Spectral smoothing device, encoding device, decoding device, communication terminal device, base station device, and spectral smoothing method
Disclosed is a spectral smoothing device with a structure whereby smoothing is performed after a nonlinear conversion has been performed for a spectrum calculated from an audio signal, and with which the amount of processing calculation is significantly reduced while maintaining excellent audio quality. With this spectral smoothing device, a sub band division unit ( 102 ) divides an input spectrum into multiple sub bands; a representative value calculation unit ( 103 ) calculates a representative value for each sub band using an arithmetic mean and a geometric mean; with respect to each representative value, a nonlinear conversion unit ( 104 ) performs a nonlinear conversion the characteristic of which is further emphasized as the value increases; and a smoothing unit ( 105 ) that smoothes the representative value which has undergone the nonlinear conversion for each sub band, at the frequency domain.
1. A spectrum smoothing apparatus comprising:
a time-frequency transformation section that performs a time-frequency transformation of an input signal and generates a frequency component;
a subband dividing section that divides the frequency component into a plurality of subbands;
a representative value calculating section that calculates, for each subband, a representative value by calculating an arithmetic mean and by using a multiplication calculation using the arithmetic mean;
a non-linear transformation section that performs a non-linear transformation of representative values of the subbands; and
a smoothing section that smoothes the representative values subjected to the non-linear transformation in the frequency domain, wherein the representative value calculating section calculates the representative values of the subbands by dividing each subband into a plurality of subgroups, calculating an arithmetic mean value per subgroup, and calculating, for each subband, the geometric mean of the arithmetic mean values of the subgroups corresponding to the subband as the representative value of the subband.
2. The spectrum smoothing apparatus according to claim 1 , further comprising an inverse non-linear transformation section that performs an inverse non-linear transformation of an opposite characteristic to the non-linear transformation, for the smoothed representative values.
3. The spectrum smoothing apparatus according to claim 1 , wherein the non-linear transformation section performs the non-linear transformation having a characteristic of emphasizing a greater value, for the representative values.
4. The spectrum smoothing apparatus according to claim 1 , wherein the non-linear transformation section performs a logarithmic transform as the non-linear transformation.
5. The spectrum smoothing apparatus according to claim 1 , wherein the representative value calculating section calculates the representative values of the subbands by estimating a geometric mean using a result of the multiplication calculation.
6. A spectrum smoothing apparatus comprising:
a time-frequency transformation section that performs a time-frequency transformation of an input signal and generates a frequency component;
a subband dividing section that divides the frequency component into a plurality of subbands;
a representative value calculating section that calculates, for each subband, a representative value by calculating an arithmetic mean and by using a multiplication calculation using the arithmetic mean;
a non-linear transformation section that performs a non-linear transformation of representative values of the subbands; and
a smoothing section that smoothes the representative values subjected to the non-linear transformation in the frequency domain, wherein:
the representative value calculating section calculates the representative values of each subband by dividing each subband into a plurality of subgroups, calculating an arithmetic mean value of each subgroup, and calculates, for each subband, a value obtained by multiplying arithmetic means values of subgroups corresponding to the subband as the representative value of the subband; and
the non-linear transformation section calculates an intermediate value of each subband by performing the non-linear transformation of the representative value of each subband and calculates a value obtained by multiplying the intermediate in each subband by a reciprocal of a number of subgroups in each subband as a representative value subjected to the smoothing section.
7. A coding apparatus comprising:
a first coding section that generates first coded information by encoding a lower band part of an input signal at or below a predetermined frequency;
a decoding section that generates a decoded signal by decoding the first coded information; and
a second coding section that generates second coded information by dividing a higher band part of the input signal above the predetermined frequency into a plurality of subbands and estimating the plurality of subbands from the input signal or the decoded signal,
wherein the second coding section comprises a spectrum smoothing apparatus according to claim 1 that receives as input and smoothes the decoded signal, and estimates the plurality of subbands from the input signal or the smoothed decoded signal.
8. A decoding apparatus comprising:
a receiving section that receives first coded information and second coded information, the first coded information being obtained by encoding a lower band part of a coding side input signal at or below a predetermined frequency, and the second coded information being generated by dividing a higher band part of the coding side input signal above the predetermined frequency into a plurality of subbands and estimating the plurality of subbands from a first decoded signal obtained by decoding the coding side input signal or the first coded information;
a first decoding section that decodes the first coded information and generates a second decoded signal; and
a second decoding section that generates a third decoded signal by estimating a higher band part of the coding side input signal using the second coded information,
wherein the second decoding section comprises the spectrum smoothing apparatus of claim 1 that receives as input and smoothes the second decoded signal and estimates the higher band part of the coding side input signal from the smoothed second decoded signal.
9. A communication terminal apparatus comprising the spectrum smoothing apparatus of claim 1 .
10. A base station apparatus comprising the spectrum smoothing apparatus of claim 1 .
11. A communication terminal apparatus comprising the spectrum smoothing apparatus of claim 6 .
12. A base station apparatus comprising the spectrum smoothing apparatus of claim 6 .