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JP2015161839

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DESCRIPTION JP2015161839
Abstract: A signal processing apparatus capable of improving the quality of an output signal is
provided. Kind Code: A1 A pitch emphasizing gain acquiring unit for acquiring a pitch
emphasizing gain determined depending on information corresponding to a pitch period of an
input signal in a frame unit which is a predetermined time interval, a pitch of a predetermined
frequency component in the input signal And a pitch emphasis signal generation unit 12 for
generating a pitch emphasis signal which is a signal emphasized more strongly as the pitch
emphasis gain corresponding to the input signal is larger, and the pitch emphasis gain acquired
by the pitch emphasis gain acquisition unit is an input signal The shorter the pitch period, the
larger, or the higher the pitch frequency of the input signal, the larger. [Selected figure] Figure 3
Signal processing apparatus, signal processing method, program
[0001]
The present invention relates to a signal processing apparatus, a signal processing method, and a
program that perform postfiltering of digital time-series signals.
[0002]
In the encoding of speech and acoustic signals, a method of post-filtering a decoded acoustic
signal to improve the sound quality of the audibility is widely used (Non-Patent Documents 1 and
2).
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Hereinafter, the signal processing device of Non-Patent Document 1 will be described with
reference to FIG. 1 and FIG. FIG. 1 is a block diagram showing the configuration of the signal
processing device 9 of Non-Patent Document 1. As shown in FIG. FIG. 2 is a flowchart showing
the operation of the signal processing device 9 of Non-Patent Document 1. As shown in FIG. 1,
the signal processing device 9 of Non-Patent Document 1 includes a pitch improving unit 91, a
subtracting unit 92, a low pass filter unit 93, and a combining unit 94. The signal processing
device 9 performs postfiltering with these configurations. It is assumed that the input signal to
the post filter is processed for each frame of N samples, and the input signal of a certain frame is
X (n) (n = 0, 1, ..., N-1).
[0003]
The pitch improvement unit 91 obtains a pitch emphasis signal P (n) using the pitch period τ of
the input signals X (n) and X (n). Specifically, first, the pitch improvement unit 91 obtains the
emphasized intermediate signal Q (n) of the pitch according to the following equation.
[0004]
[0005]
The pitch improving unit 91 obtains a pitch emphasis signal P (n) according to the following
equation using the pitch-emphasized intermediate signal Q (n) (S91).
[0006]
[0007]
Here, a is a parameter (pitch emphasis gain) that controls attenuation of harmonics, and is a
predetermined constant.
[0008]
Here, the pitch emphasis gain a is
[0009]
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[0010]
Is calculated adaptively for each processing frame.
However, in order to prevent deterioration of the sound quality due to excessive pitch emphasis,
0 ≦ a ≦ 0.5 is set as a constraint condition.
Therefore, the pitch emphasis gain a is
[0011]
[0012]
Rounded at the upper and lower limits as.
なお、
[0013]
[0014]
Where N is the signal length used for pitch enhancement.
Cp is the inner product of X (n) and Q (n), and Ep represents the energy of Q (n).
また、
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[0015]
[0016]
である。
Here, ← indicates that the value of the parameter on the left side is updated with the value on the
right side.
Epp represents the energy of the average prediction error up to the processing frame
immediately preceding Q (n).
[0017]
In another expression, the pitch improvement unit 91 inputs the input signal X (n) in the current
time interval to the input signal x (n−τ) past the present by the pitch period τ and the future
by the pitch period τ than the present The pitch emphasis signal P (n) which is a signal which
synthesize | combined the input signal x (n + (tau)) of these is produced | generated (S91).
[0018]
Next, the subtracting unit 92 outputs a residual signal R (n) = P (n) −X (n) obtained by
subtracting the input signal X (n) of the current time interval from the pitch emphasis signal P
(n). (S92).
The low-pass filter unit 93 performs low-pass filtering with a fixed value cutoff frequency Fc =
500 Hz to extract only the frequency component of the cutoff frequency Fc = 500 Hz or less
from the residual signal R (n) n) is output (S93).
The combining unit 94 combines the input signal X (n) in the current time interval and the lowpass only residual signal r (n) output from the low-pass filter unit 93. Y (n) = X (n) ) + R (n) is
generated, and a signal Y (n) is output (S94).
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[0019]
In this manner, in the signal processing device 9 of Non-Patent Document 1, the auditory quality
is improved by emphasizing the pitch structure of the low frequency band (frequency component
of 500 Hz or less).
Further, in Non-Patent Document 2, instead of the above-described low-pass filtering, a method is
used in which pitch enhancement is performed for the entire frequency band.
[0020]
ITU-T Rec. G. 718, ITU, 2008. (7.14.1.1Section) Chen Juin-Hwey and A. Gersho, “Adaptive
postfiltering for quality enhancement of coded speech,” IEEE Transactions on Speech and Audio
Processing, Volume: 3, Issue: 1, Pages: 59-71, 1995.
[0021]
In the conventional method, the pitch emphasis signal is generated by adjusting the pitch
emphasis gain a in the range of 0 ≦ a ≦ 0.5 depending on X (n) and Q (n). Therefore, there is a
problem that the harmonic structure due to the pitch of the input signal can not be sufficiently
reproduced when the limitation is excessive, and the quality of the output signal is not
necessarily sufficiently improved. Therefore, an object of the present invention is to provide a
signal processing apparatus capable of improving the quality of an output signal.
[0022]
The signal processing apparatus of the present invention includes a pitch emphasis gain
acquisition unit and a pitch emphasis signal generation unit.
[0023]
The pitch emphasis gain acquisition unit acquires a pitch emphasis gain which is determined
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depending on information corresponding to a pitch period of an input signal in a frame unit
which is a predetermined time interval.
The pitch emphasis signal generation unit generates a pitch emphasis signal which is a signal in
which the pitch of a predetermined frequency component in the input signal is strongly
emphasized as the pitch emphasis gain corresponding to the input signal is larger.
[0024]
The pitch emphasis gain acquired by the pitch emphasis gain acquisition unit is larger as the
pitch period of the input signal is shorter or as the pitch frequency of the input signal is higher.
[0025]
According to the signal processing device of the present invention, the quality of the output
signal can be improved.
[0026]
FIG. 2 is a block diagram showing a configuration of a signal processing device of Non-Patent
Document 1.
5 is a flowchart showing the operation of the signal processing device of Non-Patent Document
1.
BRIEF DESCRIPTION OF THE DRAWINGS The block diagram which shows the structure of the
signal processing apparatus of Example 1 of this invention. The flowchart which shows operation
| movement of the signal processing apparatus of Example 1 of this invention. FIG. 8 is a block
diagram showing the configuration of a signal processing device of Modification 1 of the present
invention. 6 is a flowchart showing the operation of the signal processing device of Modification
1 of the present invention.
[0027]
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Hereinafter, embodiments of the present invention will be described in detail. Note that
components having the same function will be assigned the same reference numerals and
redundant description will be omitted.
[0028]
In the present invention, the pitch emphasis gain is changed depending on the pitch frequency
(fundamental frequency) or pitch period of the input signal in frame units which is a
predetermined time interval. Pitch emphasis emphasizes pitches in low frequency bands, but
when the pitch frequency is high (when the pitch period is short), pitch emphasis is performed
using a larger pitch emphasis gain than when the pitch frequency is low (when the pitch period is
long) I do. By adaptively changing the pitch emphasizing gain for each frame, it is possible to
properly represent the harmonic structure of the harmonic structure according to the pitch
period for the input signal of each frame, so that the sound quality can be further improved.
[0029]
<Input to Signal Processing Device> The signal processing device of the present invention
receives a time-series signal X (n) such as an audio signal or an audio signal in a frame unit
which is a predetermined time interval and pitch period information T. . An example of the sound
signal is an instrument signal of a single tone structure or the like. The time series signal X (n)
(hereinafter referred to as “input signal X (n)”) is an input signal for each frame, and an input
signal of the nth sample of a certain frame is denoted as X (n) (n = 1, 2, ..., N-1, N is the number
of samples in the frame). The input signal X (n) is a decoded acoustic signal obtained by decoding
an input code, or a signal obtained by collecting a sound from a sound source by a microphone
or the like after processing such as sound source separation or dereverberation Restored
acoustic signal. The decoded acoustic signal may be any signal as long as it is obtained by a
decoding method in a known lossy encoding / decoding method of the acoustic signal. For
example, an acoustic signal decoded by the decoder of Non-Patent Document 1, AMR, G. This is
an acoustic signal decoded based on another audio / acoustic signal compression encoding /
decoding method such as 729. That is, the input signal of the signal processing apparatus is a
signal (lossy signal) obtained by applying some signal processing to the original signal and in
which the original signal is distorted. Note that the decoder of Non-Patent Document 1, AMR, G.F.
In a decoder such as 729, acoustic signals (decoded acoustic signals) for a plurality of frames are
continuously output. Therefore, acoustic signals for a plurality of frames are continuously input
to the signal processing apparatus of the present invention.
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[0030]
The pitch period information T may be anything as long as it is information corresponding to the
pitch period of the input signal of a frame that is close to or present. The “information
corresponding to the pitch period” may be, for example, the pitch period itself, or a value
obtained by quantizing the pitch period, or an index code corresponding to the pitch period or
the quantized value thereof. May be Further, since the pitch period is the reciprocal of the pitch
frequency, the pitch frequency, a value obtained by quantizing the pitch frequency, or a pitch
frequency or an index code corresponding to the quantized value may be used as "pitch period
information T". The pitch period information T is, for example, a pitch period τ corresponding to
the input signal (decoded sound signal) X (n) obtained in the process of obtaining the decoded
sound signal from the compressed sound signal. “Pitch period τ corresponding to X (n)” may
be a pitch period of a frame X = (X (1), X (2),..., X (N−1)) including X (n), It may be a pitch period
of a frame near a frame including X (n), or an average value or a weighted average value or a
maximum value / minimum value / median value of pitch periods of a frame near a frame
including X (n) Such statistics may be used. Alternatively, the quantized value τ ′ = Round (τ)
of the pitch period τ corresponding to X (n) may be used as the pitch period τ. Here, the Round
function is a function that converts a real number value to an integer value, and may be rounded
to the nearest integer value, a floor function (truncated), or a ceiling function (rounded up).
[0031]
The signal processing apparatus according to the first embodiment will be described below with
reference to FIGS. 3 and 4. FIG. 3 is a block diagram showing the configuration of the signal
processing device 1 of this embodiment. FIG. 4 is a flowchart showing the operation of the signal
processing device 1 of the present embodiment. As shown in FIG. 3, the signal processing
apparatus 1 of the present embodiment includes a pitch emphasis gain acquisition unit 11 and a
pitch emphasis signal generation unit 12.
[0032]
[Pitch Emphasis Gain Acquisition Unit 11] The pitch emphasis gain acquisition unit 11 acquires a
pitch emphasis gain based on the input pitch period information T. In another expression, the
pitch emphasis gain acquisition unit 11 acquires a pitch emphasis gain a determined depending
on information (pitch period information T) corresponding to the pitch period of the input signal
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in a frame unit which is a predetermined time interval (S11) ). The pitch emphasis gain a is
information used to control the degree of pitch emphasis in the pitch emphasis signal generation
unit 12 described later.
[0033]
Specifically, the pitch emphasis gain acquisition unit 11 determines the pitch emphasis gain a so
that the pitch emphasis gain a becomes larger as the pitch period is shorter (pitch frequency is
higher). For example, assuming that the pitch period corresponding to the pitch period
information T is τ, and the monotonous non-increasing function for τ is g (τ), the pitch
emphasis gain acquisition unit 11 calculates a pitch emphasis gain a according to a = g (τ)
Decide. An example of the monotonous nonincreasing function g (τ) is g (τ) = 0.0036 × fs /
τ−0.1820. Here, fs is a sampling frequency.
[0034]
The value of the pitch emphasis gain a may not be a continuous monotonous nonincreasing
relationship with an increase in the value of τ, but a discrete monotonous nonincreasing
relationship. For example, with a predetermined threshold value θ, two different pitch
enhancement gains are determined as a1 and a2 (a1 <a2), and in the case of 0 <τ ≦ θ, pitch
enhancement gain a2 is determined as pitch enhancement gain a, θ < In the case of τ, the pitch
emphasis gain a1 may be determined as the pitch emphasis gain a. Alternatively, the pitch
emphasis gain a ′ of fixed value may be determined as the pitch emphasis gain a in the case of
0 <τ ≦ θ, and may be determined as the pitch emphasis gain a = g (τ) in the case of θ <τ. .
[0035]
In other words, when the information corresponding to the pitch period of the input signal is the
information corresponding to the case where the pitch period has the first value, the first pitch
emphasis gain a2 acquired by the pitch emphasis gain acquiring unit 11 is the input signal The
information corresponding to the pitch period is larger than the second pitch emphasis gain a1
acquired by the pitch emphasis gain acquisition unit 11 when the information corresponding to
the pitch period is a second value larger than the first value.
[0036]
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[Pitch Emphasizing Signal Generating Unit 12] The pitch emphasizing signal generating unit 12
receives the pitch emphasizing gain a acquired by the pitch emphasizing gain acquiring unit 11
and the input signal X (n), and inputs a predetermined signal among the input signals X (n). A
pitch emphasis signal P (n) is generated in which the pitch of frequency components below the
cutoff frequency is emphasized at a rate corresponding to the pitch emphasis gain a.
(S12)。 In another expression, the pitch emphasis signal generation unit 12 generates a
pitch emphasis signal which is a signal that emphasizes the pitch of a predetermined frequency
component in the input signal as the pitch emphasis gain corresponding to the input signal
increases.
[0037]
For example, the pitch emphasis signal generation unit 12 generates the pitch emphasis signal P
(n) by the weighted sum represented by Expression (2). As understood from the equation (2), the
pitch emphasis gain a corresponds to the degree of emphasis on the pitch below the
predetermined frequency component of the input signal. That is, the pitch emphasis signal
generation unit 12 is not limited to the weighted sum of Expression (2), and the pitch of the
frequency component of the input signal X (n) below the predetermined cutoff frequency has a
large pitch emphasis gain a. Any process may be used as long as it generates a signal that is
emphasized so strongly as the pitch emphasis signal P (n).
[0038]
<Modification 1> Hereinafter, with reference to FIG. 5, FIG. 6, the signal processing apparatus of
the modification 1 which added the modification to the pitch emphasis gain acquisition part 11
of a present Example is demonstrated. FIG. 5 is a block diagram showing the configuration of a
signal processing device 1a of this modification. FIG. 6 is a flowchart showing the operation of
the signal processing device 1a of this modification. As shown in FIG. 5, the signal processing
device 1 a of the present modified example includes a pitch emphasis gain acquisition unit 11 a
and a pitch emphasis signal generation unit 12.
[0039]
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The pitch emphasis gain acquisition unit 11a determines the pitch emphasis gain a so that the
pitch emphasis gain a is larger as the pitch frequency is higher (S11a). For example, assuming
that the pitch frequency corresponding to the pitch period information T is Fp and the
monotonous non-decreasing function for Fp is h (Fp), the pitch emphasis gain acquisition unit
11a performs a = h (Fp) according to a pitch emphasis gain a Ask for An example of the
monotonous nondecreasing function h (Fp) is h (Fp) = 0.0036 × Fp−0.1820.
[0040]
Note that the value of the pitch emphasis gain a may not be a continuous monotonous nonphenomenon relationship with an increase in the value of Fp but a discrete monotonous nonphenomenon relationship. For example, with a predetermined threshold value θ, two different
pitch enhancement gains are determined as a1 and a2 (a1 <a2), and in the case of 0 <Fp ≦ θ,
pitch enhancement gain a1 is determined as pitch enhancement gain a. In the case of Fp, the
pitch emphasis gain a2 may be determined as the pitch emphasis gain a. Alternatively, pitch
emphasis gain a = g (τ) may be determined when 0 <Fp ≦ θ, and pitch emphasis gain a ′ of a
fixed value may be determined as pitch emphasis gain a when θ <Fp. .
[0041]
In other words, when the information corresponding to the pitch period of the input signal is the
information corresponding to the case where the pitch frequency is the first value, the first pitch
emphasis gain a1 acquired by the pitch emphasis gain acquisition unit 11a is the input signal
The information corresponding to the pitch period is smaller than the second pitch emphasis
gain a2 acquired by the pitch emphasis gain acquisition unit 11a when the information
corresponding to the pitch frequency is a second value larger than the first value.
[0042]
When the above configuration is implemented by a computer, the processing content of the
function that each device should have is described by a program.
The above processing function is realized on the computer by executing this program on the
computer.
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[0043]
The program describing the processing content can be recorded in a computer readable
recording medium. As the computer readable recording medium, any medium such as a magnetic
recording device, an optical disc, a magneto-optical recording medium, a semiconductor memory,
etc. may be used.
[0044]
Further, this program is distributed, for example, by selling, transferring, lending, etc. a portable
recording medium such as a DVD, a CD-ROM or the like in which the program is recorded.
Furthermore, this program may be stored in a storage device of a server computer, and the
program may be distributed by transferring the program from the server computer to another
computer via a network.
[0045]
For example, a computer that executes such a program first temporarily stores a program
recorded on a portable recording medium or a program transferred from a server computer in its
own storage device. Then, at the time of execution of the process, the computer reads the
program stored in its own recording medium and executes the process according to the read
program. Further, as another execution form of this program, the computer may read the
program directly from the portable recording medium and execute processing according to the
program, and further, the program is transferred from the server computer to this computer
Each time, processing according to the received program may be executed sequentially. In
addition, a configuration in which the above-described processing is executed by a so-called ASP
(Application Service Provider) type service that realizes processing functions only by executing
instructions and acquiring results from the server computer without transferring the program to
the computer It may be
[0046]
Note that the program in the present embodiment includes information provided for processing
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by a computer that conforms to the program (such as data that is not a direct command to the
computer but has a property that defines the processing of the computer). Further, in this
embodiment, although the present apparatus is configured by executing a predetermined
program on a computer, at least a part of the processing contents may be realized as hardware.
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