Frame loss recovering method, and audio decoding method and device using same

1. A method of recovering a frame loss, the method comprising:

grouping transform coefficients of at least one frame into a predetermined number of bands among previous frames of a current frame;

deriving an attenuation constant according to a tonality of the bands; and

recovering transform coefficients of the current frame by applying the attenuation constant to the previous frame of the current frame,

wherein, in a band having a strong tonality, the attenuation constant is derived on the basis of a correlation between transform coefficients of previous normal frames.

2. The method of claim 1 , wherein the attenuation constant is derived on the basis of transform coefficients of previous N normal frames (where N is an integer) of the current frame.

3. The method of claim 2 , wherein the N is the number of buffers for storing information of the previous frame.

4. The method of claim 1 , wherein a per-band correlation is used as a per-band attenuation constant, and a band having a high positional correlation of an inter-frame sinusoidal pulse has a high correlation.

5. The method of claim 4 , wherein the per-band correlation is calculated based on a following equation,

correlation

=

W

m

×

∑

band

-

end

band

-

start

⁢

(

N

i

,

n

-

1

×

N

i

,

n

-

2

)

where, W m denotes a weight for the current band, n represents an index number of the current frame, N i,n−1 denotes an i-th sinusoidal pulse of an (n−1)-th frame, and N i,n−2 denotes an i-th sinusoidal pulse of an (n−2)-th frame.

6. The method of claim 1 , wherein the transform coefficient of the current frame is recovered to a value obtained by multiplying an attenuation constant derived for each band by a per-band transform coefficient of the previous frame.

7. The method of claim 6 , wherein if the previous frame of the current frame is a recovered frame, the transform coefficient of the current frame is recovered by additionally applying the attenuation constant of the current frame to the attenuation constant of the previous frame.

8. An audio decoding method comprising:

determining whether there is a loss in a current frame;

if the current frame has lost, recovering a transform coefficient of the current frame on the basis of transform coefficients of previous frames of the current frame; and

inverse-transforming the recovered transform coefficient,

wherein the recovering of the transform coefficient comprises:

grouping transform coefficients of at least one frame into a predetermined number of bands among previous frames of the current frame;

deriving an attenuation constant according to a tonality of the bands; and

recovering transform coefficients of the current frame by applying the attenuation constant to the previous frame of the current frame, and

wherein, in a band having a strong tonality, the attenuation constant is derived on the basis of a correlation between transform coefficients of previous normal frames.

9. The audio decoding method of claim 8 , wherein the attenuation constant is derived on the basis of transform coefficients of a specific number of previous normal frames of the current frame.

10. The audio decoding method of claim 8 , wherein the transform coefficient of the current frame is recovered to a value obtained by multiplying an attenuation constant derived for each band by a per-band transform coefficient of the previous frame.

11. The audio decoding method of claim 10 , wherein if the previous frame of the current frame is a recovered frame, the transform coefficient of the current frame is recovered by additionally applying the attenuation constant of the current frame to the attenuation constant of the previous frame.