KR101421256B1 - Apparatus and method for encoding/decoding using bandwidth extension in portable terminal - Google Patents

Abstract

The present invention relates to an apparatus and method for enhancing mutual information between a higher-band signal and a lower-band signal in order to increase a coding efficiency of a mobile terminal, and more particularly to an apparatus and a method for processing a lower-band signal of an input signal, And a filter coefficient calculation unit for calculating a filter coefficient for increasing a mutual information amount between the upper band signal of the upper band signal and the encoded lower band signal of the higher band signal, And a low-band mutual information filter for processing mutual information of the low-band signal to increase the amount of mutual information using the filter coefficient calculated by the filter coefficient calculator, Get better encoding performance than the encoding device you use .

Decoder, an encoder, a bandwidth extension method, a BWE, a high-band signal, a low-band signal

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an encoding apparatus and a method using a band extension scheme of a portable terminal,

The present invention relates to an apparatus and method for encoding and decoding a mobile terminal, and more particularly, to an apparatus and method for adjusting a correlation (mutual information amount) affecting coding efficiency in a coding apparatus of a mobile terminal using a band extension technique . In other words, the present invention relates to an apparatus and method for processing mutual information between a higher-band signal and a lower-band signal to increase the coding efficiency of the mobile terminal.

With the recent development of digital signal processing technology, audio signals are mostly stored and reproduced as digital data. The digital audio storage / playback device samples and quantizes analog audio signals, converts them into PCM (Pulse Code Modulation) audio data, which is a digital signal, and stores the data in an information storage medium such as a CD or a DVD. It is possible to hear.

When the digital system estimates and restores a lower band signal from a receiver or a feature vector extracted from the signal using an artificial bandwidth extension (BWE), only a lower band signal is reproduced The sound quality can be greatly improved.

For example, when the sampling frequency Fs of the input signal is 16 kHz, the bandwidth extension method restores the upper band signal of 4 k to 8 kHz from the lower band signal of 0 to 4 kHz to pass only signals of 4 kHz or lower, (Upper band and lower band) of a voice or audio signal in a method of finally outputting a signal of 16 kHz, which is the same as the original input signal, on the receiving side of the voice or audio signal.

 That is, when an audio signal and a voice signal of one frame are divided into a lower band and a higher band for each frequency band, since signals of both bands are generated from the same human vocal structure, there is a close correlation therebetween, Or if the mutual information is large, the high-band signal reconstructed by the bandwidth extension method will have a good sound quality close to the original sound.

However, if there is not enough mutual information between the two bands and there is no information on the upper band signal, the upper band signal can not be completely restored by the bandwidth extension method.

1 is a block diagram showing a configuration of an apparatus for performing a bandwidth extension method in a general portable terminal.

1, the portable terminal includes an encoder 100 and a decoder 110. The encoder 100 includes a lower band encoder 101, a higher band signal estimator 103, And a quantizer 105. The decoder 103 may include an inverse quantizer 112, a lower band decoder 114 and a higher band signal estimator 116 .

The encoder 100 is a BWE-based encoder that enhances coding efficiency by using a BWE system in coding an upper band signal. The lower band encoder 101 processes the lower band signal to receive and encode the lower band signal, and the upper band signal estimator 103 Estimates a higher-band signal by using the signal encoded by the lower-band encoder 101.

Accordingly, the encoder 100 subtracts the upper band signal estimated by the upper band signal estimator 103 from the input upper band signal, thereby outputting a residual upper band signal from which signals overlapping the lower band are removed do. Here, the residual upper band signal is quantized by the quantizer 105 and then transmitted through a communication channel. Here, the quantizer 105 uses a scalar or vector quantizer depending on the application purpose.

The decoder 110 processes the lower-band decoder 114 to decode the encoded lower-band signal to reproduce the lower-band signal, and the upper-band signal estimator 116 uses the decoded lower-band signal Thereby estimating the upper band signal. In addition, the dequantizer 112 dequantizes the received residual upper-band signal and outputs it as a decoded residual higher-band signal.

Accordingly, the decoder 110 processes the decoded residual high-band signal and the high-band signal estimated by the high-band signal estimator 116 so as to output a decoded high-band signal.

The above method can improve the coding efficiency of the upper band signal by removing the upper band signal overlapping with the lower band by using the upper band signal estimator on the receiving side as well as the transmitting side and then coding the remaining upper band portion, There is a problem that the performance is changed depending on the correlation or the size of the mutual information. In other words, when the correlation is large, the coding efficiency may be high, but when the correlation is small, the coding efficiency is lowered.

Accordingly, there is a need for an apparatus and a method for solving the above problems.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an apparatus and method for improving the performance of an encoding apparatus using a band extension scheme of a mobile terminal.

It is another object of the present invention to provide an apparatus and method for controlling mutual information amount between band signals in an encoding apparatus using a band extension scheme of a portable terminal.

According to an aspect of the present invention, there is provided an apparatus for encoding an input signal, the apparatus comprising: a low-band encoder for encoding a low-band signal of an input signal; A higher frequency band mutual information filter for processing the higher frequency band signal to increase the mutual information amount of the higher band signal using the filter coefficient calculated by the filter coefficient calculating unit; And a lower-band mutual information filter for processing the mutual information of the lower-band signal to increase by using the filter coefficient calculated by the filter coefficient calculator.

According to a second aspect of the present invention, there is provided a decoding apparatus using a band extension scheme, comprising: an inverse quantizer for receiving and decoding a coded residual upper band signal output in a coding process; And a high-band mutual information volume inverse filter for inversely filtering the decoded high-band signal using the calculated filter coefficient and outputting the decoded high-band signal as an original signal.

According to a third aspect of the present invention, there is provided a coding method using a band extension technique, comprising the steps of: classifying an input signal into an upper band signal and a lower band signal, Calculating a filter coefficient for increasing the amount of mutual information between the classified upper band signal and the encoded lower band signal, and outputting a signal having a higher mutual information amount between the upper band signal and the lower band signal using the calculated filter coefficient Into a second image.

According to a fourth aspect of the present invention, there is provided a decoding method using a band extension technique, comprising the steps of: receiving a coded residual high band signal output in an encoding process; Calculating a filter coefficient using the decoded signal, and filtering the decoded upper band signal using the calculated filter coefficient and outputting the inverse filtered signal as an original signal .

As described above, the present invention increases the amount of mutual information between a higher-band signal and a lower-band signal of a signal to be encoded in a mobile terminal for encoding voice and audio signals using a BWE (Artificial Bandwidth Extension) It is possible to obtain an improved coding performance over a coding apparatus using the existing bandwidth extension method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. In the following description, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

In the following description, an apparatus and method for controlling a correlation (mutual information amount) affecting coding efficiency in a coding apparatus of a mobile terminal using a band extension scheme will be described.

2 is a block diagram illustrating an encoder of a portable terminal according to an exemplary embodiment of the present invention.

2, the encoder includes an upper band inter-information amount filter 201, a quantizer 203, a filter coefficient calculation unit 205, a higher-band signal estimator 207, a lower-band mutual information filter 209, A lower-band encoder 211, a lower-band decoder 213, and a higher-band mutual information volume inverse filter 215. [

The lower-band encoder 211 of the encoder processes the lower-band signal to encode the lower-band signal and transmits the lower-band signal through a communication channel. The upper-band signal estimator 207 estimates a higher-band signal using the encoded lower- .

The lower-band mutual information filter 209 processes the encoded mutual information of the lower-band signals using the filter coefficient provided from the filter coefficient calculator 205. [

The upper band mutual information filter 201 processes the input upper band signal using the filter coefficient provided from the filter coefficient calculator 205. [ That is, the upper band mutual information filter processes the input higher band signal (higher band signal 1) to convert the input upper band signal (upper band signal 2) having mutually increased information amount.

The filter coefficient calculator 205 calculates a filter coefficient using a decoded high-band signal received from the high-band mutual information volume inverse filter and a low-band signal decoded by the low-band decoder, Band and upper-band filter coefficients, and processes the coefficients to provide each of the corresponding filters.

Here, the decoded upper band signal provided from the upper band inter-information-amount inverse filter 215 is a signal after being decoded by the upper-band encoded signal of the previous frame, and the decoded lower- The lower-band signal is a decoded signal.

The encoder receives the residual upper band signal (residual signal) obtained by subtracting the upper band signal (upper band signal 2) converted by the upper band mutual information filter 201 and the upper band signal estimated by the upper band signal estimator 207 The upper band signal 2)), and then the quantizer 203 processes the signal so as to quantize the signal.

3 is a block diagram illustrating a decoder of a portable terminal according to an exemplary embodiment of the present invention.

3, the decoder includes an inverse quantizer 301, a high-band mutual information inverse filter 303, a filter calculator 305, a high-band signal estimator 307, a low-band mutual information filter 309 And a lower-band decoder 311. The lower-

The lower-band decoder 311 of the decoder decodes the encoded lower-band signal and processes the higher-band signal estimator 307 to estimate a higher-band signal using the decoded lower-band signal.

The inverse quantizer 301 receives the encoded residual upper band signal (coded residual upper band signal 2), dequantizes it, and processes it so as to output the decoded residual upper band signal (decoded residual upper band signal 2).

The filter coefficient calculator 305 calculates a lower-band filter coefficient and a higher-band inverse filter coefficient using the decoded higher-band signal and the decoded lower-band signal, and provides the corresponding coefficients to each corresponding filter do. Here, the lower-band filter coefficient calculated by the filter calculation unit 305 is equal to the transmission-side lower-band filter coefficient for the same frame, and the upper-band inverse filter coefficient is equal to the upper-band inverse filter coefficient at the transmission side And has an inverse relationship with the upper band filter coefficient on the transmission side.

The lower-band mutual information filter 309 processes the mutual information of the decoded lower-band signal to increase by using the coefficient provided from the filter coefficient calculator 305, and then the upper-band signal estimator 307 ) So as to estimate the upper band signal.

Accordingly, the decoder decodes the decoded high-band signal (the decoded high-band signal (the decoded high-band signal) by summing the residual high-band signal decoded by the dequantizer 301 and the high-band signal estimated by the high- 2) to the upper band mutual information volume inverse filter.

The upper band mutual information amount inverse filter 303 inversely filters the decoded upper band signal (decoded upper band signal 2) using the inverse filter coefficient provided from the filter coefficient calculation unit 305, Band signal.

4 is a block diagram illustrating a configuration of a filter coefficient calculator applied to an encoder according to an embodiment of the present invention.

Referring to FIG. 4, a filter coefficient calculator 400 applied to the encoder includes a high-band inter-information-amount filter coefficient calculator 401 and a low-band inter-information-amount filter coefficient calculator 403.

Here, the upper band inter-information-amount filter coefficient calculator 401 may calculate the upper-band inter-information-amount filter coefficient calculator 401 using the upper-band signal decoded by the block for calculating the coefficient of the upper-band inter-

In addition, the lower-band mutual information filter coefficient calculator 403 may calculate the lower-band mutual information filter coefficient calculator 403 using a higher-band signal decoded by a block for calculating a coefficient of the lower-band mutual information filter and a lower-

Here, when the filter coefficient calculator 400 of the encoder calculates a filter coefficient for increasing the amount of mutual information of the upper band signal, the following condition must be satisfied.

First, the lower-band signal X, the higher-band signal Y, the higher-band filter mutual information H [], the higher-band inverse filter mutual information for the higher-band signal converted by the H ^-1 [], H [] to Y2 If so,

First, H [] must be reversible, and H = ¹ [] must exist to establish Y = H ^-1 [Y2] = H ^-1 [H [Y]]. That is, the original signal Y must be reproducible from the converted signal Y2 .

Second, the mutual information quantity I [ X; Y2 ]> I [ X; Y ] should be established.

Third, in the statistical sense, the dynamic range of Y2 should not be larger than at least the dynamic range of Y.

The condition to be satisfied in calculating the filter coefficient as described above will be described in detail in FIG.

5 is a block diagram illustrating a configuration of a filter coefficient calculator applied to a decoder according to an embodiment of the present invention.

Referring to FIG. 5, the filter coefficient calculator 500 applied to the decoder includes an upper band inter-information-amount reverse-filter-coefficient calculator 501 and a lower-band mutual information-quantity filter coefficient calculator 513. [

The upper band inter-information-amount reverse-filter coefficient calculator 501 may calculate the higher-band inter-information-amount reverse-frequency-filter coefficient calculator 501 using the upper-band signal decoded by the block for calculating the coefficients of the upper-

In addition, the lower-band mutual information filter coefficient calculator 513 may calculate the lower-band mutual information filter coefficient calculator 513 using the upper-band signal decoded by the block for calculating the coefficient of the lower-band mutual information filter and the lower-band signal decoded.

Here, the filter coefficient calculator 500 of the decoder may calculate a filter coefficient for increasing the mutual information amount of the higher-band signal in a state satisfying the condition as in the filter coefficient calculator 400 of the encoder described in FIG. 4 It must be calculated.

The above description has been made on an apparatus for adjusting a correlation (mutual information amount) that affects encoding efficiency in a coding apparatus of a mobile terminal using a band extension scheme. In the following description, the apparatus according to the preferred embodiment of the present invention A method for adjusting the correlation (mutual information amount) that affects the coding efficiency will be described.

6 is a flowchart illustrating an operation of an encoder according to an exemplary embodiment of the present invention. Here, the encoder performs a BWE (Artificial Bandwidth Extension) on the upper band of the input signal to increase mutual information between the upper band and the lower band. Accordingly, the encoder encodes the lower-band signal by performing lower-band coding and outputs the lower-band signal.

Referring to FIG. 6, the encoder first calculates a mutual information filter coefficient in step 601, and then, in step 603, transforms the input upper band signal (upper band signal 1) using the calculated filter coefficient . Here, the mutual information amount filter coefficient may be calculated by a filter coefficient unit as a coefficient of the upper band mutual information filter and a coefficient of the lower band mutual information filter, and the converted higher band signal (upper band signal 2) Output high-band signal whose mutual information amount is increased compared to the signal.

Here, the filter coefficient calculation unit should satisfy the following condition.

First, the lower-band signal X, the higher-band signal Y, the higher-band filter mutual information H [], the higher-band inverse filter mutual information for the higher-band signal converted by the H ^-1 [], H [] to Y2 If so,

First, H [] must be reversible, and H = ¹ [] must exist to establish Y = H ^-1 [Y2] = H ^-1 [H [Y]]. That is, the original signal Y must be reproducible from the converted signal Y2 .

Second, the mutual information quantity I [ X; Y2 ]> I [ X; Y ] should be established.

Third, in the statistical sense, the dynamic range of Y2 should not be larger than at least the dynamic range of Y.

The first condition means that the signal converted by the transmitting side upper band mutual information filter should be recoverable by the receiving upper band mutual information quantity inverse filter and the second and third condition means that the result of conversion by filter H [ It should contribute to the improvement of efficiency.

In order for the first condition, H ^-1 [], to exist, the filter H [] basically represents a monotonic & differentiable function, but the mutual information amount does not change with respect to this conversion function. That is, I [ X; Y2 ] = I [ X; Y ]. Therefore, it does not satisfy the second condition.

In consideration of this problem, the present invention uses a meaning ("reversible") collectively referred to as a function enabling reproduction of the originally transmitted information Y finally using other information transmitted, for example, .

For example, Y2 = H [ X, Y ] = X * Y = {x1y1, ..., xNyN} '. Here, "· *" means multiplication between components, and x1, y1, etc. denote components of X and Y, respectively. The inverse function H ^-1 [], that is, the function of regenerating Y from Y2 again under the condition that X is given can be defined as follows. That is, Y = H ^-1 [ X, Y2 ] = X / Y2 = {x1 / y21, ..., xN / y2N} '. Here, "· /" means a division operation between components, and x1, y21, etc. denote components of X and Y2, respectively.

Thus, Y2 sent from the sender using the function "· *" can be restored to Y again using the function "· /" on the receiver side. In relation to the second condition, mutual information increases in general when two random variables (or vectors) have mutual dependency, that is, a mutual function relationship. That is, if the Y2 transformed by the filter H [] has a functional relationship of X and some function relation, for example, Y2 = f [ X ], the mutual information amount of the two random vectors Y2 and X increases.

In step 605, the encoder processes the lower-band mutual information filter to estimate a higher-band signal, and then proceeds to step 607 so as to output a residual higher-band signal (residual upper-band signal 2)).

Here, the residual upper band output signal is a signal obtained by subtracting the upper band signal (upper band signal 2) converted in step 603 and the upper band signal estimated in step 605. [

In step 609, the encoder processes the residual signal so as to be quantized, and processes it so as to transmit the encoded residual high-band signal 2 through a communication channel. Here, the quantizer for quantizing the residual signal may use a scalar or a vector quantizer depending on the application purpose.

Thereafter, the encoder ends the present algorithm.

7 is a flowchart illustrating an operation of a decoder according to an exemplary embodiment of the present invention. Here, the decoder processes the input signal in which the amount of mutual information between the upper band and the lower band is increased. Accordingly, the decoder decodes the encoded lower-band signal received through the communication channel into a lower-band decoder to reproduce the lower-band signal.

Referring to FIG. 7, in step 701, the decoder receives a residual signal of the upper band transformed by the encoder (the encoded residual upper band signal 2).

Thereafter, the decoder proceeds to step 703 to process the received residual signal to be quantized, and then proceeds to step 705 so as to decode it into a higher-band signal. That is, the decoder processes the received encoded residual higher band signal 2 into a decoded residual higher band signal 2.

Then, the decoder proceeds to step 707 and calculates a filter coefficient using the decoded signal. Here, the filter coefficient refers to a lower band filter coefficient and a higher band inverse filter coefficient, and the decoder can calculate the filter coefficient using the decoded upper band signal and the decoded lower band signal. In addition, the lower-band filter coefficient is the same as the transmission-side lower-band filter coefficient for the same frame, and the upper-band inverse filter coefficient is the same as the upper-band inverse filter coefficient at the transmitting side and is inversely related to the upper- .

Then, the decoder proceeds to step 709 to decode the original high-band signal.

The decoding of the original higher-band signal is performed by summing the residual upper-band signal 2, which has been decoded in step 705, and the upper-band signal estimated by the higher-band signal estimator, And then decodes the decoded upper band signal into an original upper band signal.

Thereafter, the decoder ends the algorithm.

FIG. 8 is a flowchart illustrating a process of calculating a filter coefficient of a filter calculation unit according to an embodiment of the present invention.

Referring to FIG. 8, in step 801, the filter calculator determines a decoded upper band signal of a previous frame, and then proceeds to step 803 to calculate a higher band filter coefficient. That is, the filter calculator calculates a filter for increasing the mutual information amount of the input upper band signal using the decoded signal higher band signal of the previous frame.

In step 805, the filter calculator determines a decoded lower-band signal, and then proceeds to step 807 to calculate a lower-band filter coefficient. Here, the filter calculator calculates a filter for increasing the mutual information amount of the input signal using the decoded lower-band signal, which is the decoded signal of the encoded lower-band signal of the current frame.

Thereafter, the filter calculation unit ends the algorithm.

Although the present invention has been described with respect to an apparatus and method for increasing the amount of mutual information between a higher band signal and a lower band signal according to the present invention, a method of using a filter coefficient of a higher band signal and a filter coefficient of a higher band signal has been proposed. It is possible to increase the mutual information amount of the upper band signal and the lower band signal by applying only the mutual information quantity filter or applying only the lower band mutual information quantity filter.

The method of applying only the higher-band mutual information filter or applying the lower-band mutual information filter alone is the same as the method of using the higher-band mutual information filter and the lower-band mutual information filter described in FIGS. 2 to 8, The amount of mutual information between the upper band signal and the lower band signal can be increased.

9 is a graph illustrating performance of a decoder according to an embodiment of the present invention.

The present invention is a method for increasing the amount of mutual information between a higher band vector and a lower band vector, as described above, a method of applying a higher band mutual information filter and a lower band mutual information filter, Can be applied.

9 illustrates a method of applying only the upper band mutual information filter and a case of applying only the lower band mutual information filter according to an embodiment of the present invention.

First, in order to compare the performance of a general portable terminal encoding apparatus and a portable terminal encoding apparatus according to the present invention, a lower frequency band of a PCM voice signal sampled at 16 kHz is divided into a total of 14 differential MFCC (Mel Frequency Cepstral Coefficient) (N) = {x1 (n), ..., x14 (n), lnELB (n)} ', and the corresponding upper band signal is transformed into the fourth order MFCC coefficient and log (N) = {y1 (n), ..., y4 (n), lnEHB (n)} '. Here, n indicates the frame number and the frame size is 20 ms. In this case, the encoding problem is to effectively encode the fourth-order upper band MFCC coefficient and energy information Y (n).

First, when it is assumed that only the upper band signal E _HB of the Y (n) information is coded prior to the description of the operation procedure of the encoder by applying only the upper band mutual information filter, the upper band signal is Y ) = {lnE _HB (n)}. Here, an example of the upper band mutual information filter for converting the original upper band signal Y (n) into Y2 (n) can be expressed as Equation (1) below.

Y2 (n) = H [X (n), Y (n-1)] = lnE HB (n) -lnE LB (n) = ln (E HB (n) / E LB (n))

Here, X denotes a lower band signal, Y denotes a higher band signal, H [] denotes a higher band mutual information quantity filter, Y2 denotes a higher band signal converted by H [], E _HB Is the energy of the upper band signal, and E _LB is the energy of the lower band signal. Also, Y (n-1) indicates the coded upper band vector of the n-1th frame fed back.

Referring to Equation (1), the upper band mutual information filter corresponds to a difference operation on a log scale and the division operation on a linear scale.

In the above-described upper band mutual information filter, the first condition (H [] of the three conditions presented in the present invention must be reversible and H ^-1 [] exists so that Y = H ^-1 [Y 2] = H ^-1 [H [Y]] must be established, that is, the original signal Y must be reproducible from the converted signal Y2 ). That is, the original higher-band signal can be recovered from lnELB (n), which is one component of the upper-band signal Y2 and the lower-band signal X (n), which are transformed by the upper-band inter- This can be expressed as Equation (2).

lnE _HB (n) = Y2 (n) + lnE _LB (n)

Here, E _HB E _LB represents the energy of the lower band signal, and Y 2 represents the upper band signal converted by the higher band mutual information filter.

The above-mentioned Equation (1) can be expressed as Equation (3), and the second condition among the three conditions (mutual information quantity I [ X; Y2 ]> I [ X; Y ] Should be satisfied.

I [X (n); Y2 (n)] = 0.71

Here, X represents a lower band signal, Y represents a higher band signal, and Y2 represents a higher band signal converted by the higher band mutual information filter.

Referring to Equation (3), the mutual information amount of Y2 is increased by about 0.56 bits compared with the mutual information amount of Y. [ This shows a coding efficiency improvement of 0.56 bits per frame and 28 bits per second in the coding problem of the upper band energy Y (n) = {lnE _HB (n)}. Finally, the dispersion of Y was about 74.44 and the dispersion of Y2 was about 35.06. Therefore, like the <Equation 1> it is (and should be no greater than the dynamic range of the dynamic range (dynamic range) of Y2 in the statistical mean at least Y.) The third condition presented in the present invention satisfies.

The mutual information amount between the two vectors shown in Equation (3) can be defined as Equation (4) below.

Here, X represents the feature vector of the lower-band signal, and Y represents the feature vector of the higher-band signal. F _X (x) is the probability density function of X, f _Y (y) is the probability density function of Y, and f _XY (x, y) is the combined probability density function of X and Y.

As described above, the filter defined in Equation (1) satisfies all three conditions provided by the present invention as the upper band mutual information filter, and the coding efficiency of the higher band energy Y (n) = {lnE _HB (n) .

Table 1 below shows the results of a comparison between the performance of a general encoder (BWE) and the performance of an encoder (eBWE) according to the present invention. FIG. 9 (a) A comparison between the performance of a coding apparatus using only a filter and the performance of a coding apparatus of a general portable terminal is shown.

Number of quantization bits BWE eBWE 0 74.44139682 35.04823669 One 29.9638428 14.41622256 2 10.48636178 4.902777868 3 3.237544251 1.483840889 4 0.879504628 0.412519595 5 0.228972655 0.108508489 6 0.058430905 0.028144785 7 0.014838623 0.007102297 8 0.003612276 0.001717147

The values in Table 1 indicate coding error energy, which indicates that the coding apparatus according to the present invention has improved coding performance compared to the coding apparatus of the conventional coding apparatus.

In another embodiment of the apparatus, an operation process of the encoder by applying only the lower-band mutual information filter is described as follows.

If it is assumed that the coding apparatus encodes only the MFCC coefficients of the fourth-order higher-order band among the Y (n) information prior to the description of the method of enhancing the coding efficiency by applying only the lower-band mutual information filter as described above, n) = {y1 (n), ..., y4 (n)}. Here, an example of the lower-band mutual information filter for converting the original lower-band signal X (n) into X2 (n) can be expressed as Equation (5).

X2 (n) = G [X (n), Y (n-1)] = {X (n): Y (n-1)} '

x1 (n), ..., x14 (n): y1 (n-1), ..., y4 (n-

Here, X denotes a lower-band signal, Y denotes a higher-band signal, G [] denotes a lower-band mutual information quantity filter, X2 denotes a lower-band signal converted by G [ (n-1) indicates the coded upper band vector of the (n-1) th feedback frame.

As shown in Equation (5), the lower-band mutual information filter represents an augmentation operator for outputting an augmented vector.

The lower-band mutual information filter satisfies the second condition among the three requirements of the mutual information filter of the present invention, and the mutual information amount is increased by the extension vector X2 as shown in Equation (6) below.

I [ X ; Y ] = 2.369886 & gt ; I [ X; Y ] = 1.439137 (unit bit)

According to the mutual information amount calculation result as shown in Equation (6), the mutual information amount increases by about 1 bit by changing from the lower band signal X to X2 . This makes it possible to predict a coding efficiency improvement of 1 bit per frame and 50 bits per second in the problem of encoding the fourth-order higher-order MFCC coefficient Y. [ In addition, the first and third conditions of the mutual information filter requirement of the present invention are related to the higher-band mutual information filter and are not applicable when only the lower-band mutual information filter is used.

Table 2 below shows a result of comparing the performance of a general encoder BWE with the performance of an encoder eBWE according to the present invention. FIG. 9 (b) A comparison between the performance of a coding apparatus using only a filter and the performance of a coding apparatus of a general portable terminal is shown.

Number of quantization bits BWE (CD) eBWE (CD) 2 0.410244 0.3954 3 0.293181 0.260144 4 0.21433 0.176756 5 0.155101 0.122713 6 0.112254 0.0866 7 0.081301 0.061116 8 0.058495 0.043185

The values in Table 2 indicate Cepstral Distance values, and it can be seen that the coding apparatus according to the present invention has improved coding performance of a general coding apparatus.

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but is capable of various modifications within the scope of the invention. Therefore, the scope of the present invention should not be limited by the illustrated embodiments, but should be determined by the scope of the appended claims and equivalents thereof.

1 is a block diagram showing a configuration of an apparatus for performing a bandwidth extension method in a general portable terminal,

2 is a block diagram illustrating an encoder of a portable terminal according to an exemplary embodiment of the present invention.

3 is a block diagram illustrating a decoder of a portable terminal according to an exemplary embodiment of the present invention.

4 is a block diagram illustrating a configuration of a filter coefficient calculation unit applied to an encoder according to an embodiment of the present invention.

5 is a block diagram illustrating a configuration of a filter coefficient calculator applied to a decoder according to an embodiment of the present invention.

FIG. 6 is a flowchart illustrating an operation of an encoder according to an exemplary embodiment of the present invention. FIG.

FIG. 7 is a flowchart illustrating an operation of a decoder according to an exemplary embodiment of the present invention,

FIG. 8 is a flowchart illustrating a process of calculating a filter coefficient of a filter calculation unit according to a preferred embodiment of the present invention. FIG.

9A is a graph comparing performance of an encoding apparatus using only a high-band inter-information-amount filter and an encoding apparatus in a general portable terminal according to a preferred embodiment of the present invention,

FIG. 9 (b) is a graph comparing the performance of a coding apparatus using only a lower-band mutual information filter and a coding apparatus in a general mobile terminal according to a preferred embodiment of the present invention.

Claims (22)

In an encoding apparatus using a band extension scheme, A lower-band encoder for encoding a lower-band signal of an input signal; A filter coefficient calculator for calculating a filter coefficient for increasing a mutual information amount between the upper band signal of the input signal and the encoded lower band signal; An upper band mutual information quantity filter for processing mutual information quantity of the higher band signal to be higher by using the filter coefficient calculated by the filter coefficient calculation unit, And a lower-band mutual information filter for processing the mutual information of the lower-band signal so as to increase the mutual information using the filter coefficient calculated by the filter coefficient calculator. The method according to claim 1, The encoding apparatus using the band extension scheme comprises: An upper band estimator for estimating a higher band signal using the lower band signal having the higher mutual information amount and processing to output a residual higher band signal obtained by subtracting the estimated upper band signal and the higher band signal having an increased mutual information amount, And a quantizer for quantizing and outputting the residual upper band signal. 3. The method of claim 2, Wherein the quantizer comprises: And quantizes the residual upper band signal using at least one of a scalar quantizer and a vector quantizer. The method according to claim 1, Wherein the filter coefficient calculator comprises: Must be the original signal Y are reproduced from the converted signals Y2, and mutual information I [X; Y2] is I [X; Y] be greater than, and the dynamic range of Y2 in the statistical significance (dynamic range) is of at least Y And calculates a filter coefficient satisfying a condition that should not be larger than the dynamic range. Here, X is a lower band signal, Y is The upper band signal, H [] is a higher band mutual information quantity filter, H ^{- 1} [] is a higher band mutual information quantity inverse filter, and Y2 is a higher band signal converted by H []. 5. The method of claim 4, Wherein the filter coefficient calculator comprises: And calculates the filter coefficient using the decoded upper band signal and the decoded lower band signal. The method according to claim 1, The encoding apparatus using the band extension scheme comprises: Wherein the control unit increases the mutual information amount using only one of the higher-band mutual information filter and the lower-band mutual information filter. In a decoding apparatus using a band extension scheme, An inverse quantizer for receiving and decoding the coded residual high band signal outputted in the coding process, A filter coefficient calculation unit for calculating a filter coefficient using a decoded signal, And a high-order band-inter-information-quantity inverse filter for inversely filtering the decoded high-band signal using the calculated filter coefficients and outputting the resultant signal as an original signal. 8. The method of claim 7, Wherein the upper band inter- And decodes the higher-band signal obtained by summing the signal obtained by decoding the encoded residual higher-band signal and the higher-band signal estimated using the lower-band signal having the higher mutual information amount. 8. The method of claim 7, Wherein the inverse quantizer comprises: A scalar inverse quantizer, a vector inverse quantizer, a scalar inverse quantizer, and a vector inverse quantizer. 8. The method of claim 7, Wherein the filter coefficient calculator comprises: Must be the original signal Y are reproduced from the converted signals Y2, and mutual information I [X; Y2] is I [X; Y] be greater than, and the dynamic range of Y2 in the statistical significance (dynamic range) is of at least Y And calculates a filter coefficient satisfying a condition that should not be larger than a dynamic range. Here, X is a lower band signal, Y is The upper band signal, H [] is a higher band mutual information quantity filter, H ^{- 1} [] is a higher band mutual information quantity inverse filter, and Y2 is a higher band signal converted by H []. 11. The method of claim 10, Wherein the filter coefficient calculator comprises: And calculates the filter coefficient using the decoded higher-band signal and the decoded lower-band signal. In a coding method using a band extension technique, Classifying an input signal into an upper band signal and a lower band signal, and encoding the lower band signal; Calculating a filter coefficient for increasing a mutual information amount between the classified upper band signal and the encoded lower band signal; And converting the higher-band signal and the lower-band signal into a signal having a higher mutual information amount by using the calculated filter coefficient. 13. The method of claim 12, In the encoding method using the band extension technique, Estimating a higher-band signal using the lower-band signal having the higher mutual information amount; Outputting a residual upper-band signal obtained by subtracting the estimated upper-band signal and a higher-band signal having an increased mutual information amount; And outputting the residual higher band signal. 13. The method of claim 12, The residual higher band signal, A scalar quantizer, and a vector quantizer. 13. The method of claim 12, Wherein the filter coefficients for increasing the mutual information amount include: Must be the original signal Y are reproduced from the converted signals Y2, and mutual information I [X; Y2] is I [X; Y] be greater than, and the dynamic range of Y2 in the statistical significance (dynamic range) is of at least Y Is not greater than the dynamic range. Here, X is a lower band signal, Y is The upper band signal, H [] is a higher band mutual information quantity filter, H ^{- 1} [] is a higher band mutual information quantity inverse filter, and Y2 is a higher band signal converted by H []. 16. The method of claim 15, Wherein the filter coefficients for increasing the mutual information amount include: Wherein the decoding is performed using the decoded upper band signal and the decoded lower band signal. 13. The method of claim 12, In the encoding method using the band extension technique, Wherein the mutual information amount of at least one of the upper band signal and the lower band signal is increased. In a decoding method using a band extension technique, Receiving a coded residual high-band signal output in a coding process; Decoding the received residual residual high-band signal; Calculating a filter coefficient using a decoded signal, Filtering the decoded upper band signal using the calculated filter coefficients, and outputting the decoded upper band signal as an original signal. 19. The method of claim 18, Wherein the inverse filtering of the decoded higher-band signal comprises: And decoding the higher-band signal obtained by summing the signal obtained by decoding the encoded residual higher-band signal and the higher-band signal estimated using the lower-band signal having a higher mutual information amount. 19. The method of claim 18, The coded residual upper band signal may include: Scalar inverse quantizer, vector inverse quantizer, and scalar inverse quantizer. 19. The method of claim 18, The calculated filter coefficient may be expressed as: Must be the original signal Y are reproduced from the converted signals Y2, and mutual information I [X; Y2] is I [X; Y] be greater than, and the dynamic range of Y2 in the statistical significance (dynamic range) is of at least Y The dynamic range is not larger than the dynamic range. Here, X is a lower band signal, Y is The upper band signal, H [] is a higher band mutual information quantity filter, H ^{- 1} [] is a higher band mutual information quantity inverse filter, and Y2 is a higher band signal converted by H []. 22. The method of claim 21, The calculated filter coefficient may be expressed as: And decodes the decoded higher-band signal and the decoded lower-band signal.

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