Decoding device, encoding device, decoding method, and encoding method

1. A decoding device, comprising:

a separator that separates first encoded data, where a spectrum including a low-band spectrum of audio signals has been encoded, and second encoded data where a high-band spectrum of a higher band than the low-band spectrum has been encoded, based on the first encoded data;

a first decoder that decodes the first encoded data and generates a first decoded spectrum;

a first amplitude normalizer that divides the amplitude of the first decoded spectrum into a plurality of sub-bands, normalizes the spectrum of each sub-band by the largest value of the amplitude of the first decoded spectrum within each sub-band, and generates a normalized spectrum;

a noise amplitude adjuster that adjusts an amplitude of a normalized noise spectrum obtained by normalizing a noise spectrum, in accordance with at least one of sparse information indicating a degree of sparseness of the first decoded spectrum, and sparse information indicating a degree of sparseness of the normalized spectrum, wherein the noise amplitude adjuster performs adjustment based on a threshold value, the threshold value being calculated using the normalized spectrum or sparse information of the first decoded spectrum;

an adder that adds an adjusted normalized noise spectrum to the normalized spectrum and generates a noise-added normalized spectrum;

a second decoder that decodes the second encoded data using the noise-added normalized spectrum, and generates a second noise-added spectrum; and

a converter that performs frequency-time conversion regarding a spectrum generated by concatenating a spectrum based on the first decoded spectrum and a spectrum based on the second noise-added spectrum.

2. The decoding device according to claim 1 ,

wherein the converter performs frequency-time conversion regarding a spectrum generated by concatenating a spectrum based on a first noise-added decoded spectrum obtained by adding the adjusted normalized noise spectrum to the first decoded spectrum, and the second noise-added spectrum.

3. The decoding device according to claim 1 ,

wherein an amplitude of the adjusted normalized noise spectrum is based on at least one of bit allocation information of the first decoded spectrum, and sparse information indicating a degree of sparseness of the first decoded spectrum.

4. The decoding device according to claim 1 ,

wherein the noise amplitude adjuster adjusts an amplitude of the normalized noise spectrum so that a largest value of the normalized noise spectrum is equal to or smaller than the threshold value, and

wherein an amplitude adjuster adjusts an amplitude of the normalized spectrum regarding a non-zero content of the normalized spectrum by removing the non-zero content smaller than the threshold value, or

wherein the noise amplitude adjuster adjusts an amplitude of the normalized noise spectrum using scaling a maximum amplitude of the normalized noise spectrum using the threshold, and

wherein the amplitude adjuster adjusts the first decoded spectrum or the normalized spectrum by removing a low amplitude using the threshold.

5. The decoding device according to claim 4 ,

wherein the amplitude adjuster zeroes the non-zero content of the normalized spectrum based on a zeroing threshold value to obtain a zero content separated from the non-zero content of the normalized spectrum, the zeroing threshold value being calculated using the threshold value.

6. The decoding device according to claim 5 , further comprising:

a noise adder that adds the adjusted normalized noise spectrum to a position of the zero content that has been zeroed.

7. The decoding device according to claim 1 , further comprising:

an amplitude readjuster that applies a smoothing process on a noise component of the second noise-added spectrum.

8. The decoding device according to claim 7 , wherein the amplitude readjuster

smoothens an energy change between frames of the second noise-added spectrum using a energy of the noise component of the second noise-added spectrum calculated based on a threshold value, and

adjusts an amplitude of the noise component of the second noise-added spectrum using a scaling coefficient representing a ratio between a noise component energy of the noise component of the second noise-added spectrum and an energy of the noise component of the second noise-added spectrum to be obtained after smoothing.

9. A decoding method, comprising:

separating first encoded data, where a spectrum including a low-band spectrum of audio signals has been encoded, and second encoded data where a high-band spectrum of a higher band than the low-band spectrum has been encoded, based on the first encoded data;

decoding the first encoded data and generating a first decoded spectrum;

dividing the amplitude of the first decoded spectrum into a plurality of sub-bands, normalizing the spectrum of each sub-band by the largest value of the amplitude of the first decoded spectrum within each sub-band, and generating a normalized spectrum;

adjusting an amplitude of a normalized noise spectrum obtained by normalizing a noise spectrum, in accordance with at least one of sparse information indicating a degree of sparseness of the first decoded spectrum, and sparse information indicating a degree of sparseness of the normalized spectrum, wherein the adjusting the amplitude comprises using a threshold value, the threshold value being calculated using the normalized spectrum or sparse information of the first decoded spectrum;

adding an adjusted normalized noise spectrum to the normalized spectrum and generating a noise-added normalized spectrum;

decoding the second encoded data using the noise-added normalized spectrum, and generating a second noise-added spectrum; and

performing frequency-time conversion regarding a spectrum generated by concatenating a spectrum based on the first decoded spectrum and a spectrum based on the second noise-added spectrum.

10. The decoding method according to claim 9 ,

wherein frequency-time conversion is performed regarding a spectrum generated by concatenating a spectrum based on a first noise-added decoded spectrum obtained by adding the adjusted normalized noise spectrum to the first decoded spectrum, and the second noise-added spectrum.

11. The decoding method according to claim 9 ,

wherein the amplitude of the adjusted normalized noise spectrum is based on at least one of bit allocation information of the first decoded spectrum, and sparse information indicating a degree of sparseness of the first decoded spectrum.

12. The decoding method according to claim 9 ,

wherein an amplitude of the normalized noise spectrum is adjusted so that a largest value of the normalized noise spectrum is equal to or smaller than the threshold value, and

wherein an amplitude of the normalized spectrum is adjusted regarding a non-zero content of the normalized spectrum by removing the non-zero content smaller than the threshold value, or

wherein an amplitude of the normalized noise spectrum is adjusted using scaling a maximum amplitude of the normalized noise spectrum using the threshold value, and

wherein the first decoded spectrum or the normalized spectrum is adjusted by removing a low amplitude using the threshold value.

13. The decoding method according to claim 12 ,

wherein a zero content of the normalized spectrum is obtained by zeroing based on a zeroing threshold value to separate the zero content and a non-zero content of the normalized spectrum, the zeroing threshold value being calculated using the threshold value.

14. The decoding method according to claim 13 , further comprising:

adding the adjusted normalized noise spectrum to a position of the zero content that has been zeroed.

15. The decoding method according to claim 9 , further comprising:

applying a smoothing process on a noise component of the second noise-added spectrum.

16. The decoding method according to claim 15 ,

wherein an energy change is smoothened between frames of the second noise-added spectrum using an energy of the noise component of the second noise-added spectrum calculated based on a threshold value, and

wherein an amplitude of the noise component of the second noise-added spectrum is adjusted using a scaling coefficient representing a ratio between a noise component energy of the noise component of the second noise-added spectrum and an energy of the noise component of the second noise-added spectrum to be obtained after smoothing.

17. A non-transitory storage medium having stored thereon a computer program for performing, when running on a computer, a method of claim 9 .

18. A decoding device, comprising:

a separator that separates first encoded data, where a spectrum including a low-band spectrum of audio signals has been encoded, and second encoded data where a high-band spectrum of a higher band than the low-band spectrum has been encoded, based on the first encoded data;

a first decoder that decodes the first encoded data and generates a first decoded spectrum;

a first amplitude normalizer that divides the amplitude of the first decoded spectrum into a plurality of sub-bands, normalizes the spectrum of each sub-band by the largest value of the amplitude of the first decoded spectrum within each sub-band, and generates a normalized spectrum;

an adder that adds a noise spectrum to the normalized spectrum and generates a noise-added normalized spectrum;

a second decoder that decodes the second encoded data using the noise-added normalized spectrum, and generates a second noise-added spectrum;

a converter that performs frequency-time conversion regarding a spectrum generated by concatenating a spectrum based on the first decoded spectrum and a spectrum based on the second noise-added spectrum; and

an amplitude readjuster that applies a smoothing process on a noise component of the second noise-added spectrum, wherein the amplitude readjuster

smoothens an energy change between frames of the second noise-added spectrum using an energy of the noise component of the second noise-added spectrum calculated based on a threshold value, and

adjusts an amplitude of the noise component of the second noise-added spectrum using a scaling coefficient representing a ratio between a noise component energy of the noise component of the second noise-added spectrum and an energy of the noise component of the second noise-added spectrum to be obtained after smoothing.

19. A decoding method, comprising:

separating first encoded data, where a spectrum including a low-band spectrum of audio signals has been encoded, and second encoded data where a high-band spectrum of a higher band than the low-band spectrum has been encoded, based on the first encoded data;

decoding the first encoded data and generating a first decoded spectrum;

dividing the amplitude of the first decoded spectrum into a plurality of sub-bands, normalizing the spectrum of each sub-band by the largest value of the amplitude of the first decoded spectrum within each sub-band, and generating a normalized spectrum;

adding a noise spectrum to the normalized spectrum and generating a noise-added normalized spectrum;

decoding the second encoded data using the noise-added normalized spectrum, and generating a second noise-added spectrum;

performing frequency-time conversion regarding a spectrum generated by concatenating a spectrum based on the first decoded spectrum and a spectrum based on the second noise-added spectrum;

applying a smoothing process on a noise component of a second noise-added spectrum, the applying comprising:

smoothing an energy change between frames of the second noise-added spectrum using an energy of a noise component of the second noise-added spectrum calculated based on a threshold value, and

adjusting an amplitude of the noise component of the second noise-added spectrum using a scaling coefficient representing a ratio between a noise component energy of the noise component of the second noise-added spectrum and an energy of the noise component of the second noise-added spectrum to be obtained after smoothing.

20. A non-transitory storage medium having stored thereon a computer program for performing, when running on a computer, a method of claim 19 .