Method and apparatus for encoding and decoding audio signal to reduce quantization noise

1. A method of encoding an audio signal in of an encoding device, the method comprising:

identifying an audio signal of a time domain;

extracting a first residual signal of a frequency domain represented by a complex number from the audio signal of a time domain using linear predictive coding of a time domain;

converting the first residual signal into a time domain;

generating a second residual signal of a time domain from the converted first residual signal using linear predictive coding of a frequency domain;

quantizing a plurality of the second residual signals;

encoding a linear predictive coefficient of a time domain, linear predictive coefficient of a frequency domain, and the second residual signal into a bitstream; and

outputting the bitstream to a decoding device,

wherein the quantizing of the plurality of second residual signals comprises:

grouping the plurality of second residual signals for each sub-band;

determining a scale factor for quantization for each group of the plurality of second residual signals; and

quantizing the plurality of second residual signals using the scale factor.

2. The method of claim 1 , wherein the identifying an audio signal of a time domain comprises:

identifying an audio signal of a time domain in units of a block,

further comprising:

generating a combined block by combining i) a current original block of the audio signal and ii) a previous original block chronologically adjacent to the current original block.

3. The method of claim 1 , further comprising:

quantizing a linear predictive coefficient of a time domain extracted from the combined block of the audio signal; and

generating a frequency envelope by inversely quantizing the linear predictive coefficient of the time domain,

wherein the extracting of the first residual signal generates a first residual signal from the combined block converted into a frequency domain based on the frequency envelope, and

the encoding into the bitstream additionally encodes the quantized linear predictive coefficient of the time domain into a bitstream.

4. The method of claim 1 , further comprising:

overlapping first residual signals chronologically adjacent to each other among the first residual signals converted into a time domain;

quantizing a linear predictive coefficient of a frequency domain extracted from the overlapped first residual signal using linear predictive coding of a frequency domain;

generating a time envelope by inversely quantizing the linear predictive coefficient of the frequency domain; and

extracting a second residual signal of a time domain from the overlapped first residual signal based on the time envelope,

wherein the encoding into the bitstream additionally encodes the quantized linear predictive coefficient of the frequency domain into a bitstream.

5. The method of claim 4 , wherein the quantizing of the linear predictive coefficient of the frequency domain comprises:

performing Hilbert-transformation on the overlapped first residual signal;

converting the Hilbert-transformed first residual signal and the overlapped residual signal into a frequency domain;

extracting a linear predictive coefficient of a frequency domain corresponding to the Hilbert-transformed first residual signal and the overlapped first residual signal using linear predictive coding; and

quantizing the linear predictive coefficient of the frequency domain.

6. The method of claim 4 , wherein the extracting of the second residual signal comprises:

generating a current envelope interpolated from a time envelope using symmetric windowing; and

extracting a second residual signal of a time domain from the overlapped first residual signal based on the current envelope.

7. The method of claim 2 , wherein the first residual signal corresponds to two original blocks chronologically adjacent to each other, and

the overlapping of the first residual signal overlaps two first residual signals corresponding to an original block belonging to a predetermined time among first residual signals adjacent chronologically.

8. The method of claim 3 , wherein the generating of the frequency envelope comprises:

converting inversely quantized linear predictive coefficients of the time domain into a frequency domain;

grouping the converted linear predictive coefficients of the time domain for each sub-band; and

generating a frequency envelope corresponding to the combined block by calculating energy of the grouped linear predictive coefficients of the time domain.

9. The method of claim 1 , wherein the determining of the scale factor determines the scale factor based on an intermediate value of a frequency envelope corresponding to the second residual signal or determines the scale factor based on a number of bits available for quantization of the second residual signal.

10. A method of decoding an audio signal of a decoding device, the method comprising:

receiving a bitstream from an encoding device;

extracting a linear predictive coefficient of a time domain, a linear predictive coefficient of a frequency domain, and a second residual signal of a frequency domain from the bitstream;

converting the second residual signal into a time domain;

converting the second residual signal into a time domain by inversely quantizing a plurality of the second residual signals;

generating a first residual signal of a frequency domain from the converted second residual signal using the linear predictive coefficient of the time domain;

converting the first residual signal into a time domain;

restoring an audio signal of a frequency domain from the converted first residual signal using the linear predictive coefficient of the frequency domain; and

converting the audio signal in the frequency domain into a time domain,

wherein the inversely quantizing of the plurality of second residual signals is performed by inversely performing quantizing of the plurality of second residual signals, and

wherein the quantizing of the plurality of second residual signals comprises:

grouping the plurality of second residual signals for each sub-band;

determining a scale factor for quantization for each group of the plurality of second residual signals; and

quantizing the plurality of second residual signals using the scale factor.

11. The method of claim 10 , wherein the restored audio signal includes a combined block,

further comprising:

generating a restored block by overlapping original blocks corresponding to a same point in time among original blocks included in the restored combined blocks adjacent chronologically.

12. The method of claim 10 , wherein the generating of the first residual signal comprises:

generating a current envelope interpolated from a time envelope using symmetric windowing;

and

generating the first residual signal from the converted second residual signal using the current envelope.

13. An encoding device for performing a method of encoding an audio signal, the encoding device comprising:

a processor,

wherein the processor is configured to identify an audio signal of a time domain, extract a first residual signal of a frequency domain represented by a complex number from the audio signal of a time domain using linear predictive coding of a time domain, convert the first residual signal into a time domain, generate a second residual signal of a time domain from the converted first residual signal using linear predictive coding of a frequency domain, quantize a plurality of the second residual signals, and encode a linear predictive coefficient of a time domain, linear predictive coefficient of a frequency domain, and the second residual signal into a bitstream, and output the bitstream to a decoding device,

wherein the quantizing of the plurality of second residual signals comprises:

grouping the plurality of second residual signals for each sub-band;

determining a scale factor for quantization for each group of the plurality of second residual signals; and

quantizing the plurality of second residual signals using the scale factor.

14. The encoding device of claim 13 , wherein the processor is configured to identify an audio signal of a time domain in units of a block, generate a combined block by combining i) a current original block of the audio signal and ii) a previous original block chronologically adjacent to the current original block.

15. The encoding device of claim 13 , wherein the processor is configured to quantize a linear predictive coefficient of a time domain extracted from the combined block of the audio signal, generate a frequency envelope by inversely quantizing the linear predictive coefficient of the time domain, generate a first residual signal from the combined block converted into a frequency domain based on the frequency envelope, and additionally encode the quantized linear predictive coefficient of the time domain into a bitstream.