ENCODING METHOD, DECODING METHOD, ENCODER APPARATUS, DECODER APPARATUS, PROGRAM AND RECORDING MEDIUM

• US 20120265525A1
• Filed: 01/07/2011
• Published: 10/18/2012
• Est. Priority Date: 01/08/2010
• Status: Active Grant

• Current Assignee: Nippon Telegraph and Telephone Corporation
• Original Assignee: Nippon Telegraph and Telephone Corporation
• Inventors: Moriya, Takehiro, Harada, Noboru, Kamamoto, Yutaka
• Granted Patent: US 9,812,141 B2
• Time in Patent Office: Days
• US Class Current: 704/211
• CPC Class Codes: G10L 19/032 Quantisation or dequantisation of spectral components
• CPC Class Codes: G10L 19/09 Long term prediction, i.e. removing periodical redundancies, e.g. by using adaptive codebook or pitch predictor

Abstract

In encoding, pitch periods for time series signals in a predetermined time interval are calculated, and a code corresponding thereto is output. In that encoding, the resolutions for expressing the pitch periods and/or a pitch period encoding mode are switched according to whether an index indicating a periodicity and/or stationarity level of the time series signals satisfies a condition indicating high or low in periodicity and/or stationarity. In that decoding, according to whether an index indicating a periodicity and/or stationarity level, the index being included in or obtained from an input code corresponding to the predetermined time interval, satisfies a condition indicating high periodicity and/or stationarity, a decoding mode for a code, included in the input code, corresponding to pitch periods is switched to decode the code corresponding to the pitch periods to obtain the pitch periods corresponding to the predetermined time interval.

Claims

1. An encoding method comprising:

(A) a step of obtaining pitch periods corresponding to time series signals included in a predetermined time interval; and

(B) a step of outputting a code corresponding to the pitch periods;

wherein resolutions used to express the pitch periods and/or a pitch period encoding mode are switched according to whether an index that indicates a level of periodicity and/or stationarity of the time series signals satisfies a condition that indicates high periodicity and/or high stationarity or a condition that indicates low periodicity and/or low stationarity.

2. The encoding method according to claim 1,

wherein the step (B) comprises a step of outputting a code obtained by encoding the pitch periods expressed at a first resolution in each first time interval when the index does not satisfy the condition that indicates high periodicity and/or high stationarity, and

of outputting a code obtained by encoding the pitch periods expressed at a second resolution in each second time interval when the index satisfies the condition that indicates high periodicity and/or high stationarity;

and

the second resolution is higher than the first resolution and/or the second time interval is shorter than the first time interval.

3. The encoding method according to claim 1,

wherein the step (B) comprises a step of outputting a code corresponding to the pitch periods, obtained by encoding a pitch period in a first predetermined time interval included in the predetermined time interval and by variable-length encoding the difference between a value corresponding to a pitch period in a second predetermined time interval included in the predetermined time interval other than the first predetermined time interval and a value corresponding to a pitch period in a time interval other than the second predetermined time interval, when the index satisfies the condition that indicates high periodicity and/or high stationarity.

4. The encoding method according to claim 1,

wherein the step (B) comprises a step of outputting a code corresponding to the pitch periods, obtained by encoding a pitch period in a first predetermined time interval included in the predetermined time interval and by variable-length encoding information obtained by integrating the difference between a value corresponding to each pitch period in a plurality of second predetermined time intervals included in the predetermined time interval other than the first predetermined time interval and a value corresponding to each pitch period in time intervals other than the second predetermined time intervals, when the index satisfies the condition that indicates high periodicity and/or high stationarity.

5. The encoding method according to one of claims 1 to 4,

wherein the step (A) further comprises a step of obtaining a quantized pitch gain corresponding to the time series signals;

the index includes the quantized pitch gain or a value corresponding thereto; and

the condition that indicates high periodicity and/or high stationarity includes a condition in which the quantized pitch gain or the value corresponding thereto is larger than a specified value.

6. The encoding method according to one of claims 1 to 4,

wherein the step (A) further comprises a step of obtaining a vector-quantized gain code corresponding to a combination of a quantized pitch gain corresponding to the time series signals or a value corresponding to the quantized pitch gain, and a quantized fixed-codebook gain corresponding to the time series signals or a value corresponding to the quantized fixed-codebook gain;

the index includes the vector-quantized gain code; and

the condition that indicates high periodicity and/or high stationarity includes a condition in which the vector-quantized gain code corresponds to a combination of a quantized pitch gain that is larger than a specified value or a value that corresponds to the quantized pitch gain and that is larger than the specified value, and the quantized fixed-codebook gain or the value corresponding thereto.

7. The encoding method according to one of claims 1 to 4,

wherein the step (A) further comprises a step of obtaining a quantized pitch gain corresponding to the time series signals and a quantized fixed-codebook gain corresponding to the time series signals;

the index includes the quantized pitch gain or a value corresponding thereto, and the quantized fixed-codebook gain or a value corresponding thereto; and

the condition that indicates high periodicity and/or high stationarity includes a condition in which the ratio of the quantized pitch gain or the value corresponding thereto to the quantized fixed-codebook gain or the value corresponding thereto is larger than a specified value.

8. The encoding method according to one of claims 1 to 4,

wherein the step (A) further comprises a step of obtaining a vector-quantized gain code corresponding to a combination of a quantized pitch gain corresponding to the time series signals or a value corresponding to the quantized pitch gain, and a quantized fixed-codebook gain corresponding to the time series signals or a value corresponding to the quantized fixed-codebook gain;

the index includes the vector-quantized gain code; and

the condition that indicates high periodicity and/or high stationarity includes a condition in which the vector-quantized gain code corresponds to a combination of a quantized pitch gain or a value corresponding thereto, and a quantized fixed-codebook gain or a value corresponding thereto where the ratio of the quantized pitch gain or the value corresponding thereto to the quantized fixed-codebook gain or the value corresponding thereto is larger than a specified value.

9. The encoding method according to one of claims 1 to 4,

wherein the step (A) further comprises a step of obtaining a quantized pitch gain corresponding to the time series signals and a quantized fixed-codebook gain corresponding to the time series signals;

the index includes the quantized pitch gain or a value corresponding thereto and the quantized fixed-codebook gain or a value corresponding thereto; and

the condition that indicates low periodicity and/or low stationarity includes a condition in which the quantized pitch gain or the value corresponding thereto is smaller than a first specified value and the quantized fixed-codebook gain or the value corresponding thereto is smaller than a second specified value.

10. The encoding method according to one of claims 1 to 4,

wherein the step (A) further comprises a step of obtaining a vector-quantized gain code corresponding to a combination of a quantized pitch gain corresponding to the time series signals or a value corresponding to the quantized pitch gain, and a quantized fixed-codebook gain corresponding to the time series signals or a value corresponding to the quantized fixed-codebook gain;

the index includes the vector-quantized gain code; and

the condition that indicates low periodicity and/or low stationarity includes a condition in which the quantized pitch gain corresponding to the vector-quantized gain code or the value corresponding to the quantized pitch gain is smaller than a first specified value and the quantized fixed-codebook gain corresponding to the vector-quantized gain code or the value corresponding to the quantized fixed-codebook gain is smaller than a second specified value.

11. The encoding method according to one of claims 1 to 4,

wherein the step (A) further comprises a step of obtaining a vector-quantized gain code corresponding to a combination of a quantized pitch gain corresponding to the time series signals or a value corresponding to the quantized pitch gain, and a quantized fixed-codebook gain corresponding to the time series signals or a value corresponding to the quantized fixed-codebook gain;

the index includes the vector-quantized gain code; and

the encoding mode is switched according to the vector-quantized gain code while referencing a table in which each vector-quantized gain code is associated with a resolution used to express a pitch period and/or a pitch period encoding mode.

12. The encoding method according to one of claims 1 to 4,

wherein the index includes an index that indicates the ratio of the magnitude of the time series signals to the magnitude of prediction residuals obtained by applying linear prediction analysis to the time series signals;

and

the condition that indicates high periodicity and/or high stationarity includes a condition in which the index that indicates the ratio of the magnitude of the time series signals to the magnitude of the prediction residuals obtained by applying linear prediction analysis to the time series signals is larger than a specified value.

13. The encoding method according to one of claims 1 to 4,

wherein the index includes the magnitude of the difference between a value corresponding to a pitch period in a time interval included in the predetermined time interval and a value corresponding to a pitch period in a past time interval before the time interval included in the predetermined time interval;

and

the condition that indicates high periodicity and/or high stationarity includes a condition in which the magnitude of the difference between the value corresponding to the pitch period in the time interval included in the predetermined time interval and the value corresponding to the pitch period in the past time interval before the time interval included in the predetermined time interval is smaller than a specified value.

29. A program causing a computer to execute processing of the encoding method according to claim 1.

31. A computer readable recording medium having stored therein a program causing a computer to execute processing of the encoding method according to claim 1.

14. A decoding method comprising:

receiving of a code corresponding to a predetermined time interval; and

decoding a code corresponding to pitch periods to obtain the pitch periods corresponding to the predetermined time interval, wherein

a decoding mode for the code corresponding to the pitch periods is switched according to whether an index that indicates a level of periodicity and/or stationarity, the index being included in or obtained from the code corresponding to the predetermined time interval, satisfies a condition that indicates high periodicity and/or high stationarity or a condition that indicates low periodicity and/or low stationarity, and the code corresponding to the predetermined time interval includes the code corresponding to the pitch periods.

15. The decoding method according to claim 14,

wherein the code corresponding to the pitch periods is decoded with a decoding mode that obtains in each first time interval each of the pitch periods expressed at a first resolution, when the index does not satisfy the condition that indicates high periodicity and/or high stationarity;

the code corresponding to the pitch periods is decoded with a decoding mode that obtains in each second time interval each of the pitch periods expressed at a second resolution, when the index satisfies the condition that indicates high periodicity and/or high stationarity; and

the second resolution is higher than the first resolution and/or the second time interval is shorter than the first time interval.

16. The decoding method according to claim 14,

wherein, when the index satisfies the condition that indicates high periodicity and/or high stationarity, in a first predetermined time interval included in the predetermined time interval, a code corresponding to a pitch period in the first predetermined time interval is decoded to obtain the pitch period in the first predetermined time interval where the code corresponding to the predetermined time interval includes the code corresponding to the pitch period;

in a second predetermined time interval included in the predetermined time interval other than the first predetermined time interval, a code corresponding to the difference between a value corresponding to a pitch period in the second predetermined time interval and a value corresponding to a pitch period in a time interval other than the second predetermined time interval is decoded to obtain the difference where the code corresponding to the predetermined time interval includes the code corresponding to the difference; and

the difference and the value corresponding to the pitch period in the time interval other than the second predetermined time interval are used to obtain the pitch period in the second predetermined time interval.

17. The decoding method according to claim 14,

wherein, when the index satisfies the condition that indicates high periodicity and/or high stationarity, in a first predetermined time interval included in the predetermined time interval, a code corresponding to a pitch period in the first predetermined time interval is decoded to obtain the pitch period in the first predetermined time interval where the code corresponding to the predetermined time interval includes the code corresponding to the pitch period;

and

in a plurality of second predetermined time intervals included in the predetermined time interval other than the first predetermined time interval, a code corresponding to information obtained by integrating differences each of which is a difference between a value corresponding to a pitch period in each of the second predetermined time intervals and a value corresponding to a pitch period in each time interval other than the second predetermined time intervals is decoded to obtain the difference where the code corresponding to the predetermined time interval includes the code corresponding to the information obtained by integrating the differences; and

each of the differences and the value corresponding to the pitch period in each time interval other than the second predetermined time intervals are used to obtain the pitch period in each of the second predetermined time intervals.

18. The decoding method according to one of claims 14 to 17,

wherein the index includes a quantized pitch gain or a value corresponding thereto;

and

the condition that indicates high periodicity and/or high stationarity includes a condition in which the quantized pitch gain or the value corresponding thereto is larger than a specified value.

19. The decoding method according to one of claims 14 to 17,

wherein the index includes a vector-quantized gain code corresponding to a combination of a quantized pitch gain or a value corresponding thereto, and a quantized fixed-codebook gain or a value corresponding thereto;

and

the condition that indicates high periodicity and/or high stationarity includes a condition in which the vector-quantized gain code corresponds to a combination of a quantized pitch gain that is larger than a specified value or a value that corresponds to the quantized pitch gain and that is larger than the specified value, and the quantized fixed-codebook gain or the value corresponding thereto.

20. The decoding method according to one of claims 14 to 17,

wherein the index includes a quantized pitch gain or a value corresponding thereto, and a quantized fixed-codebook gain or a value corresponding thereto;

and

the condition that indicates high periodicity and/or high stationarity includes a condition in which the ratio of the quantized pitch gain or the value corresponding thereto to the quantized fixed-codebook gain or the value corresponding thereto is larger than a specified value.

21. The decoding method according to one of claims 14 to 17,

wherein the index includes a vector-quantized gain code corresponding to a combination of a quantized pitch gain or a value corresponding thereto, and a quantized fixed-codebook gain or a value corresponding thereto;

and

the condition that indicates high periodicity and/or high stationarity includes a condition in which the vector-quantized gain code corresponds to a combination of a quantized pitch gain or a value corresponding thereto, and a quantized fixed-codebook gain or a value corresponding thereto where the ratio of the quantized pitch gain or the value corresponding thereto to the quantized fixed-codebook gain or the value corresponding thereto is larger than a specified value.

22. The decoding method according to one of claims 14 to 17,

wherein the index includes a quantized pitch gain or a value corresponding thereto, and a quantized fixed-codebook gain or a value corresponding thereto;

and

the condition that indicates low periodicity and/or low stationarity includes a condition in which the quantized pitch gain or the value corresponding thereto is smaller than a first specified value and the quantized fixed-codebook gain or the value corresponding thereto is smaller than a second specified value.

23. The decoding method according to one of claims 14 to 17,

wherein the index includes a vector-quantized gain code corresponding to a combination of a quantized pitch gain or a value corresponding thereto, and a quantized fixed-codebook gain or a value corresponding thereto;

and

the condition that indicates low periodicity and/or low stationarity includes a condition in which the quantized pitch gain corresponding to the vector-quantized gain code or the value corresponding to the quantized pitch gain is smaller than a first specified value and the quantized fixed-codebook gain corresponding to the vector-quantized gain code or the value corresponding to the quantized fixed-codebook gain is smaller than a second specified value.

24. The decoding method according to one of claims 14 to 17,

wherein the index includes a vector-quantized gain code corresponding to a combination of a quantized pitch gain or a value corresponding thereto, and a quantized fixed-codebook gain or a value corresponding thereto;

and

the decoding mode is switched according to the vector-quantized gain code while referencing a table in which each vector-quantized gain code is associated with a resolution used to express a pitch period and/or a pitch period decoding mode.

25. The decoding method according to one of claims 14 to 17,

wherein the index includes an estimated value of prediction gain calculated by using linear prediction coefficients obtained from the code or coefficients corresponding to the linear prediction coefficients;

and

the condition that indicates high periodicity and/or high stationarity includes a condition in which the estimated value of prediction gain is larger than a specified value.

26. The decoding method according to one of claims 14 to 17,

wherein the index includes the magnitude of the difference between a value corresponding to a pitch period in a time interval included in the predetermined time interval and a value corresponding to a pitch period in a past time interval before the time interval included in the predetermined time interval;

and

the condition that indicates high periodicity and/or high stationarity includes a condition in which the magnitude of the difference between the value corresponding to the pitch period in the time interval included in the predetermined time interval and the value corresponding to the pitch period in the past time interval before the time interval included in the predetermined time interval is smaller than a specified value.

30. A program causing a computer to execute processing of the decoding method according to claim 14.

32. A computer readable recording medium having stored therein a program causing a computer to execute processing of the decoding method according to claim 14.

27. An encoder comprising:

a search unit which obtains pitch periods corresponding to time series signals included in a predetermined time interval; and

a parameter encoding unit which outputs a code corresponding to the pitch periods;

wherein resolutions used to express the pitch periods and/or a pitch period encoding mode are switched according to whether an index that indicates a level of periodicity and/or stationarity of the time series signals satisfies a condition that indicates high periodicity and/or high stationarity or a condition that indicates low periodicity and/or low stationarity.

28. A decoder in which, according to whether an index that indicates a level of periodicity and/or stationarity, the index being included in or obtained from an input code corresponding to a predetermined time interval, satisfies a condition that indicates high periodicity and/or high stationarity or a condition that indicates low periodicity and/or low stationarity, a decoding mode for a code, included in the input code, corresponding to pitch periods is switched to decode the code corresponding to the pitch periods to obtain the pitch periods corresponding to the predetermined time interval.