Encoder, decoder, and method therefor

1. An encoding apparatus comprising:

a first encoder structured to generate first encoded information by encoding a lower frequency part of an input signal equal to or lower than a predetermined frequency;

a decoder structured to generate a decoded signal by decoding the first encoded information; and

a second encoder structured to generate second encoded information by dividing a high frequency part of the input signal higher than the predetermined frequency into a plurality of sub-bands, estimating the plurality of sub-bands respectively from the decoded signal, selecting a spectrum component within each of the sub-bands, and calculating a second amplitude adjustment parameter for adjusting an amplitude for the selected spectrum component, the second amplitude adjustment parameter being a correlation value of the selected spectrum component and the input signal in a logarithmic domain,

wherein the second encoder comprises:

a similar part searcher structured to search for a band which is most similar to a spectrum of each of the plurality of sub-bands and a first amplitude adjustment parameter from a spectrum of the decoded signal;

an amplitude value searcher structured to search for, for each of the sub-bands, a spectrum component having a maximum amplitude value for a spectrum of a high frequency that is estimated by the most similar band and the first amplitude adjustment parameter;

a spectrum component selector structured to select a spectrum component that is present in a region that has a wider bandwidth than a bandwidth of the spectrum component having the maximum amplitude value, the spectrum component having the maximum amplitude value being located at the center of the region; and

an amplitude adjustment parameter calculator structured to calculate the second amplitude adjustment parameter that is the correlation value of the selected spectrum component and the input signal in a logarithmic domain, for the selected spectrum component.

2. The encoding apparatus according to claim 1 , wherein the second encoder comprises:

a divider structured to divide the high frequency part of the input signal into P (P is an integer larger than 1) sub-bands, and obtains respective start positions and bandwidths of the P sub-bands as band division information;

a filter structured to filter the decoded signal, and generate P p-th (p=1, 2, . . . , P) estimated signals from a first estimated signal to a P-th estimated signal;

a setter structured to set pitch coefficients to be used by the filter, by changing the pitch coefficients;

a searcher structured to search for a pitch coefficient that makes a highest degree of similarity between the p-th estimated signal and a p-th sub-band out of the pitch coefficients, as a p-th optimal pitch coefficient; and

a multiplexer structured to obtain the second encoded information by multiplexing P optimal pitch coefficients from a first optimal pitch coefficient to a P-th optimal pitch coefficient with the band division information, wherein:

the setter is configured to set pitch coefficients to be used by the filter to estimate a first sub-band, by changing the pitch coefficient within a predetermined range, and set pitch coefficients to be used by the filter to estimate an m-th (m=2, 3, . . . , P) sub-band at and after a second sub-band, by changing the pitch coefficient within a range corresponding to an (m−1)-th optimal pitch coefficient, or within a predetermined range.

3. The encoding apparatus according to claim 1 , wherein the spectrum component selector is structured to select a spectrum component that is present in the region that has the predetermined threshold frequency band of a broader range for a sub-band in a higher frequency among the plurality of sub-bands.

4. A communication terminal device comprising the encoding apparatus according to claim 1 .

5. A base station apparatus comprising the encoding apparatus according to claim 1 .

6. The encoding apparatus according to claim 1 , wherein the spectrum component selector selects a spectrum component that has an even-numbered sample index, the sample index being assigned to each spectrum component.

7. A decoding apparatus comprising:

a receiver structured to receive first encoded information obtained by encoding a lower frequency part of an input signal equal to or lower than a predetermined frequency generated by an encoding apparatus, and second encoded information generated by dividing a high frequency part of the input signal higher than the predetermined frequency into a plurality of sub-bands, estimating the plurality of sub-bands respectively from a first decoded signal obtained by decoding the first encoded information, selecting a spectrum component within each of the sub-bands, and calculating a second amplitude adjustment parameter for adjusting an amplitude for the selected spectrum component, the second amplitude adjustment parameter being a correlation value of the selected spectrum component and the input signal in a logarithmic domain;

a first decoder structured to generate a second decoded signal by decoding the first encoded information; and

a second decoder structured to generate a third decoded signal by estimating a high frequency part of the input signal from the second decoded signal,

wherein the second encoded information is generated by searching for a band which is most similar to a spectrum of each of the plurality of sub-bands and a first amplitude adjustment parameter from a spectrum of the decoded signal, searching for, for each of the sub-bands, a spectrum component having a maximum amplitude value for a spectrum of a high frequency that is estimated by the most similar band and the first amplitude adjustment parameter, selecting a spectrum component that is present in a region that has a wider bandwidth than a bandwidth of the spectrum component having the maximum amplitude value, the spectrum component having the maximum amplitude value being located at the center of the region, and calculating the second amplitude adjustment parameter that is the correlation value of the selected spectrum component and the input signal in a logarithmic domain, for the selected spectrum component.

8. The decoding apparatus according to claim 7 , wherein the second decoder comprises:

an amplitude value searcher structured to search for, for each of the sub-bands, a spectrum component having a maximum amplitude value, for a band that is most similar to respective spectrums of the plurality of sub-bands calculated from the spectrum of the second decoded signal and for a spectrum of a high frequency that is estimated by a first amplitude adjustment parameter contained in the second encoded information;

a spectrum component selector structured to select a spectrum component that is present in a region that has a wider bandwidth than a bandwidth of the spectrum component having the maximum amplitude value, the spectrum component having the maximum amplitude value being located at the center of the region; and

an amplitude adjustment parameter applier structured to apply the second amplitude adjustment parameter that is the correlation value of the selected spectrum component and the input signal in a logarithmic domain, for the selected spectrum component.

9. The decoding apparatus according to claim 8 , wherein the amplitude value searcher structured to search for, for each of the sub-bands, a spectrum component having a maximum amplitude value, for a part of a spectrum component out of the spectrum of a high frequency that is estimated.

10. A communication terminal device comprising the decoding apparatus according to claim 7 .

11. A base station apparatus comprising the decoding apparatus according to claim 7 .

12. An encoding method comprising:

generating, by a processor, first encoded information by encoding a lower frequency part of an input signal equal to or lower than a predetermined frequency;

generating a decoded signal by decoding the first encoded information; and

generating a second encoded information by dividing a high frequency part of the input signal higher than the predetermined frequency into a plurality of sub-bands, estimating the plurality of sub-bands respectively from the decoded signal, selecting a spectrum component within each of the sub-bands, and calculating a second amplitude adjustment parameter for adjusting an amplitude for the selected spectrum component, the second amplitude adjustment parameter being a correlation value of the selected spectrum component and the input signal in a logarithmic domain,

wherein the generating of the second encoded information comprises:

searching for a band which is most similar to a spectrum of each of the plurality of sub-bands and a first amplitude adjustment parameter from a spectrum of the decoded signal;

searching for, for each of the sub-bands, a spectrum component having a maximum amplitude value for a spectrum of a high frequency that is estimated by the most similar band and the first amplitude adjustment parameter;

selecting a spectrum component that is present in a region that has a wider bandwidth than a bandwidth of the spectrum component having the maximum amplitude value, the spectrum component having the maximum amplitude value being located at the center of the region; and

calculating the second amplitude adjustment parameter that is the correlation value of the selected spectrum component and the input signal in a logarithmic domain, for the selected spectrum component.

13. A decoding method comprising:

receiving, by a processor, first encoded information obtained by encoding a lower frequency part of an input signal equal to or lower than a predetermined frequency generated by an encoding apparatus, and second encoded information generated by dividing a high frequency part of the input signal higher than the predetermined frequency into a plurality of sub-bands, estimating the plurality of sub-bands respectively from a first decoded signal obtained by decoding the first encoded information, selecting a spectrum component within each of the sub-bands, and calculating a second amplitude adjustment parameter for adjusting an amplitude for the selected spectrum component, the second amplitude adjustment parameter being a correlation value of the selected spectrum component and the input signal in a logarithmic domain;

generating a second decoded signal by decoding the first encoded information; and

generating a third decoded signal by estimating a high frequency part of the input signal from the second decoded signal,

wherein the second encoded information is generated by searching for a band which is most similar to a spectrum of each of the plurality of sub-bands and a first amplitude adjustment parameter from a spectrum of the decoded signal, searching for, for each of the sub-bands, a spectrum component having a maximum amplitude value for a spectrum of a high frequency that is estimated by the most similar band and the first amplitude adjustment parameter, selecting a spectrum component that is present in a region that has a wider bandwidth than a bandwidth of the spectrum component having the maximum amplitude value the spectrum component having the maximum amplitude value being located at the center of the region, and calculating the second amplitude adjustment parameter that is the correlation value of the selected spectrum component and the input signal in a logarithmic domain, for the selected spectrum component.