Patent ID: 12223971

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention are described hereinafter with reference to the attached drawings. Note that, where possible, the same elements are denoted by the same reference numerals and redundant description thereof is omitted.

First Embodiment

FIG.1is a view showing the configuration of an audio decoding device10according to a first embodiment. A communication device of the audio decoding device10receives an encoded sequence of an audio signal and outputs a decoded audio signal to the outside. As shown inFIG.1, the audio decoding device10functionally includes a decoding unit10aand a selective temporal envelope shaping unit10b.

FIG.2is a flowchart showing the operation of the audio decoding device10according to the first embodiment.

The decoding unit10adecodes an encoded sequence and generates a decoded signal (Step S10-1).

The selective temporal envelope shaping unit10breceives decoding related information, which is information obtained when decoding the encoded sequence, and the decoded signal from the decoding unit, and selectively shapes the temporal envelope of the decoded signal component into a desired temporal envelope (Step S10-2). Note that, in the following description, the temporal envelope of a signal indicates the variation of the energy or power (and a parameter equivalent to those) of the signal in the time direction.

FIG.3is a view showing the configuration of a first example of the decoding unit10ain the audio decoding device10according to the first embodiment. As shown inFIG.3, the decoding unit10afunctionally includes a decoding/inverse quantization unit10aA, a decoding related information output unit10aB, and a time-frequency inverse transform unit10aC.

FIG.4is a flowchart showing the operation of the first example of the decoding unit10ain the audio decoding device10according to the first embodiment. The decoding/inverse quantization unit10aA performs at least one of decoding and inverse quantization of an encoded sequence in accordance with the encoding scheme of the encoded sequence and thereby generates a decoded signal in the frequency domain (Step S10-1-1).

The decoding related information output unit10aB receives decoding related information, which is information obtained when generating the decoded signal in the decoding/inverse quantization unit10aA, and outputs the decoding related information (Step S10-1-2). The decoding related information output unit10aB may receive an encoded sequence, analyze it to obtain decoding related information, and output the decoding related information. For example, the decoding related information may be the number of encoded bits in each frequency band or equivalent information (for example, the average number of encoded bits per one frequency component in each frequency band). The decoding related information may be the number of encoded bits in each frequency component. The decoding related information may be the quantization step size in each frequency band. The decoding related information may be the quantization value of a frequency component. The frequency component is a transform coefficient of specified time-frequency transform, for example. The decoding related information may be the energy or power in each frequency band. The decoding related information may be information that presents a specified frequency band(s) (or frequency component). Further, when another processing related to temporal envelope shaping is included in the generation of a decoded signal, for example, the decoding related information may be information concerning the temporal envelope shaping processing, such as at least one of information as to whether or not to perform the temporal envelope shaping processing, information concerning a temporal envelope shaped by the temporal envelope shaping processing, and information about the strength of temporal envelope shaping of the temporal envelope shaping processing, for example. At least one of the above examples is output as the decoding related information.

The time-frequency inverse transform unit10aC transforms the decoded signal in the frequency domain into the decoded signal in the time domain by specified time-frequency inverse transform and outputs it (Step S10-1-3). Note that however, the time-frequency inverse transform unit10aC may output the decoded signal in the frequency domain without performing the time-frequency inverse transform. This corresponds to the case where the selective temporal envelope shaping unit10brequests a signal in the frequency domain as an input signal, for example.

FIG.5is a view showing the configuration of a second example of the decoding unit10ain the audio decoding device10according to the first embodiment. As shown inFIG.5, the decoding unit10afunctionally includes an encoded sequence analysis unit10aD, a first decoding unit10aE, and a second decoding unit10aF.

FIG.6is a flowchart showing the operation of the second example of the decoding unit10ain the audio decoding device10according to the first embodiment.

The encoded sequence analysis unit10aD analyzes an encoded sequence and divides it into a first encoded sequence and a second encoded sequence (Step S10-1-4).

The first decoding unit10aE decodes the first encoded sequence by a first decoding scheme and generates a first decoded signal, and outputs first decoding related information, which is information concerning this decoding (Step S10-1-5).

The second decoding unit10aF decodes, using the first decoded signal, the second encoded sequence by a second decoding scheme and generates a decoded signal, and outputs second decoding related information, which is information concerning this decoding (Step S10-1-6). In this example, the first decoding related information and the second decoding related information in combination are decoding related information.

FIG.7is a view showing the configuration of the first decoding unit of the second example of the decoding unit10ain the audio decoding device10according to the first embodiment. As shown inFIG.7, the first decoding unit10aE functionally includes a first decoding/inverse quantization unit10aE-a and a first decoding related information output unit10aE-b.

FIG.8is a flowchart showing the operation of the first decoding unit of the second example of the decoding unit10ain the audio decoding device10according to the first embodiment.

The first decoding/inverse quantization unit10aE-a performs at least one of decoding and inverse quantization of a first encoded sequence in accordance with the encoding scheme of the first encoded sequence and thereby generates and outputs the first decoded signal (Step S10-1-5-1).

The first decoding related information output unit10aE-b receives first decoding related information, which is information obtained when generating the first decoded signal in the first decoding/inverse quantization unit10aE-a, and outputs the first decoding related information (Step S10-5-2). The first decoding related information output unit10aE-b may receive the first encoded sequence, analyze it to obtain the first decoding related information, and output the first decoding related information. Examples of the first decoding related information may be the same as the examples of the decoding related information that is output from the decoding related information output unit10aB. Further, the first decoding related information may be information indicating that the decoding scheme of the first decoding unit is a first decoding scheme. Further, the first decoding related information may be information indicating the frequency band(s) (or frequency component(s)) contained in the first decoded signal (the frequency band(s) (or frequency component(s)) of the audio signal encoded into the first encoded sequence).

FIG.9is a view showing the configuration of the second decoding unit of the second example of the decoding unit10ain the audio decoding device10according to the first embodiment. As shown inFIG.9, the second decoding unit10aF functionally includes a second decoding/inverse quantization unit10aF-a, a second decoding related information output unit10aF-b, and a decoded signal synthesis unit10aF-c.

FIG.10is a flowchart showing the operation of the second decoding unit of the second example of the decoding unit10ain the audio decoding device10according to the first embodiment.

The second decoding/inverse quantization unit10aF-1performs at least one of decoding and inverse quantization of a second encoded sequence in accordance with the encoding scheme of the second encoded sequence and thereby generates and outputs the second decoded signal (Step S10-1-6-1). The first decoded signal may be used in the generation of the second decoded signal. The decoding scheme (second decoding scheme) of the second decoding unit may be bandwidth extension, and it may be bandwidth extension using the first decoded signal. Further, as described in Patent Literature 1 (Japanese Unexamined Patent Publication No. H9-153811), the second decoding scheme may be a decoding scheme which corresponds to the encoding scheme that makes approximation of a transform coefficient(s) in a frequency band(s) where the number of bits allocated by the first encoding scheme is smaller than a specified threshold to a transform coefficient(s) in another frequency band(s) as the second encoding scheme. Alternatively, as described in Patent Literature 2 (U.S. Pat. No. 7,447,631), the second decoding scheme may be a decoding scheme which corresponds to the encoding scheme that generates a pseudo-noise signal or reproduces a signal with another frequency component by the second encoding scheme for a frequency component that is quantized to zero by the first encoding scheme. The second decoding scheme may be a decoding scheme which corresponds to the encoding scheme that makes approximation of a certain frequency component by using a signal with another frequency component by the second encoding scheme. A frequency component that is quantized to zero by the first encoding scheme can be regarded as a frequency component that is not encoded by the first encoding scheme. In those cases, a decoding scheme corresponding to the first encoding scheme may be a first decoding scheme, which is the decoding scheme of the first decoding unit, and a decoding scheme corresponding to the second encoding scheme may be a second decoding scheme, which is the decoding scheme of the second decoding unit.

The second decoding related information output unit10aF-b receives second decoding related information that is obtained when generating the second decoded signal in the second decoding/inverse quantization unit10aF-a and outputs the second decoding related information (Step S10-1-6-2). Further, the second decoding related information output unit10aF-b may receive the second encoded sequence, analyze it to obtain the second decoding related information, and output the second decoding related information. Examples of the second decoding related information may be the same as the examples of the decoding related information that is output from the decoding related information output unit10aB.

Further, the second decoding related information may be information indicating that the decoding scheme of the second decoding unit is the second decoding scheme. For example, the second decoding related information may be information indicating that the second decoding scheme is bandwidth extension. Further, for example, information indicating a bandwidth extension scheme for each frequency band of the second decoded signal that is generated by bandwidth extension may be used as the second decoding information. The information indicating a bandwidth extension scheme for each frequency band may be information indicating reproduction of a signal using another frequency band(s), approximation of a signal in a certain frequency to a signal in another frequency, generation of a pseudo-noise signal, addition of a sinusoidal signal and the like, for example. Further, in the case of making approximation of a signal in a certain frequency to a signal in another frequency, it may be information indicating an approximation method. Furthermore, in the case of using whitening when approximating a signal in a certain frequency to a signal in another frequency, information concerning the strength of the whitening may be used as the second decoding information. Further, for example, in the case of adding a pseudo-noise signal when approximating a signal in a certain frequency to a signal in another frequency, information concerning the level of the pseudo-noise signal may be used as the second decoding information. Furthermore, for example, in the case of generating a pseudo-noise signal, information concerning the level of the pseudo-noise signal may be used as the second decoding information.

Further, for example, the second decoding related information may be information indicating that the second decoding scheme is a decoding scheme which corresponds to the encoding scheme that performs one or both of approximation of a transform coefficient(s) in a frequency band(s) where the number of bits allocated by the first encoding scheme is smaller than a specified threshold to a transform coefficient(s) in another frequency band(s) and addition (or substitution) of a transform coefficient(s) of a pseudo-noise signal. For example, the second decoding related information may be information concerning the approximation method of a transform coefficient(s) in a certain frequency band(s). For example, in the case of using a method of whitening a transform coefficient(s) in another frequency band(s) as the approximation method, information concerning the strength of the whitening may be used as the second decoding information. Further, information concerning the level of the pseudo-noise signal may be used as the second decoding information.

Further, for example, the second decoding related information may be information indicating that the second encoding scheme is an encoding scheme that generates a pseudo-noise signal or reproduces a signal with another frequency component for a frequency component that is quantized to zero by the first encoding scheme (that is, not encoded by the first encoding scheme). For example, the second decoding related information may be information indicating whether each frequency component is a frequency component that is quantized to zero by the first encoding scheme (that is, not encoded by the first encoding scheme). For example, the second decoding related information may be information indicating whether to generate a pseudo-noise signal or reproduce a signal with another frequency component for a certain frequency component. Further, for example, in the case of reproducing a signal with another frequency component for a certain frequency component, the second decoding related information may be information concerning a reproduction method. The information concerning a reproduction method may be the frequency of a source component of the reproduction, for example. Further, it may be information as to whether or not to perform processing on a source frequency component of the reproduction and information concerning processing to be performed during the reproduction, for example. Further, in the case where the processing to be performed on a source frequency component of the reproduction is whitening, for example, it may be information concerning the strength of the whitening. Furthermore, in the case where the processing to be performed on a source frequency component of the reproduction is addition of a pseudo-noise signal, it may be information concerning the level of the pseudo-noise signal.

The decoded signal synthesis unit10aF-c synthesizes a decoded signal from the first decoded signal and the second decoded signal and outputs it (Step S10-1-6-3). In the case where the second encoding scheme is bandwidth extension, the first decoded signal is a signal in a low frequency band(s) and the second decoded signal is a signal in a high frequency band(s) in general, and the decoded signal has the both frequency bands.

FIG.11is a view showing the configuration of a first example of the selective temporal envelope shaping unit10bin the audio decoding device10according to the first embodiment. As shown inFIG.11, the selective temporal envelope shaping unit10bfunctionally includes a time-frequency transform unit10bA, a frequency selection unit10bB, a frequency selective temporal envelope shaping unit10bC, and a time-frequency inverse transform unit10bD.

FIG.12is a flowchart showing the operation of the first example of the selective temporal envelope shaping unit10bin the audio decoding device10according to the first embodiment.

The time-frequency transform unit10bA transforms a decoded signal in the time domain into a decoded signal in the frequency domain by specified time-frequency transform (Step S10-2-1). Note that however, when the decoded signal is a signal in the frequency domain, the time-frequency transform unit10bA and Step S10-2-1can be omitted.

The frequency selection unit10bB selects a frequency band(s) of the frequency-domain decoded signal where temporal envelope shaping is to be performed by using at least one of the frequency-domain decoded signal and the decoding related information (Step S10-2-2). In this frequency selection step, a frequency component where temporal envelope shaping is to be performed may be selected. The frequency band(s) (or frequency component(s)) to be selected may be a part of or the whole of the frequency band(s) (or frequency component(s)) of the decoded signal.

For example, in the case where the decoding related information is the number of encoded bits in each frequency band, a frequency band(s) where the number of encoded bits is smaller than a specified threshold may be selected as the frequency band(s) where temporal envelope shaping is to be performed. Likewise, in the case where the decoding related information is equivalent information to the number of encoded bits in each frequency band, the frequency band(s) where temporal envelope shaping is to be performed can be selected by comparison with a specified threshold as a matter of course. Further, in the case where the decoding related information is the number of encoded bits in each frequency component, for example, a frequency component where the number of encoded bits is smaller than a specified threshold may be selected as the frequency component where temporal envelope shaping is to be performed. For example, a frequency component where a transform coefficient(s) is not encoded may be selected as the frequency component where temporal envelope shaping is to be performed. Further, for example, in the case where the decoding related information is the quantization step size in each frequency band, a frequency band(s) where the quantization step size is larger than a specified threshold may be selected as the frequency band(s) where temporal envelope shaping is to be performed. Further, in the case where the decoding related information is the quantization value of a frequency component, for example, the frequency band(s) where temporal envelope shaping is to be performed may be selected by comparing the quantization value with a specified threshold. For example, a component where a quantization transform coefficient(s) is smaller than a specified threshold may be selected as the frequency component where temporal envelope shaping is to be performed. Further, in the case where the decoding related information is the energy or power in each frequency band, for example, the frequency band(s) where temporal envelope shaping is to be performed may be selected by comparing the energy or power with a specified threshold. For example, when the energy or power in a frequency band(s) where selective temporal envelope shaping is to be performed is smaller than a specified threshold, it can be determined that temporal envelope shaping is not performed in this frequency band(s).

Further, in the case where the decoding related information is information concerning another temporal envelope shaping processing, a frequency band(s) where this temporal envelope shaping processing is not to be performed may be selected as the frequency band(s) where temporal envelope shaping according to the present invention is to be performed.

Further, in the case where the decoding unit10ahas the configuration described as the second example of the decoding unit10aand the decoding related information is the encoding scheme of the second decoding unit, a frequency band(s) to be decoded by the second decoding unit by a scheme corresponding to the encoding scheme of the second decoding unit may be selected as the frequency band(s) where temporal envelope shaping is to be performed. For example, when the encoding scheme of the second decoding unit is bandwidth extension, a frequency band(s) to be decoded by the second decoding unit may be selected as the frequency band(s) where temporal envelope shaping is to be performed. Further, for example, when the encoding scheme of the second decoding unit is bandwidth extension in the time domain, a frequency band(s) to be decoded by the second decoding unit may be selected as the frequency band(s) where temporal envelope shaping is to be performed. For example, when the encoding scheme of the second decoding unit is bandwidth extension in the frequency domain, a frequency band(s) to be decoded by the second decoding unit may be selected as the frequency band(s) where temporal envelope shaping is to be performed. For example, a frequency band(s) where a signal is reproduced with another frequency band(s) by bandwidth extension may be selected as the frequency band(s) where temporal envelope shaping is to be performed. For example, a frequency band(s) where a signal is approximated by using a signal in another frequency band(s) by bandwidth extension may be selected as the frequency band(s) where temporal envelope shaping is to be performed. For example, a frequency band(s) where a pseudo-noise signal is generated by bandwidth extension may be selected as the frequency band(s) where temporal envelope shaping is to be performed. For example, a frequency band(s) excluding a frequency band(s) where a sinusoidal signal is added by bandwidth extension may be selected as the frequency band(s) where temporal envelope shaping is to be performed.

Further, in the case where the decoding unit10ahas the configuration described as the second example of the decoding unit10a, and the second encoding scheme is an encoding scheme that performs one or both of approximation of a transform coefficient(s) of a frequency band(s) or component(s) where the number of bits allocated by the first encoding scheme is smaller than a specified threshold (or a frequency band(s) or component(s) that is not encoded by the first encoding scheme) to a transform coefficient(s) in another frequency band(s) or component(s) and addition (or substitution) of a transform coefficient(s) of a pseudo-noise signal, a frequency band(s) or component where approximation of a transform coefficient(s) to a transform coefficient(s) in another frequency band(s) or component(s) is made may be selected as the frequency band(s) or component(s) where temporal envelope shaping is to be performed. For example, a frequency band(s) or component(s) where a transform coefficient(s) of a pseudo-noise signal is added or substituted may be selected as the frequency band(s) or component(s) where temporal envelope shaping is to be performed. For example, a frequency band(s) or component(s) may be selected as the frequency band(s) or component(s) where temporal envelope shaping is to be performed in accordance with an approximation method when approximating a transform coefficient(s) by using a transform coefficient(s) in another frequency band(s) or component(s). For example, in the case of using a method of whitening a transform coefficient(s) in another frequency band(s) or component(s) as the approximation method, the frequency band(s) or component(s) where temporal envelope shaping is to be performed may be selected according to the strength of the whitening. For example, in the case of adding (or substituting) a transform coefficient(s) of a pseudo-noise signal, the frequency band(s) or component(s) where temporal envelope shaping is to be performed may be selected according to the level of the pseudo-noise signal.

Furthermore, in the case where the decoding unit10ahas the configuration described as the second example of the decoding unit10a, and the second encoding scheme is an encoding scheme that generates a pseudo-noise signal or reproduces a signal in another frequency component (or makes approximation using a signal in another frequency component) for a frequency component that is quantized to zero by the first encoding scheme (that is, not encoded by the first encoding scheme), a frequency component where a pseudo-noise signal is generated may be selected as the frequency component where temporal envelope shaping is to be performed. For example, a frequency component where reproduction of a signal in another frequency component (or approximation using a signal in another frequency component) is done may be selected as the frequency component where temporal envelope shaping is to be performed. For example, in the case of reproducing a signal in another frequency component (or making approximation using a signal in another frequency component) for a certain frequency component, the frequency component where temporal envelope shaping is to be performed may be selected according to the frequency of a source component of the reproduction (or approximation). For example, the frequency component where temporal envelope shaping is to be performed may be selected according to whether or not to perform processing on a source frequency component of the reproduction during the reproduction. Further, for example, the frequency component where temporal envelope shaping is to be performed may be selected according to processing to be performed on a source frequency component of the reproduction (or approximation) during the reproduction (or approximation). For example, in the case where the processing to be performed on a source frequency component of the reproduction (or approximation) is whitening, the frequency component where temporal envelope shaping is to be performed may be selected according to the strength of the whitening. Further, for example, the frequency component where temporal envelope shaping is to be performed may be selected according to a method of approximation.

A method of selecting a frequency component or a frequency band(s) may be a combination of the above-described examples. Further, the frequency component(s) or band(s) of a frequency-domain decoded signal where temporal envelope shaping is to be performed may be selected by using at least one of the frequency-domain decoded signal and the decoding related information, and a method of selecting a frequency component or a frequency band(s) is not limited to the above examples.

The frequency selective temporal envelope shaping unit10bC shapes the temporal envelope of the frequency band(s) of the decoded signal which is selected by the frequency selection unit10bB into a desired temporal envelope (Step S10-2-3). The temporal envelope shaping may be done for each frequency component.

As a method for temporal envelope shaping, the temporal envelope may be made flat by filtering with a linear prediction inverse filter using a linear prediction coefficient(s) obtained by linear prediction analysis of a transform coefficient(s) of a selected frequency band(s), for example. A transfer function A(z) of the linear prediction inverse filter is a function that represents a response of the linear prediction inverse filter in a discrete-time system, which is represented by the following equation:

A⁡(z)=1+∑i=1pai⁢z-i(1)

where p is a prediction order and αi(i=1, . . . , p) is a linear prediction coefficient. For example, a method of making the temporal envelope rising or falling by filtering a transform coefficient(s) of a selected frequency band(s) with a linear prediction filter using the linear prediction coefficient(s) may be used. A transfer function of the linear prediction filter is represented by the following equation:

1A⁡(z)=11+∑i=1pai⁢z-i(2)

In the temporal envelope shaping using the linear prediction coefficient(s), the strength of making the temporal envelope flat, or rising or falling may be adjusted using a bandwidth expansion ratio ρ as the following equations.

A⁡(z)=1+∑i=1pai⁢ρi⁢z-i(3)1A⁡(z)=11+∑i=1pai⁢ρi⁢z-i(4)

The above-described example may be performed on a sub-sample at arbitrary time t of a sub-band signal that is obtained by transforming a decoded signal into a frequency-domain signal by a filter bank, not only on a transform coefficient(s) that is obtained by time-frequency transform of the decoded signal. In the above example, by filtering a decoded signal in the frequency domain on the basis of linear prediction analysis, the distribution of the power of the decoded signal in the time domain is changed to thereby shape the temporal envelope.

Further, for example, the temporal envelope may be flattened by converting the amplitude of a sub-band signal obtained by transforming a decoded signal into a frequency-domain signal by a filter bank into the average amplitude of a frequency component(s) (or frequency band(s)) where temporal envelope shaping is to be performed in an arbitrary time segment. It is thereby possible to make the temporal envelope flat while maintaining the energy of the frequency component(s) (or frequency band(s)) of the time segment before temporal envelope shaping. Likewise, the temporal envelope may be made rising or falling by changing the amplitude of a sub-band signal while maintaining the energy of the frequency component(s) (or frequency band(s)) of the time segment before temporal envelope shaping.

Further, for example, as shown inFIG.13, in a frequency band(s) that contains a frequency component(s) or frequency band(s) that is not selected as the frequency component(s) or frequency band(s) where temporal envelope shaping is to be performed by the frequency selection unit10bB (which is referred to as a non-selected frequency component(s) or non-selected frequency band(s)), temporal envelope shaping may be performed by the above-described temporal envelope shaping method after replacing a transform coefficient(s) (or sub-sample(s)) of the non-selected frequency component(s) (or non-selected frequency band(s)) of a decoded signal with another value, and then the transform coefficient(s) (or sub-sample(s)) of the non-selected frequency component(s) (or non-selected frequency band(s)) may be set back to the original value before the replacement, thereby performing temporal envelope shaping on the frequency component(s) (or frequency band(s)) excluding the non-selected frequency component(s) (or non-selected frequency band(s)).

In this way, even when the frequency component(s) (or frequency band(s)) where temporal envelope shaping is to be performed is divided into many small segments due to scattered non-selected frequency components (or non-selected frequency bands), it is possible to perform temporal envelope shaping of the frequency component(s) (or frequency band(s)) segments all together, thereby achieving reduction of computational complexity. For example, in the above-described temporal envelope shaping method using the linear prediction analysis, while it is required to perform the linear prediction analysis for each of the frequency component(s) (or frequency band(s)) segments where temporal envelope shaping is to be performed without this technique, it is only necessary to perform the linear prediction analysis once for the frequency component(s) (or frequency band(s)) segments including non-selected frequency components (or non-selected frequency bands), and further it is only necessary to perform filtering with the linear prediction inverse filter (or linear prediction filter) of the frequency component(s) (or frequency band(s)) segments including non-selected frequency components (or non-selected frequency bands) all at once, thereby achieving reduction of computational complexity.

In the replacement of a transform coefficient(s) (or sub-sample(s)) of the non-selected frequency component(s) (or non-selected frequency band(s)), the amplitude of a transform coefficient(s) (or sub-sample(s)) of the non-selected frequency component(s) (or non-selected frequency band(s)) may be replaced with the average value of the amplitude including the transform coefficient(s) (or sub-sample(s)) of the non-selected frequency component(s) (or non-selected frequency band(s)) and the adjacent frequency component(s) (or frequency band(s)). As this time, the sign of the transform coefficient(s) may be the same as the sign of the original transform coefficient(s), and the phase of the sub-sample may be the same as the phase of the original sub-sample. Furthermore, in the case where the transform coefficient(s) (or sub-sample(s)) of the frequency component(s) (or frequency band(s)) is not quantized/encoded, and it is selected to perform temporal envelope shaping on a frequency component(s) (or frequency band(s)) that is generated by reproduction or approximation using the transform coefficient(s) (or sub-sample(s)) of another frequency component(s) (or frequency band(s)), or/and generation or addition of a pseudo-noise signal, and/or addition of a sinusoidal signal, the transform coefficient(s) (or sub-sample(s)) of the non-selected frequency component(s) (or non-selected frequency band(s)) may be replaced with a transform coefficient(s) (or sub-sample(s)) that is generated by reproduction or approximation using the transform coefficient(s) (or sub-sample(s)) of another frequency component(s) (or frequency band(s)), or/and generation or addition of a pseudo-noise signal, and/or addition of a sinusoidal signal in a pseudo manner. A temporal envelope shaping method of the selected frequency band(s) may be a combination of the above-described methods, and the temporal envelope shaping method is not limited to the above examples.

The time-frequency inverse transform unit10bD transforms the decoded signal where temporal envelope shaping has been performed in a frequency selective manner into the signal in the time domain and outputs it (Step S10-2-4).

Second Embodiment

FIG.14is a view showing the configuration of an audio decoding device11according to a second embodiment. A communication device of the audio decoding device11receives an encoded sequence of an audio signal and outputs a decoded audio signal to the outside. As shown inFIG.14, the audio decoding device11functionally includes a demultiplexing unit11a, a decoding unit10a, and a selective temporal envelope shaping unit11b.

FIG.15is a flowchart showing the operation of the audio decoding device11according to the second embodiment.

The demultiplexing unit11adivides an encoded sequence into the encoded sequence to obtain a decoded signal and temporal envelope information by decoding/inverse quantization (Step S11-1). The decoding unit10adecodes the encoded sequence and thereby generates a decoded signal (Step S10-1). When the temporal envelope information is encoded or/and quantized, it is decoded or/and inversely quantized to obtain the temporal envelope information.

The temporal envelope information may be information indicating that the temporal envelope of an input signal that has been encoded by an encoding device is flat, for example. For example, it may be information indicating that the temporal envelope of the input signal is rising. For example, it may be information indicating that the temporal envelope of the input signal is falling.

Further, for example, the temporal envelope information may be information indicating the degree of flatness of the temporal envelope of the input signal, information indicating the degree of rising of the temporal envelope of the input signal, or information indicating the degree of falling of the temporal envelope of the input signal, for example.

Further, for example, the temporal envelope information may be information indicating whether or not to shape the temporal envelope by the selective temporal envelope shaping unit.

The selective temporal envelope shaping unit11breceives decoding related information, which is information obtained when decoding the encoded sequence, and the decoded signal from the decoding unit10a, receives the temporal envelope information from the demultiplexing unit, and selectively shapes the temporal envelope of the decoded signal component into a desired temporal envelope based on at least one of them (Step S11-2).

A method of the selective temporal envelope shaping in the selective temporal envelope shaping unit11bmay be the same as the one in the selective temporal envelope shaping unit10b, or the selective temporal envelope shaping may be performed by taking the temporal envelope information into consideration as well, for example. For example, in the case where the temporal envelope information is information indicating that the temporal envelope of an input signal that has been encoded by an encoding device is flat, the temporal envelope may be shaped to be flat based on this information. In the case where the temporal envelope information is information indicating that the temporal envelope of the input signal is rising, for example, the temporal envelope may be shaped to rise based on this information. In the case where the temporal envelope information is information indicating that the temporal envelope of the input signal is falling, for example, the temporal envelope may be shaped to fall based on this information.

Further, for example, in the case where the temporal envelope information is information indicating the degree of flatness of the temporal envelope of the input signal, the degree of making the temporal envelope flat may be adjusted based on this information. In the case where the temporal envelope information is information indicating the degree of rising of the temporal envelope of the input signal, for example, the degree of making the temporal envelope rising may be adjusted based on this information. In the case where the temporal envelope information is information indicating the degree of falling of the temporal envelope of the input signal, for example, the degree of making the temporal envelope falling may be adjusted based on this information.

Further, for example, in the case where the temporal envelope information is information indicating whether or not to shape the temporal envelope by the selective temporal envelope shaping unit11b, whether or not to perform temporal envelope shaping may be determined based on this information.

Further, for example, in the case of performing temporal envelope shaping based on the temporal envelope information of the above-described examples, a frequency component (or frequency band) where temporal envelope shaping is to be performed may be selected in the same way as in the first embodiment, and the temporal envelope of the selected frequency component(s) (or frequency band(s)) of the decoded signal may be shaped into a desired temporal envelope.

FIG.16is a view showing the configuration of an audio encoding device21according to the second embodiment. A communication device of the audio encoding device21receives an audio signal to be encoded from the outside, and outputs an encoded sequence to the outside. As shown inFIG.16, the audio encoding device21functionally includes an encoding unit21a, a temporal envelope information encoding unit21b, and a multiplexing unit21c.

FIG.17is a flowchart showing the operation of the audio encoding device21according to the second embodiment.

The encoding unit21aencodes an input audio signal and generates an encoded sequence (Step S21-1). The encoding scheme of the audio signal in the encoding unit21ais an encoding scheme corresponding to the decoding scheme of the decoding unit10adescribed above.

The temporal envelope information encoding unit21bgenerates temporal envelope information with use of the input audio signal and at least one of information obtained when encoding the audio signal in the encoding unit21a. The generated temporal envelope information may be encoded/quantized (Step S21-2). The temporal envelope information may be temporal envelope information that is obtained in the demultiplexing unit11aof the audio decoding device11.

Further, in the case where processing related to temporal envelope shaping, which is different from the processing in the present invention, is performed when generating a decoded signal in the decoding unit of the audio decoding device11, and information concerning this temporal envelope shaping processing is stored in the audio encoding device21, for example, the temporal envelope information may be generated using this information. For example, information as to whether or not to shape the temporal envelope in the selective temporal envelope shaping unit11bof the audio decoding device11may be generated based on information as to whether or not to perform temporal envelope shaping processing which is different from the one in the present invention.

Further, in the case where the selective temporal envelope shaping unit11bof the audio decoding device11performs the temporal envelope shaping using the linear prediction analysis that is described in the first example of the selective temporal envelope shaping unit10bof the audio decoding device10according to the first embodiment, for example, it may generate the temporal envelope information by using a result of the linear prediction analysis of a transform coefficient(s) (or sub-band samples) of an input audio signal, just like the linear prediction analysis in this temporal envelope shaping. To be specific, a prediction gain by the linear prediction analysis may be calculated, and the temporal envelope information may be generated based on the prediction gain. When calculating the prediction gain, linear prediction analysis may be performed on the transform coefficient(s) (or sub-band sample(s)) of the whole of the frequency band(s) of an input audio signal, or linear prediction analysis may be performed on the transform coefficient(s) (or sub-band sample(s)) of a part of the frequency band(s) of an input audio signal. Furthermore, an input audio signal may be divided into a plurality of frequency band segments, and linear prediction analysis of the transform coefficient(s) (or sub-band sample(s)) may be performed for each frequency band segment, and because a plurality of prediction gains are obtained in this case, the temporal envelope information may be generated by using the plurality of prediction gains.

Further, for example, information obtained when encoding the audio signal in the encoding unit21amay be at least one of information obtained when encoding by the encoding scheme corresponding to the first decoding scheme (first encoding scheme) and information obtained when encoding by the encoding scheme corresponding to the second decoding scheme (second encoding scheme) in the case where the decoding unit10ahas the configuration of the second example.

The multiplexing unit21cmultiplexes the encoded sequence obtained by the encoding unit and the temporal envelope information obtained by the temporal envelope information encoding unit and outputs them (Step S21-3).

Third Embodiment

FIG.18is a view showing the configuration of an audio decoding device12according to a third embodiment. A communication device of the audio decoding device12receives an encoded sequence of an audio signal and outputs a decoded audio signal to the outside. As shown inFIG.18, the audio decoding device12functionally includes a decoding unit10aand a temporal envelope shaping unit12a.

FIG.19is a flowchart showing the operation of the audio decoding device12according to the third embodiment. The decoding unit10adecodes an encoded sequence and generates a decoded signal (Step S10-1). Then, the temporal envelope shaping unit12ashapes the temporal envelope of the decoded signal that is output from the decoding unit10ainto a desired temporal envelope (Step S12-1). For temporal envelope shaping, a method that makes the temporal envelope flat by filtering with the linear prediction inverse filter using a linear prediction coefficient(s) obtained by linear prediction analysis of a transform coefficient(s) of a decoded signal, or a method that makes the temporal envelope rising or falling by filtering with the linear prediction filter using the linear prediction coefficient(s) may be used, as described in the first embodiment. Further, the strength of making the temporal envelope flat, rising or falling may be adjusted using a bandwidth expansion ratio, or the temporal envelope shaping in the above-described example may be performed on a sub-sample(s) at arbitrary time t of a sub-band signal obtained by transforming a decoded signal into a frequency-domain signal by a filter bank, instead of a transform coefficient(s) of the decoded signal. Furthermore, as described in the first embodiment, the amplitude of the sub-band signal may be corrected to achieve a desired temporal envelope in an arbitrary time segment, and, for example, the temporal envelope may be flattened by changing the amplitude of the sub-band signal into the average amplitude of a frequency component(s) (or frequency band(s)) where temporal envelope shaping is to be performed. The above-described temporal envelope shaping may be performed on the entire frequency band of the decoded signal, or may be performed on a specified frequency band(s).

Fourth Embodiment

FIG.20is a view showing the configuration of an audio decoding device13according to a fourth embodiment. A communication device of the audio decoding device13receives an encoded sequence of an audio signal and outputs a decoded audio signal to the outside. As shown inFIG.20, the audio decoding device13functionally includes a demultiplexing unit11a, a decoding unit10a, and a temporal envelope shaping unit13a.

FIG.21is a flowchart showing the operation of the audio decoding device13according to the fourth embodiment. The demultiplexing unit11adivides an encoded sequence into the encoded sequence to obtain a decoded signal and temporal envelope information by decoding/inverse quantization (Step S11-1). The decoding unit10adecodes the encoded sequence and thereby generates a decoded signal (Step S10-1). The temporal envelope shaping unit13areceives the temporal envelope information from the demultiplexing unit11a, and shapes the temporal envelope of the decoded signal that is output from the decoding unit10ainto a desired temporal envelope based on the temporal envelope information (Step S13-1).

The temporal envelope information may be information indicating that the temporal envelope of an input signal that has been encoded by an encoding device is flat, information indicating that the temporal envelope of the input signal is rising, or information indicating that the temporal envelope of the input signal is falling, as described in the second embodiment. Further, for example, the temporal envelope information may be information indicating the degree of flatness of the temporal envelope of the input signal, information indicating the degree of rising of the temporal envelope of the input signal, information indicating the degree of falling of the temporal envelope of the input signal, or information indicating whether or not to shape the temporal envelope in the temporal envelope shaping unit13a.

[Hardware Configuration]

Each of the above-described audio decoding devices10,11,12,13and the audio encoding device21is composed of hardware such as CPU.FIG.11is a view showing an example of hardware configurations of the audio decoding devices10,11,12,13and the audio encoding device21. As shown inFIG.11, each of the audio decoding devices10,11,12,13and the audio encoding device21is physically configured as a computer system including a CPU100, a RAM101and a ROM102as a main storage device, an input/output device103such as a display, a communication module104, an auxiliary storage device105and the like.

The functions of each functional block of the audio decoding devices10,11,12,13and the audio encoding device21are implemented by loading given computer software onto hardware such as the CPU100, the RAM101or the like shown inFIG.22, making the input/output device103, the communication module104and the auxiliary storage device105operate under control of the CPU100, and performing data reading and writing in the RAM101.

[Program Structure]

An audio decoding program50and an audio encoding program60that cause a computer to execute processing by the above-described audio decoding devices10,11,12,13and the audio encoding device21, respectively, are described hereinafter.

As shown inFIG.23, the audio decoding program50is stored in a program storage area41formed in a recording medium40that is inserted into a computer and accessed, or included in a computer. To be specific, the audio decoding program50is stored in the program storage area41formed in the recording medium40that is included in the audio decoding device10.

The functions implemented by executing a decoding module50aand a selective temporal envelope shaping module50bof the audio decoding program50are the same as the functions of the decoding unit10aand the selective temporal envelope shaping unit10bof the audio decoding device10described above, respectively. Further, the decoding module50aincludes modules for serving as the decoding/inverse quantization unit10aA, the decoding related information output unit10aB and the time-frequency inverse transform unit10aC. Further, the decoding module50amay include modules for serving as the encoded sequence analysis unit10aD, the first decoding unit10aE and the second decoding unit10aF.

Further, the selective temporal envelope shaping module50bincludes modules for serving as the time-frequency transform unit10bA, the frequency selection unit10bB, the frequency selective temporal envelope shaping unit10bC and the time-frequency inverse transform unit10bD.

Further, in order to serve as the above-described audio decoding device11, the audio decoding program50includes modules for serving as the demultiplexing unit11a, the decoding unit10aand the selective temporal envelope shaping unit11b.

Further, in order to serve as the above-described audio decoding device12, the audio decoding program50includes modules for serving as the decoding unit10aand the temporal envelope shaping unit12a.

Further, in order to serve as the above-described audio decoding device13, the audio decoding program50includes modules for serving as the demultiplexing unit11a, the decoding unit10aand the temporal envelope shaping unit13a.

Further, as shown inFIG.24, the audio encoding program60is stored in a program storage area41formed in a recording medium40that is inserted into a computer and accessed, or included in a computer. To be specific, the audio encoding program60is stored in the program storage area41formed in the recording medium40that is included in the audio encoding device20.

The audio encoding program60includes an encoding module60a, a temporal envelope information encoding module60b, and a multiplexing module60c. The functions implemented by executing the encoding module60a, the temporal envelope information encoding module60band the multiplexing module60care the same as the functions of the encoding unit21a, the temporal envelope information encoding unit21band the multiplexing unit21cof the audio encoding device21described above, respectively.

Note that a part or the whole of each of the audio decoding program50and the audio encoding program60may be transmitted through a transmission medium such as a communication line, received and recorded (including being installed) by another device. Further, each module of the audio decoding program50and the audio encoding program60may be installed not in one computer but in any of a plurality of computers. In this case, the processing of each of the audio decoding program50and the audio encoding program60is performed by a computer system composed of the plurality of computers.

REFERENCE SIGNS LIST

10aF-1inverse quantization unit10audio decoding device10adecoding unit10aA decoding/inverse quantization unit10aB decoding related information output unit10aC time-frequency inverse transform unit10aD encoded sequence analysis unit10aE first decoding unit10aE-a first decoding/inverse quantization unit10aE-b first decoding related information output unit10aF second decoding unit10aF-a second decoding/inverse quantization unit10aF-b second decoding related information output unit10aF-c decoded signal synthesis unit10bselective temporal envelope shaping unit10bA time-frequency transform unit10bB frequency selection unit10bC frequency selective temporal envelope shaping unit10bD time-frequency inverse transform unit11audio decoding device11ademultiplexing unit11bselective temporal envelope shaping unit12audio decoding device12atemporal envelope shaping unit13audio decoding device13atemporal envelope shaping unit21audio encoding device21aencoding unit21btemporal envelope information encoding unit21cmultiplexing unit