Apparatus and method for encoding and decoding multi-channel signal

1. An encoding apparatus comprising:

a parameter extractor to extract a plurality of parameters that indicate a characteristic relationship between a plurality of channels constituting a multi-channel signal;

a parameter modifier to modify a phase parameter associated with phase information between the plurality of channels, among the plurality of parameters;

a parameter encoder to encode the plurality of parameters that includes the modified phase parameter;

a mono signal encoder to encode a mono signal that is a down-mixed signal of the multi-channel signal; and

a bitstream generator to generate an encoded bitstream with respect to the multi-channel signal using the encoded parameters and the encoded mono signal using at least one processor.

2. The encoding apparatus of claim 1 , wherein the phase parameter includes an inter-channel phase difference parameter (IPD) that indicates a phase difference between the plurality of channels.

3. The encoding apparatus of claim 2 , wherein:

the plurality of parameters includes a channel level difference parameter (CLD) that indicates a level difference between the plurality of channels, and

when the CLD is zero and the IPD is 180 degrees, the parameter modifier modifies the IPD to zero degrees.

4. An encoding apparatus comprising:

a parameter extractor to extract a plurality of parameters that indicate a characteristic relationship between a plurality of channels constituting a multi-channel signal; and

a parameter encoder to determine whether to encode a phase parameter associated with phase information between the plurality of channels, among the plurality of parameters, and to encode the plurality of parameters that includes the phase parameter, upon determining the phase parameter is to be encoded using at least one processor.

5. The encoding apparatus of claim 4 , wherein:

the plurality of parameters includes an inter-channel coherence parameter or an inter-channel correlation parameter (ICC) that indicates a coherence or a correlation between the plurality of channels,

the phase parameter includes an inter-channel phase difference parameter (IPD), and

when a difference between an ICC extracted using the IPD and an ICC extracted without using the IPD is greater than a predetermined value, the parameter encoder determines to encode the IPD.

6. The encoding apparatus of claim 4 , wherein:

the multi-channel signal includes a plurality of frames, and

the parameter encoder determines whether to encode the phase parameter, upon a continuity of phase information between the plurality of frames.

7. The encoding apparatus of claim 6 , wherein the parameter encoder determines the continuity of the phase information based on a phase information value of a current frame, a phase information value of a previous frame being one frame prior to the current frame, and a phase information value of a previous frame being two frames prior to the current frame.

8. The encoding apparatus of claim 6 , wherein:

the parameter encoder calculates a first phase difference value that is a difference between a two-fold value of the phase information value of the previous frame being one frame prior to the current frame and the phase information value of the previous frame being two frames prior to the current frame, and calculates a second phase difference value that is a difference between the phase information value of the current frame and the first phase difference value, and

when the second phase difference value is greater than a predetermined value, the parameter encoder determines the phase information is discontinuous and determines to encode the phase parameter.

9. The encoding apparatus of claim 4 , wherein:

the plurality of parameters includes an inter-channel correlation parameter (ICC),

the phase parameter includes an inter-channel phase difference parameter (IPD),

the parameter extractor extracts the ICC parameter using the IPD, and

the parameter encoder encodes the plurality of parameters that includes the ICC, extracted using the IPD, and the IPD.

10. The encoding apparatus of claim 9 , wherein the IPD is quantized.

11. An encoding apparatus comprising:

a parameter extractor to extract a plurality of parameters that indicate a characteristic relationship between a plurality of channels constituting a multi-channel signal;

a parameter encoder to quantize the plurality of parameters and to encode the quantized parameters;

a mono signal encoder to encode a mono signal that is a down-mixed signal of the multi-channel signal; and

a bitstream generator to generate an encoded bitstream with respect to the multi-channel signal using the encoded parameters and the encoded mono signal using at least one processor,

wherein the extracted parameters include a phase parameter associated with phase information between the plurality of channels included in the multi-channel signal, and

wherein the parameter encoder determines a quantization type of the phase parameter based on a continuity of phase information between a plurality of frames included in the multi-channel signal.

12. The encoding apparatus of claim 11 , wherein:

the parameter encoder quantizes the phase parameter according to a first quantization type, upon determining the phase information is discontinuous, and

the parameter encoder quantizes the phase parameter according to a second quantization type, upon determining the phase information is continuous, and

a quantization error of the first quantization type is different from a quantization error of the second quantization type.

13. The encoding apparatus of claim 12 , wherein:

the multi-channel signal includes the plurality of frames,

the parameter encoder calculates a first phase difference value that is a difference between a two-fold value of a phase information value of a previous frame being one frame prior to a current frame and a phase information value of a previous frame being two frames prior to the current frame, and calculates a second phase difference value that is a difference between a phase information value of the current frame and the first phase difference value, and

when the second phase difference value is less than or equal to a predetermined value, the parameter encoder determines the phase information is continuous, and when the second phase difference value is greater than the value, the parameter encoder determines the phase information is discontinuous.

14. An apparatus for generating a multi-channel signal from a down-mixed mono signal, the apparatus comprising:

a parameter decoder to decode a plurality of parameters that indicate characteristic relations between channels;

a parameter estimator to estimate an overall phase difference (OPD) parameter representing a phase difference between one of a left signal and a right signal and the down-mixed mono signal, based on values of the decoded parameters; and

an up-mixer, implemented by at least one processor, to up-mix the down-mixed mono signal using the decoded parameters and the estimated OPD parameter

15. The apparatus of claim 14 , wherein:

the plurality of parameters includes a channel level difference (CLD) parameter and an inter-channel phase difference (IPD) parameter, and

the OPD parameter is estimated based on the CLD parameter and the IPD parameter.

16. The apparatus of claim 15 , wherein, when the IPD parameter is 180 degrees, the OPD parameter is set to zero.

17. The apparatus of claim 15 , wherein:

when the IPD parameter is not 180 degrees, the OPD parameter is estimated using the CLD parameter and the IPD parameter, and

the estimated OPD parameter corresponds to either a value between the estimated OPD parameter and zero or a value between the estimated OPD parameter and -180 degrees.

18. The apparatus of claim 14 , wherein the estimated OPD parameter is filtered to decrease a change amount of the estimated OPD parameter.

19. The decoding apparatus of claim 18 , wherein the estimated OPD is filtered using an infinite impulse response filter.

20. A decoding apparatus comprising:

a mono signal decoder to restore, from an encoded bitstream of a multi-channel signal, a mono signal that is a down-mixed signal of the multi-channel signal;

a parameter decoder to restore, from the bitstream, a quantized first phase parameter with respect to phase information between a plurality of channels constituting the multi-channel signal, and quantization type information of the quantized first phase parameter, and to perform inverse quantization for the quantized first phase parameter based on the quantization type information to calculate a second phase parameter using at least one processor; and

an up-mixer to up-mix the mono signal using the second phase parameter.

21. The decoding apparatus of claim 20 , wherein:

when the quantization type information corresponds to a first quantization type, the parameter decoder restores the second phase parameter based on the first quantization type,

when the quantization type information corresponds to a second quantization type, the parameter decoder restores the second phase parameter based on the second quantization type, and

a quantization error of the first quantization type is different from a quantization error of the second quantization type.