Audio encoding device and audio encoding method

1. A speech coding apparatus for encoding a stereo signal comprising a first single channel signal and a second single channel signal, the apparatus comprising:

a monaural signal generator, comprising a processor, that generates a monaural signal using the first single channel signal and the second single channel signal;

a selector, comprising a calculator that calculates a first parameter corresponding to the first single channel signal and a second parameter corresponding to the second single channel signal,

the selector compares the first calculated parameter and the second calculated parameter to determine whether a criterion for implementing enhancement layer coding at high efficiency or high sound quality, based upon the comparison of the first calculated parameter and the second calculated parameter, is met, selects the first single channel signal if the criterion is met, and selects the second single channel signal if the criterion is not met;

a coder that encodes the generated monaural signal to obtain core layer encoded data, and encodes the selected single channel signal to obtain enhancement layer encoded data corresponding to the core layer encoded data; and

an outputter that outputs encoded data so that the encoded data is transmitted to speech decoding apparatus,

wherein:

the enhancement layer encoded data do not contain encoded data of an unselected single channel signal; and

the encoded data includes selection information that represents which of the single channel signals the selector selected, the core layer encoded data and the enhancement layer encoded data.

2. The speech coding apparatus of claim 1 , wherein:

the selector selects one of the first single channel signal and the second single channel signal every frame; and

the coder encodes the monaural signal and the single channel signal selected every frame, every frame.

3. The speech coding apparatus of claim 1 , wherein the calculator calculates a first coding distortion occurring when the first single channel signal is selected and a second coding distortion occurring when the second single channel signal is selected,

wherein the selector selects the first single channel signal when the calculated first coding distortion is smaller than the calculated second coding distortion, and selects the second single channel signal when the calculated second coding distortion is smaller than the calculated first coding distortion.

4. The speech coding apparatus of claim 3 , wherein the coder encodes the first single channel signal and the second single channel signal to obtain first coded data and second coded data, respectively, and outputs one of the first coded data and the second coded data corresponding to the selected single channel signal as the enhancement layer encoded data, and comprises:

an estimation signal generator that generates a second channel estimation signal corresponding to the second channel using a monaural decoded signal obtained when the coder encodes the monaural signal and a first channel decoded signal obtained when the coder encodes the first single channel signal, and generates a first channel estimation signal corresponding to the first single channel signal using the monaural decoded signal and a second channel decoded signal obtained when the coder encodes the second single channel signal; and

a distortion calculator that calculates the first coding distortion based on error of the first channel decoded signal with respect to the first single channel signal and error of the second channel estimation signal with respect to the second single channel signal, and calculates second coding distortion based on error of the first channel estimation signal with respect to the first single channel signal and error of the second channel decoding signal with respect to the second single channel signal.

5. The speech coding apparatus of claim 1 , wherein the calculator that calculates a first intra-channel correlation corresponding to the first single channel signal and a second intra-channel correlation corresponding to the second single channel signal, selects the first single channel signal when the calculated first intra-channel correlation is greater than the calculated second intra-channel correlation, and selects the second single channel signal when the calculated second intra-channel correlation is greater than the calculated first intra-channel correlation.

6. The speech coding apparatus of claim 1 , wherein the coder carries out code excited linear prediction coding of the first single channel signal using a first adaptive codebook when the first single channel signal is selected by the selector, obtains the enhancement layer encoded data using code excited linear prediction coding results and updates the first adaptive codebook using the code excited linear prediction coding results.

7. The speech coding apparatus of claim 6 , wherein the coder generates a second channel estimation signal corresponding to the second single channel signal using the enhancement layer encoded data and a monaural decoded signal obtained when the monaural signal is encoded, and updates the second adaptive codebook used in code excited linear prediction coding of the second single channel signal using an linear prediction coding prediction residual signal for the second channel estimation signal.

8. The speech coding apparatus of claim 7 , wherein:

the selector correlates the first single channel signal to a frame having a subframe and selects the first single channel signal; and

the coder obtains the enhancement layer encoded data for the frame while carrying out excitation search every subframe for the monaural signal and the first single channel signal correlated with the frame and selected.

9. The speech coding apparatus of claim 8 , wherein the coder updates the first adaptive codebook per subframe and updates the second adaptive codebook per frame.

10. A mobile station apparatus comprising the speech coding apparatus of claim 1 .

11. A base station apparatus comprising the speech coding apparatus of claim 1 .

12. A speech coding method for encoding a stereo signal comprising a first single channel signal and a second single channel signal, the method comprising:

generating a monaural signal using the first single channel signal and the second single channel signal;

calculating a first parameter corresponding to the first single channel signal and a second parameter corresponding to the second single channel signal;

comparing the first calculated parameter and the second calculated parameter to determine whether a criterion for implementing enhancement layer coding at high efficiency or high sound quality, based upon the comparison of the first calculated parameter and the second calculated parameter, is met;

selecting the first single channel signal if the criterion is met;

selecting the second single channel signal if the criterion is not met;

encoding a generated monaural signal to obtain core layer encoded data and encoding a selected single channel signal to obtain enhancement layer encoded data corresponding to the core layer encoded data; and

outputting encoded data so that the encoded data is transmitted to a speech decoding apparatus,

wherein:

the enhancement layer encoded data do not contain encoded data of an unselected single channel signal; and

the encoded data includes selection information that represents which of the single channel signals was selected, the core layer encoded data and the enhancement layer encoded data.