass
25 filter 121 and the decoded low-frequency signal from the
low-frequency decoding circuit 25 such that the code
amount is not larger than the code amount determined by
the high-frequency code amount from the first highfrequency
encoding circuit 22. The second high-frequency
30 encoding circuit 30 supplies the high-frequency code
string obtained by the encoding of the high-frequency
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SP328830WO00
range to the multiplexing circuit 34. The multiplexing
circuit 34 multiplexes the low-frequency code string from
the low-frequency encoding circuit 24 and the highfrequency
code string from the second high-frequency
5 encoding circuit 30 and outputs the output code string
obtained as a result.
[0109]
The above-described series of processes may be
executed by hardware or may be executed by software.
10 When a series of processes is executed by the software, a
program which composes the software, is installed from a
program recording medium on a computer embedded in
dedicated hardware or a general-purpose personal computer,
for example, capable of executing various functions with
15 various programs installed.
[0110]
Fig. 8 is a block diagram illustrating a
configuration example of the hardware of the computer
which executes the above-described series of processes by
2 0 the program.
[0111]
In this computer, a CPU (central processing unit)
501, a ROM (read only memory) 502, and a RAM (random
access memory) 503 are connected to one another through a
25 bus 504.
[0112]
An input/output interface 505 is further connected
to the bus 504. An input unit 506 composed of a keyboard,
a mouse, a microphone and the like, an output unit 507
30 composed of a display, a speaker and the like, a
recording unit 508 composed of a hard disk, a nonvolatile
37
SP328830WO00
memory and the like, a communicating unit 509 composed of
a network interface and the like, and a drive 510 which
drives a removable medium 511 such as a magnetic disk, an
optical disk, a magnetooptical disk, or a semiconductor
5 memory are connected to the input/output interface 505.
[0113]
In the computer configured as described above, the
CPU 501 loads the program recorded in the recording unit
508, for example, on the RAM 503 through the input/output
10 interface 505 and.the bus 504 to execute, for example,
and according to this, the above-described series of
processes is performed.
[0114]
The program executed by the computer (CPU 501) is
15 provided in a state of being recorded on the removable
medium 511 which is a packaged medium formed of the
magnetic disk (including a flexible disk), the optical
disk (CD-ROM (compact disc-read only memory), a DVD
(digital versatile disc) and the like), the
20 magnetooptical disk, or the semiconductor memory, for
example, or through a wired or wireless transmission
medium such as a local area network, the Internet, and
digital satellite broadcasting.
[0115]
25 The program may be installed on the recording unit
508 through the input/output interface 505 by mounting of
the removable medium 511 on the drive 510. Also, the
program may be received by the communicating unit 509
through the wired or wireless transmission medium to be
30 installed on the recording unit 508. In addition, the
program may be installed in advance on the ROM 502 and
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SP328830WO00
the recording unit 508.
[0116]
Meanwhile, the program executed by the computer may
be the program whose process is performed in
5 chronological order in the order described in this
specification or may be the program whose process is
performed in parallel or at required timing such as when
there is a call.
[0117]
0 The embodiment of this technology, is not limited to
the above-described embodiment and various modifications
may be made without departing from the scope of this
technology.
5 REFERENCE SIGNS LIST
[0118]
11 encoding device, 22 first high-frequency
encoding circuit, 24 low-frequency encoding circuit, 25
low-frequency decoding circuit, 30 second high-frequency
0 encoding circuit, 31 code amount adjusting circuit, 32
code amount temporary storage circuit, 34 multiplexing
circuit

39
SP328830WO00
CLAIMS
1. An encoding device, comprising
a first high-frequency encoding unit which
5 calculates a high-frequency code amount being a code
amount of a high-frequency code string for obtaining a
high-frequency component based on a low-frequency
component and the high-frequency component of an input
signal;
10 a low-frequency encoding unit which encodes the
low-frequency component of the input signal to generate a
low-frequency code string;
a low-frequency decoding unit which decodes the
low-frequency code string;
15 a second high-frequency encoding unit which
generates the high-frequency code string based on a
decoded low-frequency component obtained by decoding the
low-frequency code string and the high-frequency
component such that the code amount of the high-frequency
20 code string is not larger than the high-frequency code
amount; and
a multiplexing unit which multiplexes the lowfrequency
code string and the high-frequency code string
to generate an output code string.
25
2. The encoding device according to claim 1, wherein
the first high-frequency encoding unit calculates
the high-frequency code amount based on low-frequency
subband signals of a plurality of subbands composing the
30 low-frequency component and high-frequency subband
signals of a plurality of subbands composing the high40
SP328830WO00
frequency component, and
the second high-frequency encoding unit generates
the high-frequency code string based on decoded lowfrequency
subband signals of a plurality of subbands
5 composing the decoded low-frequency component and the
high-frequency subband signals.
3. The encoding device according to claim 1, further
comprising:
10 a delay unit which delays the high-frequency code
amount, the decoded low-frequency component, and the
high-frequency component input to the second highfrequency
encoding unit.
15 4. The encoding device according to claim 1, further
comprising: a code amount adjusting unit which, when the
code amount of the high-frequency code string obtained by
the second high-frequency encoding unit is smaller than
the high-frequency code amount, makes a difference
20 between the code amount of the high-frequency code string
and the high-frequency code amount a surplus code amount
capable of being used in next and subsequent processes
and controls storage of the surplus code amount.
25 5. The encoding device according to claim 4, wherein
the surplus code amount is used for adjusting the
code amount of at least any of the high-frequency code
string and the low-frequency code string.
30 6. An encoding method of an encoding device,
comprising
41
SP328830WO00
a first high-frequency encoding unit which
calculates a high-frequency code amount being a code
amount of a high-frequency code string for obtaining a
high-frequency component based on a low-frequency
5 component and the high-frequency component of an input
signal;
a low-frequency encoding unit which encodes the
low-frequency component of the input signal to generate a
low-frequency code string;
10 a low-frequency decoding unit which decodes the
low-frequency code string;
a second high-frequency encoding unit which
generates the high-frequency code string based on a
decoded low-frequency component obtained by decoding the
15 low-frequency code string and the high-frequency
component such that the code amount of the high-frequency
code string is not larger than the high-frequency code
amount; and
a multiplexing unit which multiplexes the low-
2 0 frequency code string and the high-frequency code string
to generate an output code string,
the encoding method comprising the steps of:
calculating the high-frequency code amount by the
first high-frequency encoding unit;
25 encoding the low-frequency component by the lowfrequency
encoding unit;
decoding the low-frequency code string by the lowfrequency
decoding unit;
generating the high-frequency code string by the
30 second high-frequency encoding unit; and
generating the output code string by the
#
42
SP328830WO00
multiplexing unit.
7. A program which allows a computer to execute a
process comprising the steps of:
5 calculating a high-frequency code amount being a
code amount of a high-frequency code string for obtaining
a high-frequency component based on a low-frequency
component and the high-frequency component of an input
signal;
10 encoding the low-frequency component of the input
signal to generate a low-frequency code string;
decoding the low-frequency code string;
generating the high-frequency code string based on
a decoded low-frequency component obtained by decoding
15 the low-frequency code string and the high-frequency
component such that the code amount of the high-frequency
code string is not larger than the high-frequency code
amount; and
multiplexing the low-frequency code string and the
20 high-frequency code string to generate an output code
string.