Method and apparatus for encoding and decoding stereo signal and multi-channel signal

1. A method of decoding a stereo signal, comprising:

decoding a parameter that represents a ratio of the amplitude of at least one of signals contained in the stereo signal to the amplitude of a mono signal;

decoding a parameter that represents the difference between the phases of at least one of the signals contained in the stereo signal and the mono signal; and

upmixing the mono signal to the stereo signal by using the decoded parameters.

2. The method of claim 1 , further comprising decoding a parameter for adjusting the phase difference by using a decorrelated signal.

3. The method of claim 1 , wherein the upmixing of the mono signal to the stereo signal comprises:

determining the amplitude of the stereo signal by using the decoded parameter that represents the ratio of amplitude;

determining the phase of the stereo signal by using the decoded parameter that represents the phase difference; and

generating the stereo signal according to the determined amplitude and phase.

4. The method of claim 2 , wherein the upmixing of the mono signal to the stereo signal comprises:

determining the amplitude of the stereo signal by using the decoded parameter that represents the ratio of amplitude;

determining the phase of the stereo signal by using the decoded parameter that represents the phase difference;

adjusting the determined phase of the stereo signal by using the parameter for adjusting the phase difference; and

generating the stereo signal according to the determined amplitude and phase.

5. The method of claim 1 , wherein at least one of the parameters is generated for each frame, in band units.

6. The method of claim 1 , further comprising transforming the stereo signal into a domain for expressing both the amplitude and phase of the stereo signal.

7. The method of claim 1 , wherein the mono signal is generated on a half sum vector of the stereo signal.

8. The method of claim 1 , wherein the mono signal is downmixed to an amplitude equal to the average amplitude of the signals contained in the stereo signal.

9. The method of claim 1 , wherein, if the phase of the stereo signal is adjusted and encoded since the difference between the phases of a left-channel signal and a right-channel signal contained in the stereo signal falls within a predetermined, further comprising adjusting the phase of the upmixed stereo signal.

10. The method of claim 9 , wherein the predetermined range is determined based on 180 degrees.

11. The method of claim 9 , further comprising encoding information related to the adjusted phase.

12. The method of claim 3 , wherein the determining of the phase of the stereo signal is based on an assumption that the difference between the phases of the mono signal and a left-channel signal is equal to the difference between the phases of the mono signal and a right-channel signal.

13. The method of claim 1 , wherein the relation between the amplitudes of a left-channel signal and a right-channel signal that are contained in the stereo signal is predetermined.

14. A non-transitory computer readable medium having recorded thereon a computer program for executing a method of decoding a stereo signal, the method comprising:

decoding a parameter that represents a ratio of the amplitude of at least one of signals contained in the stereo signal to the amplitude of a mono signal;

decoding a parameter that represents the difference between the phases of at least one of the signals contained in the stereo signal and the mono signal; and

upmixing the mono signal to the stereo signal by using the decoded parameters.

15. An apparatus for decoding a stereo signal, comprising:

a size parameter decoding unit decoding a parameter that represents a ratio of the amplitude of at least one of signals contained in the stereo signal to the amplitude of a mono signal;

a phase parameter decoding unit decoding a parameter that represents the difference between the phases of at least one of the signals contained in the stereo signal and the mono signal; and

an upmixing unit upmixing the mono signal to the stereo signal by using the decoded parameters.

16. The apparatus of claim 15 , further comprising an enhancement parameter decoding unit decoding a parameter for adjusting the phase difference by using a decorrelated signal.

17. The apparatus of claim 16 , wherein the up-mixing unit comprises:

a amplitude determination unit determining the amplitude of the stereo signal by using the decoded parameter that represents the ratio of amplitude;

a phase determination unit determining the phase of the stereo signal by using the decoded parameter that represents the phase difference;

a phase adjustment unit adjusting the determined phase of the stereo signal by using the parameter for adjusting the phase difference; and

a signal generation unit generating the stereo signal according to the determined amplitude and phase.

18. The apparatus of claim 15 , further comprising:

adjusting the phase of the upmixed stereo signal if the phase of the stereo signal is adjusted and encoded since the difference between the phases of a left-channel signal and a right-channel signal contained in the stereo signal falls within a predetermined.

19. The apparatus of claim 15 , wherein the phase determination unit determines the phase of the stereo signal, based on an assumption that the difference between the phases of the mono signal and a left-channel signal is equal to the difference between the phases of the mono signal and a right-channel signal.

20. An apparatus for decoding a multi-channel signal, comprising:

a size parameter decoding unit decoding a parameter that represents a ratio of the amplitude of at least one of the signals contained in the multi-channel signal to the amplitude of at least one of downmixed signals, where the multi-channel signal comprises at least two signals;

a phase parameter decoding unit decoding a parameter that represents the difference between phases of least one of the signals of the multi-channel signal and at least one of the downmixed signals; and

an upmixing unit upmixing the downmixed signals to the multi-channel signal by using the decoded parameters.