1. A coding apparatus comprising: a down-sampler for down-sampling an input signal; a core coder for performing core coding on the down-sampled input signal; a frequency transformer for performing frequency transformation on the input signal; and an extension coder for performing bandwidth extension coding by using a base signal of the input signal in a frequency domain.

2. The coding apparatus of claim 1, wherein the extension coder comprises: a base signal generator for generating the base signal of the input signal in the frequency domain from a frequency spectrum of the input signal in the frequency domain; a factor estimator for estimating an energy control factor by using the base signal; an energy extractor for extracting energy from the input signai in the frequency domain; an energy controller for controlling the extracted energy by using the energy control factor; and an energy quantizer for quantizing the controlled energy.

3. The coding apparatus of claim 2, wherein the base signal generator comprises: an artificial signal generator for generating an artificial signal corresponding to a high-frequency band by copying and folding a low-frequency band of the input signal in the frequency domain; an envelope estimator for estimating an envelope of the base signal by using a window; and an envelope application unit for applying the estimated envelope to the artificial signal.

4. The coding apparatus of claim 3, wherein a peak of the window corresponds to a frequency index for estimating the envelope of the base signal, and the envelope estimator estimates the envelope of the base signal by selecting a window according to comparison of a tonality or correlation.

5. The coding apparatus of claim 3, wherein the envelope estimator estimates an average of frequency magnitudes of each of whitening bands as an envelope of a frequency belonging to the whitening band.

6. The coding apparatus of claim 5, wherein the envelope estimator estimates the envelope of the base signal by controlling a number of frequency spectrums belonging to the whitening band according to a core coding mode.

7. The coding apparatus of claim 2, wherein the factor estimator comprises: a first tonality calculator for calculating a tonality of a high-frequency band of the input signal in the frequency domain; a second tonality calculator for calculating a tonality of the base signal; and a factor calculator for calculating the energy control factor by using the tonality of the high-frequency band of the input signal and the tonality of the base signal.

8. The coding apparatus of claim 2, wherein, if the energy control factor is less than a predetermined threshold energy control factor, the energy controller controls energy of the input signal.

9. The coding apparatus of claim 2, wherein the energy quantizer selects and quantizes a sub vector, and quantizes remaining sub vectors by using an interpolation error

10. The coding apparatus of claim 9, wherein the energy quantizer selects a sub vector at a same time interval and performs quantization

11. The coding apparatus of claim 9, wherein the energy quantizer selects candidates of the sub vector and performs multi-stage vector quantization using at least two stages

12. The coding apparatus of claim 9, wherein the energy quantizer generates an index set to satisfy mean square errors (MSEs) or weighted mean square errors', '(WMSEs) for each of candidates of the sub vector in each of stages, and selects a candidate of sub vector having a least sum of MSEs or WMSECSs in all the stages from among the candidates

13. The coding apparatus of claim 9, wherein the energy quantizer generates an index set to minimize mean square errors (MSEs) or weighted mean square errors (WMSEs) for each of candidates of the sub vector in each of stages, reconstructs energy vector through inverse quantization, and selects a candidate of sub vector to minimize MSE or WMSEC between the reconstructed energy vector and the original energy vector from among the candidates

14. A coding apparatus comprising: a down-sampler for down-sampling an input signal; a core coder for performing core coding on the down-sampled input signal; a frequency transformer for performing frequency transformation on the input signal; and an extension coder for performing bandwidth extension coding by using characteristics of the input signal and a base signal of the input signal in a frequency domain

15. The coding apparatus of claim 14, wherein the extension coder comprises: a base signal generator for generating the base signal of the input signal in the frequency domain by using a frequency spectrum of the input signal in the frequency domain; a factor estimator for estimating an energy control factor by using the characteristics of the input signal and the base signal; an energy extractor for extracting energy from the input signal in the frequency domain; an energy controller for controlling the exiracted energy by using the energy control factor; and an energy quantizer for quantizing the controlled energy

16. The coding apparatus of claim 15, wherein the extension coder further comprises a signal classification unit for classifying the input signal in the frequency domain according to characteristics of this input signal by using the frequency spectrum of the input signal in the frequency domain, and wherein the factor estimator estimates the energy control factor by using the characteristics of the input signal which are determined by the signal classification unit,17. The coding apparatus of claim 15, wherein the factor estimator estimates the energy control factor by using characteristics of the input signal, which are determined by the core coder

18. The coding apparatus of claim 15, wherein the base signal generator comprises: an artificial signal generator for generating an artificial signal corresponding to a high-frequency band by copying and folding a low-frequency band of the input signal in the frequency domain; an envelope estimator for estimating an envelope of the base signal by using a window; and an envelope application unit for applying the estimated envelope to the artificial signal

19. The coding apparatus of claim 18, wherein a peak of the window corresponds to a frequency index for estimating the envelope of the base signal, and the envelope estimator estimates the envelope of the base signal by selecting a window according to comparison of a tonality or correlation.

20. The coding apparatus of claim 18, wherein the envelope estimator estimates an average of frequency magnitudes of each of whitening bands as an envelope of a frequency belonging to the whitening band.

21. The coding apparatus of claim 20, wherein the envelope estimator estimates the envelope of the base signal by controlling a number of frequency spectrums belonging to the whitening band according to a core coding mode.

22. The coding apparatus of claim 14, wherein the factor estimator comprises:', 'a first tonality calculator for calculating a tonality of a high-frequency band of the input signal in the frequency domain; a second tonality calculator for calculating a tonality of the base signal; and : a factor calculator for calculating the energy control factor by using the tonality of the high-frequency band of the input signal in the frequency domain and the tonality of the base signal.

23. The coding apparatus of claim 15, wherein, if the energy control factor is less than a predetermined threshold energy control factor, the energy controller controls energy of the input signal.

24. The coding apparatus of claim 15, wherein the energy quantizer selects and quantizes a sub vector, and quantizes remaining sub vectors by using an interpolation error.

25. The coding apparatus of claim 24, wherein the energy quantizer selects a sub vector at a same time interval and performs quantization.

26. The coding apparatus of claim 24, wherein the energy quantizer selects candidates of the sub vector and performs multi-stage vector quantization using at least two stages.

27. A coding apparatus comprising: an energy extractor for extracting energy from an input signal in a frequency domain, based on a coding mode; an energy controller for controlling energy, based on the coding mode; and an energy quantizer for quantizing the energy, based on the coding mode.

28. A coding apparatus comprising: a coding mode selector for selecting a coding mode of bandwidth extension coding, based on an input signal in a frequency domain and an input signal in a time domain; and an extension coder for performing bandwidth extension coding by using the input signal in the frequency domain and the coding mode.

29. The coding apparatus of claim 28, wherein the coding mode selector classifies the input signal in the frequency domain by using the input signal in the frequency domain and the input signal in the time domain, determines a coding mode of bandwidth extension coding according to classified information, and determines a number of frequency bands according to the coding mode.

30. The coding apparatus of claim 28, wherein the extension coder comprises: an energy extractor for extracting energy from the input signal in the frequency domain, based on the coding mode; an energy controller for controlling the extracted energy by using the energy control factor, based on the coding mode; and an energy quantizer for quantizing the controlled energy, based on the coding mode.

31. The coding apparatus of claim 30, wherein the energy extractor extracts energy corresponding to a frequency band, based on the coding mode.

32. The coding apparatus of claim 30, wherein the energy controller controls energy by using an energy control factor estimated according to a base signal of the input signal in the frequency domain.

33. The coding apparatus of claim 30, wherein the energy quantizer performs quantization to be optimized for the input signal in the frequency domain, according to the coding mode.

34. The coding apparatus of claim 30, wherein the energy quantizer performs quantization to be optimized for the input signal in the frequency domain, according to the coding mode.

35. The coding apparatus of claim 34, wherein the frequency weighting method is a method for quantizing energy by assigning a weight to a low-frequency band of high perceptual importance.

36. The coding apparatus of claim 33, wherein, if the coding mode is a normal mode or a harmonic mode, the energy quantizer quantizes energy of a frequency band by using an unequal bit allocation method.

37. The coding apparatus of claim 36, wherein the unequal bit allocation method is a method for quantizing energy by assigning a larger number of bits to a low-frequency band of high perceptual importance than to a high-frequency band.

38. The coding apparatus of claim 30, wherein the energy quantizer predicts a representative value of a quantization target vector including at least two elements, and performs vector quantization on an error signal between the predicted representative value and the each of elements of the quantization target vector.

39. A decoding apparatus comprising: a core decoder for performing core decoding on a core coded input signal included in a bitstream; an up-sampler for up-sampling the core decoded input signal; a frequency transformer for performing frequency transformation on the up-sampled input signal; and an extension decoder for performing bandwidth extension decoding by using energy of the input signal included in the bitstream and an input signal in a frequency domain.

40. The decoding apparatus of claim 39, wherein the extension decoder comprises: an inverse quantizer for inversely quantizing the energy of the input signal; a base signal generator for generating a base signal by using the input signal in the frequency domain; a gain calculator for calculating a gain to be applied to the base signal by using the inversely quantized energy and energy of the base signal; and a gain application unit for applying the gain to each of frequency bands.

41. The decoding apparatus of claim 40, wherein the inverse quantizer selects and inversely quantizes a sub vector, interpolates the inversely quantized sub vector, and inversely quantizes energy by adding an interpolation error to the interpolated sub vector.

42. The decoding apparatus of claim 40, wherein the base signal generator comprises: an artificial signal generator for generating an artificial signal corresponding to a high-frequency band by copying and folding a low-frequency band of the input signal in the frequency domain; an envelope estimator for estimating an envelope of the base signal by using a window included in the bitstream; and an envelope application unit for applying the estimated envelope to the artificial signal.

43. The decoding apparatus of claim 40, wherein the gain calculator and the gain application unit generate energy of each of the sub bands through interpolation by setting sub band for applying energy smoothing, the gain is calcuiated for the each sub band.

44. A coding apparatus comprising: a signal classification unit for determining a coding mode of an input signal, based on characteristics of the input signal; a code excited linear prediction (CELP) coder for performing CELP coding on a low-frequency signal of the input signal when a coding mode of the input signal is determined as a CELP coding mode; a time-domain (TD) extension coder for performing extension coding on a high-frequency signal of the input signal when CELP coding is performed on the low-frequency signal of the input signal; a frequency transformer for performing frequency transformation on the input signal when the coding mode of the input signal is determined as a frequency-domain (FD) mode; and an FD coder for performing FD coding on the transformed input signal.

45. The coding apparatus of claim 44, wherein the FD coder comprises:', 'a normalization coder for extracting energy from the transformed input signal for each frequency band and quantizing the extracted energy; a factorial pulse coder for performing factorial pulse coding (FPC) on a value obtained by scaling the transformed input signal by using a quantized normalization value; and an additional noise information generator for generating additional noise information according to performing of the FPC, wherein the transformed input signal input to the FD coder is a transient frame.

46. The coding apparatus of claim 44, wherein the FD coder comprises: a normalization coder for extracting energy from the transformed input signal for each frequency band and quantizing the extracted energy; a factorial pulse coder for performing factorial pulse coding (FPC) on a value obtained by scaling the transformed input signal by using a quantized normaiization value; an additional noise information generator for generating additional noise information according to performing of the FPC; and an FD extension coder for performing extension coding on a high-frequency signal of the transformed input signal, wherein the transformed input signal input to the FD coder is a stationary frame.

47. The coding apparatus of claim 46, wherein the FD extension coder performs energy quantization by using a same codebook at different bitrates.

48. The coding apparatus of claim 44, wherein a bitstream according to a result of performing the FD coding on the transformed input signal includes previous frame mode information.

49. A coding apparatus comprising: a signal classification unit for determining a coding mode of an input signal, based on characteristics of the input signal; a linear prediction coefficient (LPC) coder for extracting an LPC from a low-frequency signal of the input signal, and quantizing the LPC; a code excited linear prediction (CELP) coder for performing CELP coding on an', 'LPC excitation signal of a low-frequency signal of the input signal extracted using the LPC when a coding mode of the input signal is determined as a CELP coding mode; a time-domain (TD) extension coder for performing extension coding on a high-frequency signal of the input signal when CELP coding is performed on the LPC excitation signal; an audio coder for performing audio coding on the LPC excitation signal when a coding mode of the input signal is determined as an audio mode; and an FD extension coder for performing extension coding on the high-frequency signal of the input signal when audio coding is performed on the LPC excitation signal.

50. The coding apparatus of claim 49, wherein the FD extension coder performs energy quantization by using a same codebook at different bitrates.

51. A decoding apparatus comprising: a mode information checking unit for checking mode information of each of frames included in a bitstream; a code excited linear prediction (CELP) decoder for performing CELP decoding on a CELP coded frame, based on a result of the checking; a time-domain (TD) extension decoder for generating a decoded signal of a high-frequency band by using at least one of a result of performing the CELP decoding and an excitation signal of a low-frequency signal; a frequency-domain (FD) decoder for performing FD decoding on an FD coded frame, based on the result of the checking; and an inverse frequency transformer for performing inverse frequency transformation on a result of performing the FD decoding.

52. The decoding apparatus of claim 51, wherein the FD decoder comprises: a normalization decoder for performing normalization decoding, based on normalization information included in the bitstream; a factorial pulse coding (FPC) decoder for performing FPC decoding, based on factorial pulse coding information included in the bitstream; and a noise filling performing unit for performing noise filling on a result of performing the FPC decoding.

53. The decoding apparatus of claim 51, wherein the FD decoder comprises: a normalization decoder for performing normalization decoding, based on normalization information included in the bitstream; a factorial pulse coding (FPC) decoder for performing FPC decoding, based on factorial pulse coding information included in the bitstream; a noise filling performing unit for performing noise filling on a result of performing the FPC decoding; and an FD high-frequency extension decoder for performing high-frequency extension decoding, based on the result of performing FPC decoding and a result of performing the noise filling.

54. The decoding apparatus of claim 52, wherein the FD decoder further comprises an FD low-frequency extension coder for performing extension coding on the results of performing the FPC decoding and the noise filling when an upper band value of a frequency band performing FPC decoding is less than an upper band value of a frequency band of a core signal.

55. The decoding apparatus of claim 52, wherein the FD high-frequency extension decoder performs inverse quantization of energy by sharing a same codebook at different bitrates.

56. The decoding apparatus of claim 51, wherein the FD decoder performs FD decoding on an FD coded frame, based on previous frame mode information included in the bitstream.

57. A decoding apparatus comprising: a mode information checking unit for checking mode information of each of frames included in a bitstream; a linear prediction coefficient (LPC) decoder for performing LPC decoding on the frames included in the bitstream; a code excited linear prediction (CELP) decoder for performing CELP decoding on a CELP coded frame, based an a result of the checking; a time-domain (TD) extension decoder for generating a decoded signal of a high-frequency band by using at least one of a result of performing the CELP decoding and an excitation signal of a low-frequency signal; an audio decoder for performing audio decoding on an audio coded frame, based on the result of the checking; and a frequency-domain (FD) extension decoder for performing extension decoding by using a result of performing the audio decoding.

58. The decoding apparatus of claim 57, wherein the FD extension decoder performs inverse quantization of energy by sharing a same codebook at different bitrates.

59. A coding method comprising; down-sampling an input signal; performing core coding on the down-sampled input signal; performing frequency transformation on the input signal; and performing bandwidth extension coding by using a base signal of the input signal in a frequency domain.

60. The coding method of claim 59, wherein the performing of the bandwidth extension coding comprises: generating the base signal of the input signal in the frequency domain by using a frequency spectrum of the input signal in the frequency domain; estimating an energy control factor by using the base signal; extracting energy from the input signal in the frequency domain; controlling the extracted energy by using the energy control factor; and quantizing the controlled energy.

61. The coding method of claim 60, wherein the generating of the base signal comprises: generating an artificial signal corresponding to a high-frequency band by copying and folding a low-frequency band of the input signal in the frequency domain; estimating an envelope of the base signal by using a window; and applying the estimated envelope to the artificial signal.

62. The coding method of claim 61, wherein a peak of the window corresponds to a frequency index for estimating the envelope of the base signal, and the estimating of the envelope of the base signal comprises estimating the envelope of the base signal by selecting a window according to comparison of a tonality or correlation.

63. The coding method of claim 61, wherein the estimating of the envelope of the base signal comprises estimating an average of frequency magnitudes of each of whitening bands as an envelope of a frequency belonging to the whitening band.

64. The coding method of claim 63, wherein the estimating of the envelope of the base signal comprises estimating the envelope of the base signal by controlling a number of frequency spectrums belonging to the whitening band according to a core coding mode.

65. The coding method of claim 60, wherein the estimating of the energy control factor comprises: calculating a tonality of a high-frequency band of the input signal in the frequency domain; calculating a tonality of the base signal; and calculating the energy control factor by using the tonality of the high-frequency band of the input signal and the tonality of the base signal.

66. The coding method of claim 60, wherein the controlling of the extracted energy comprises controlling energy of the input signal when the energy control factor is less than a predetermined threshold energy control factor.

67. The coding method of claim 60, wherein the quantizing of the controlled energy comprises selecting and quantizing a sub vector, and quantizing remaining sub vectors by using an interpolation error.

68. The coding method of claim 67, wherein the quantizing of the controlled energy comprises selecting a sub vector at a same time interval and performing quantization.

69. The coding method of claim 67, wherein the quantizing of the controlled energy comprises selecting candidates of the sub vector and performing multi-stage vector quantization using at least two stages.

70. The coding method of claim 69, wherein the quantizing of the controlled energy comprises generating an index set to satisfy mean square errors (MSEs) or weighted mean square errors (WMSESs) for each of the candidates of the sub vector in each of stages, and selecting a candidate of sub vector to minimize MSEs or WMSECs in all the stages from among the candidates.

71. The coding method of claim 69, wherein the quantizing of the controlled energy comprises generating an index set to minimize square errors (MSEs) or weighted mean square errors (WMSESs) for each of the candidates of the sub vector in each of stages, reconstructing energy vector through inverse quantization, and selecting a candidate of sub vector to minimize MSE or WMSEC between the reconstructed energy vector and the original energy vector from among the candidates.

72. A coding method comprising: down-sampling an input signal; performing core coding on the down-sampled input signal; performing frequency transformation on the input signal; and performing bandwidth extension coding by using characteristics of the input signal and a base signal of the input signal in a frequency domain.

73. The coding method of claim 72, wherein the performing of the bandwidth extension coding comprises: generating the base signal of the input signal in the frequency domain by using a frequency spectrum of the input signal in the frequency domain; estimating an energy control factor, based on the characteristics of the input signal and the base signal; extracting energy from the input signal in the frequency domain; controlling the extracted energy by using the energy control factor; and quantizing the controlled energy.

74. The coding method of claim 73, wherein the performing of the bandwidth extension coding further comprises classifying the input signal in the frequency domain according to characteristics of the input signal by using the frequency spectrum of the input signal in the frequency domain, and the estimating of the energy control factor comprises estimating the energy control factor by using the characteristics of the input signal which are determined in the classifying of the input signal according to the characteristics..

75. The coding method of claim 73, wherein the estimating of the energy control factor comprises estimating the energy control factor by using characteristics of the input signal, which are determined in the performing of the core coding.

76. The coding method of claim 73, wherein the generating of the base signal comprises: generating an artificial signal corresponding to a high-frequency band by copying and folding a low-frequency band of the input signal in the frequency domain; estimating an envelope of the base signal by using a window; and applying the estimated envelope to the artificial signal.

77. The coding method of claim 76, wherein a peak of the window corresponds to a frequency index for estimating the envelope of the base signal, and the estimating of the envelope of the base signal comprises estimating the envelope of the base signal by selecting a window according to comparison of a tonality or correlation. :

78. The coding method of claim 76, wherein the estimating of the envelope of the base signal comprises estimating an average of frequency magnitudes of each of whitening bands as an envelope of a frequency belonging to the whitening band.

79. The coding method of claim 78, wherein the estimating of the envelope of the base signal comprises estimating the envelope of the base signal by controlling a number of frequency spectrums belonging to the whitening band according to a core coding mode.

80. The coding method of claim 73, wherein the estimating of the energy control factor comprises: calculating a tonality of a high-frequency band of the input signal in the frequency domain; calculating a tonality of the base signal; and calculating the energy control factor by using the tonality of the high-frequency band of the input signal and the tonality of the base signal.

81. The coding method of claim 73, wherein the controlling of the extracted energy comprises controlling energy of the input signal when the energy control factor is less than a predetermined threshold energy control factor

82. The coding method of claim 73, wherein the quantizing of the controlled energy comprises selecting and quantizing a sub vector, and quantizing remaining sub vectors by using an interpolation error.

83. The coding method of claim 82, wherein the quantizing of the controlled energy comprises selecting a sub vector at a same time interval and performing quantization.

84. The coding method of claim 82, wherein the quantizing of the controlled energy comprises selecting candidates of the sub vector and performing multi-stage vector quantization using at least two stages.

85. A coding method comprising: extracting energy from an input signal in a frequency domain, based on a coding mode; controlling energy, based on the coding mode; and quantizing the energy, based on the coding mode.

86. A coding method comprising: selecting a coding mode of bandwidth extension coding by using an input signal in a frequency domain and an input signal in a time domain; and performing bandwidth extension coding by using the input signal in the frequency domain and the coding mode.

87. The coding method of claim 86, wherein the selecting of the coding mode comprises: classifying the input signal in the frequency domain by using the input signal in the frequency domain and the input signal in the time domain; and determining a coding mode of bandwidth extension coding according to the classified information, and determining a number of frequency bands according to the coding mode.

88. The coding method of claim 86, wherein the performing of the bandwidth extension coding comprises: extracting energy from the input signal in the frequency domain, based on the coding mode; controlling the extracted energy, based on the coding mode; and quantizing the controlled energy, based on the coding mode.

89. The coding method of claim 88, wherein the extracting of the energy from the input sighal comprises extracting energy corresponding to a frequency band, based on the coding mode.

90. The coding method of claim 88, wherein the controlling of the extracted energy comprises controlling the energy by using an energy control factor estimated according to a base signal of the input signal in the frequency domain.

91. The coding method of claim 88, wherein the quantizing of the controlled energy comprises performing quantization to be optimized for the input signal in the frequency domain, according to the coding mode.

92. The coding method of claim 21, wherein, if the coding mode is a transient mode, the quantizing of the controlled energy comprises quantizing energy of a frequency band by using a frequency weighting method.

93. The coding method of claim 92, wherein the frequency weighting method is a method for quantizing energy by assigning a weight to a low-frequency band of high perceptual importance.

94. The coding method of claim 91, wherein, if the coding mode is a normal mode or a harmonic mode, the quantizing of the controlled energy comprises quantizing energy of a frequency band by using an unequal bit allocation method.

95. The coding method of claim 94, wherein the unequal bit allocation method is a method of quantizing energy by assigning a larger number of bits to a low-frequency band of high perceptual importance than to a high-frequency band. :

96. The coding method of claim 88, wherein the quantizing of the controlled energy comprises predicting a representative value of a quantization target vector including at least two elements, and performing vector quantization on an error signal between each of the elements of the quantization target vector and the predicted representative value.

97. A decoding method comprising: performing core decoding on a core coded input signal included in a bitstream; up-sampling the core decoded input signal; performing frequency transformation on the up-sampled input signal; and performing bandwidth extension decoding by using an input signal in a frequency domain and energy of the input signal included in the bitstream.

98. The decoding method of claim 97, wherein the performing of the bandwidth extension decoding comprises: inversely quantizing the energy of the input signal; generating a base signal by using the input signal in the frequency domain; calculating a gain to be applied to the base signal by using the inversely quantized energy and energy of the base signal; and applying the gain to each of frequency bands.

99. The decoding method of claim 98, wherein the inverse quantizer selects and inversely quantizes a sub vector, interpolates the inversely quantized sub vector,', 'and inversely quantizes the energy by adding an interpolation error to the interpolated sub vector.100. The decoding method of claim 99, wherein the generating of the base signal comprises: generating an artificial signal corresponding t