Coding techniques using estimated spectral magnitude and phase derived from MDCT coefficients

Abstract

Estimates of spectral magnitude and phase are obtained by an estimation process using spectral information from analysis filter banks such as the Modified Discrete Cosine Transform. The estimation process may be implemented by convolution-like operations with impulse responses. Portions of the impulse responses may be selected for use in the convolution-like operations to trade off between computational complexity and estimation accuracy. Mathematical derivations of analytical expressions for filter structures and impulse responses are disclosed.

1. A method of processing information representing a source signal conveying content intended for human perception, the method comprising:
 receiving first spectral components that were generated by application of an analysis filterbank to the source signal, wherein the first spectral components represent spectral content of the source signal expressed in a first subspace of a multidimensional space; 
 deriving one or more first intermediate components from at least some of the first spectral components, wherein at least some of the first intermediate components differ from the first spectral components from which they are derived; 
 forming a combination of the one or more first intermediate components according to at least a portion of one or more impulse responses to obtain one or more second intermediate components; 
 deriving one or more second spectral components from the one or more second intermediate components, wherein the second spectral components represent spectral content of the source signal expressed in a second subspace of the multidimensional space that includes a portion of the multidimensional space not included in the first subspace; 
 obtaining estimated measures of magnitude or phase using the first spectral components and the second spectral components; and 
 applying an adaptive process to the first spectral components to generate processed informationgenerating encoded audio information using the first spectral components, wherein the adaptive processgenerating step is responsive to the estimated measures of magnitude or phase.;  
 wherein the method is performed by one or more computing devices. 
 
     
     
       2. The method of  claim 1 , wherein:
 the first spectral components are transform coefficients arranged in one or more blocks of transform coefficients that were generated by application of one or more transforms to one or more segments of the source signal; and 
 the portions of the one or more impulse responses are based on frequency response characteristics of the one or more transforms. 
 
     
     
       3. The method of  claim 2 , wherein the frequency response characteristics of the one or more transforms are dependent on characteristics of one or more analysis window functions that were applied with the one or more transforms to the one or more segments of the source signal. 
     
     
       4. The method of  claim 3 , wherein at least some of the one or more transforms implement an analysis filter bank that generates the first spectral components with time-domain aliasing. 
     
     
       5. The method of  claim 3 , wherein at least some of the one or more transforms generate first spectral components having real values expressed in the first subspace, and wherein the second spectral values have imaginary values expressed in the second subspace. 
     
     
       6. The method of  claim 5 , wherein the transforms that generate first spectral components having real values expressed in the first subspace are Discrete Cosine Transforms or Modified Discrete Cosine Transforms. 
     
     
       7. The method of  claim 1 , wherein:
 the first spectral components are transform coefficients arranged in one or more blocks of transform coefficients that were generated by application of one or more transforms to one or more segments of the source signal, 
 the one or more second intermediate components are obtained by combining the one or more first intermediate components according to a portion of the one or more impulse responses, each of the one or more impulse responses comprise a respective set of elements arranged in order, and 
 the portion of each of the one or more impulse responses excludes every other element in the respective set of elements. 
 
     
     
       8. The method according to  claim 1  that further comprises obtaining estimated measures of magnitude or phase using one or more third spectral components that are derived from at least some of the one or more first spectral components. 
     
     
       9. The method according to  claim 8 , wherein:
 the first spectral components are transform coefficients arranged in one or more blocks of transform coefficients that were generated by application of one or more transforms to one or more segments of the source signal; 
 the third spectral components are derived from a combination of two or more of the first spectral components; and 
 the estimated measures of magnitude or phase for a respective segment of the source signal are obtained adaptively using either the third spectral components or using the first and second spectral components. 
 
     
     
       10. The method according to  claim 8 , wherein:
 the first spectral components are transform coefficients arranged in one or more blocks of transform coefficients that were generated by application of one or more transforms to one or more segments of the source signal; 
 the third spectral components are derived from a combination of two or more of the first spectral components; and 
 the estimated measures of magnitude or phase for at least some spectral content of a respective segment of the source signal are obtained using the third spectral components and the estimated measures of magnitude or phase for at least some of the spectral content of the respective segment of the source signal are obtained using the first and second spectral components. 
 
     
     
       11. The method according to  claim 8  or  10  that comprises obtaining measures of magnitude or phase adaptively using either the third spectral components or using the first and second spectral components. 
     
     
       12. The method of  claim 1  that comprises adapting the portion of the one or more impulse responses in response to a measure of spectral component significance. 
     
     
       13. The method of  claim 12 , wherein the measure of spectral component significance is provided by a perceptual model that assesses perceptual significance of the spectral content of the source signal. 
     
     
       14. The method of  claim 12 , wherein the measure of spectral component significance reflects isolation in frequency of one or more spectral components. 
     
     
       15. The method of  claim 1 , wherein:
 the first spectral components are first transform coefficients arranged in one or more blocks that were generated by application of one or more transforms to one or more segments of the source signal, a respective block having a first number of first transform coefficients; 
 the second spectral components are second transform coefficients; 
 a second number of second transform coefficients are derived that represent spectral content that is also represented by some of the first transform coefficients in the respective block; and 
 the second number is less than the first number. 
 
     
     
       16. The method according to  claim 1 ,  2 ,  9 ,  10  or  12  that comprises:
 applying the adaptive process to the first spectral components to generate synthesized spectral components; 
 deriving one or more third intermediate components from the first spectral components and/or the second spectral components and from the synthesized spectral components; and 
 generating one or more output signals conveying content intended for human perception by applying one or more synthesis filterbanks to the one or more third intermediate components. 
 
     
     
       17. The method according to  claim 16 , wherein at least some of the synthesized spectral components are generated by spectral component regeneration. 
     
     
       18. The method according to  claim 16 , wherein at least some of the synthesized spectral components are generated by decomposition of first spectral components and/or second spectral components representing a composite of spectral content for a plurality of source signals. 
     
     
       19. The method according to  claim 16 , wherein at least some of the synthesized spectral components are generated by combining first spectral components and/or second spectral components to provide a composite representation of spectral content for a plurality of source signals. 
     
     
       20. The method according to  claim 1 ,  2 ,  9 ,  10  or  12  that comprises:
 generating the first spectral components by applying the analysis filter bank to the source signal; 
 applying the adaptive process to the first spectral component to generate encoded information representing at least some of the first spectral components; and 
 generating an output signal conveying the encoded information. 
 
     
     
       21. A non-transitory computer readable medium conveying a program of instructions that is executable by a device to perform a method of processing information representing a source signal conveying content intended for human perception, the method comprising:
 receiving first spectral components that were generated by application of an analysis filterbank to the source signal, wherein the first spectral components represent spectral content of the source signal expressed in a first subspace of a multidimensional space; 
 deriving one or more first intermediate components from at least some of the first spectral components, wherein at least some of the first intermediate components differ from the first spectral components from which they are derived; 
 forming a combination of the one or more first intermediate components according to at least a portion of one or more impulse responses to obtain one or more second intermediate components; 
 deriving one or more second spectral components from the one or more second intermediate components, wherein the second spectral components represent spectral content of the source signal expressed in a second subspace of the multidimensional space that includes a portion of the multidimensional space not included in the first subspace; 
 obtaining estimated measures of magnitude or phase using the first spectral components and the second spectral components; and 
 applying an adaptive process to the first spectral components to generate processed informationgenerating encoded audio information using the first spectral components, wherein the adaptive processgenerating step is responsive to the estimated measures of magnitude or phase. 
 
     
     
       22. The medium of  claim 21 , wherein:
 the first spectral components are transform coefficients arranged in one or more blocks of transform coefficients that were generated by application of one or more transforms to one or more segments of the source signal; and 
 the portions of the one or more impulse responses are based on frequency response characteristics of the one or more transforms, which are dependent on characteristics of one or more analysis window functions that were applied with the one or more transforms to the one or more segments of the source signal. 
 
     
     
       23. The medium according to  claim 21 , wherein the method further comprises obtaining estimated measures of magnitude or phase using one or more third spectral components that are derived from at least some of the one or more first spectral components. 
     
     
       24. The medium according to  claim 23 , wherein:
 the first spectral components are transform coefficients arranged in one or more blocks of transform coefficients that were generated by application of one or more transforms to one or more segments of the source signal; 
 the third spectral components are derived from a combination of two or more of the first spectral components; and 
 the estimated measures of magnitude or phase for a respective segment of the source signal are obtained adaptively using either the third spectral components or using the first and second spectral components. 
 
     
     
       25. The medium according to  claim 23 , wherein:
 the first spectral components are transform coefficients arranged in one or more blocks of transform coefficients that were generated by application of one or more transforms to one or more segments of the source signal; 
 the third spectral components are derived from a combination of two or more of the first spectral components; and 
 the estimated measures of magnitude or phase for at least some spectral content of a respective segment of the source signal are obtained using the third spectral components and the estimated measures of magnitude or phase for at least some of the spectral content of the respective segment of the source signal are obtained using the first and second spectral components. 
 
     
     
       26. The medium according to  claim 23 , wherein the method comprises obtaining measures of magnitude or phase adaptively using either the third spectral components or using the first and second spectral components. 
     
     
       27. The medium of  claim 21 , wherein the method comprises adapting the portion of the one or more impulse responses in response to a measure of spectral component significance. 
     
     
       28. The medium of  claim 27 , wherein the measure of spectral component significance is provided by a perceptual model that assesses perceptual significance of the spectral content of the source signal. 
     
     
       29. The medium of  claim 27 , wherein the measure of spectral component significance reflects isolation in frequency of one or more spectral components. 
     
     
       30. The medium of  claim 21 , wherein:
 the first spectral components are first transform coefficients arranged in one or more blocks that were generated by application of one or more transforms to one or more segments of the source signal, a respective block having a first number of first transform coefficients; 
 the second spectral components are second transform coefficients; 
 a second number of second transform coefficients are derived that represent spectral content that is also represented by some of the first transform coefficients in the respective block; and 
 the second number is less than the first number. 
 
     
     
       31. The medium according to  claim 21 , wherein the method comprises:
 applying the adaptive process to the first spectral components to generate synthesized spectral components; 
 deriving one or more third intermediate components from the first spectral components and/or the second spectral components and from the synthesized spectral components; and 
 generating one or more output signals conveying content intended for human perception by applying one or more synthesis filterbanks to the one or more third intermediate components. 
 
     
     
       32. The medium according to  claim 21 , wherein the method comprises:
 generating the first spectral components by applying the analysis filter bank to the source signal; 
 applying the adaptive process to the first spectral component to generate encoded information representing at least some of the first spectral components; and 
 generating an output signal conveying the encoded information. 
 
     
     
       33. An apparatus for processing information representing a source signal conveying content intended for human perception, the apparatus comprising:
 means for receiving first spectral components that were generated by application of an analysis filterbank to the source signal, wherein the first spectral components represent spectral content of the source signal expressed in a first subspace of a multidimensional space; 
 means for deriving one or more first intermediate components from at least some of the first spectral components, wherein at least some of the first intermediate components differ from the first spectral components from which they are derived; means for forming a combination of the one or more first intermediate components according to at least a portion of one or more impulse responses to obtain one or more second intermediate components; 
 means for deriving one or more second spectral components from the one or more second intermediate components, wherein the second spectral components represent spectral content of the source signal expressed in a second subspace of the multidimensional space that includes a portion of the multidimensional space not included in the first subspace; 
 means for obtaining estimated measures of magnitude or phase using the first spectral components and the second spectral components; and 
 means for applying an adaptive process to the first spectral components to generate processed information generating encoded audio information using the first spectral components, wherein the adaptive process generating means is responsive to the estimated measures of magnitude or phase. 
 
     
     
       34. The apparatus of  claim 33 , wherein:
 the first spectral components are transform coefficients arranged in one or more blocks of transform coefficients that were generated by application of one or more transforms to one or more segments of the source signal; and 
 the portions of the one or more impulse responses are based on frequency response characteristics of the one or more transforms, which are dependent on characteristics of one or more analysis window functions that were applied with the one or more transforms to the one or more segments of the source signal. 
 
     
     
       35. The apparatus according to  claim 33  that further comprises means for obtaining estimated measures of magnitude or phase using one or more third spectral components that are derived from at least some of the one or more first spectral components. 
     
     
       36. The apparatus according to  claim 35  wherein:
 the first spectral components are transform coefficients arranged in one or more blocks of transform coefficients that were generated by application of one or more transforms to one or more segments of the source signal; 
 the third spectral components are derived from a combination of two or more of the first spectral components; and 
 the estimated measures of magnitude or phase for a respective segment of the source signal are obtained adaptively using either the third spectral components or using the first and second spectral components. 
 
     
     
       37. The apparatus according to  claim 35 , wherein:
 the first spectral components are transform coefficients arranged in one or more blocks of transform coefficients that were generated by application of one or more transforms to one or more segments of the source signal; 
 the third spectral components are derived from a combination of two or more of the first spectral components; and 
 the estimated measures of magnitude or phase for at least some spectral content of a respective segment of the source signal are obtained using the third spectral components and the estimated measures of magnitude or phase for at least some of the spectral content of the respective segment of the source signal are obtained using the first and second spectral components. 
 
     
     
       38. The apparatus according to  claim 35  that comprises means for obtaining measures of magnitude or phase adaptively using either the third spectral components or using the first and second spectral components. 
     
     
       39. The apparatus of  claim 33  that comprises means for adapting the portion of the one or more impulse responses in response to a measure of spectral component significance. 
     
     
       40. The apparatus of  claim 39 , wherein the measure of spectral component significance is provided by a perceptual model that assesses perceptual significance of the spectral content of the source signal. 
     
     
       41. The apparatus of  claim 39 , wherein the measure of spectral component significance reflects isolation in frequency of one or more spectral components. 
     
     
       42. The apparatus of  claim 33 , wherein:
 the first spectral components are first transform coefficients arranged in one or more blocks that were generated by application of one or more transforms to one or more segments of the source signal, a respective block having a first number of first transform coefficients; 
 the second spectral components are second transform coefficients; 
 a second number of second transform coefficients are derived that represent spectral content that is also represented by some of the first transform coefficients in the respective block; and 
 the second number is less than the first number. 
 
     
     
       43. The apparatus according to  claim 33  that comprises:
 means for applying the adaptive process to the first spectral components to generate synthesized spectral components; 
 means for deriving one or more third intermediate components from the first spectral components and/or the second spectral components and from the synthesized spectral components; and 
 means for generating one or more output signals conveying content intended for human perception by applying one or more synthesis filterbanks to the one or more third intermediate components. 
 
     
     
       44. The apparatus according to  claim 33  that comprises:
 means for generating the first spectral components by applying the analysis filter bank to the source signal; 
 means for applying the adaptive process to the first spectral component to generate encoded information representing at least some of the first spectral components; and 
 means for generating an output signal conveying the encoded information. 
 
     
     
       45. A method of processing information representing a source signal conveying content intended for human perception, the method comprising:
 receiving first spectral components that were generated by application of a first analysis filterbank to the source signal;   obtaining second spectral components from a convolution of a derivation of at least some of the first spectral components in two or more segments with a portion of one or more impulse responses of hypothetical filters related to the combined effect of a synthesis filterbank inverse to the first analysis filterbank and a second analysis filterbank coupled to the synthesis filterbank;   obtaining estimated measures of magnitude or phase using the first spectral components and the second spectral components; and   generating encoded audio information using the first spectral components, wherein the generating step is responsive to the estimated measures of magnitude or phase;   wherein the method is performed by one or more computing devices.   
     
     
       46. The method of claim 45, wherein:
 the first spectral components are transform coefficients arranged in one or more blocks of transform coefficients that were generated by application of one or more transforms to one or more segments of the source signal; and   the portions of the one or more impulse responses are based on frequency response characteristics of the one or more transforms.   
     
     
       47. The method of claim 46, wherein the frequency response characteristics of the one or more transforms are dependent on characteristics of one or more analysis window functions that were applied with the one or more transforms to the one or more segments of the source signal. 
     
     
       48. The method of claim 47, wherein at least some of the one or more transforms implement an analysis filter bank that generates the first spectral components with time-domain aliasing. 
     
     
       49. The method of claim 47, wherein at least some of the one or more transforms generate first spectral components having real values and wherein the second spectral values have imaginary values. 
     
     
       50. The method of claim 49, wherein the transforms that generate first spectral components having real values are Discrete Cosine Transforms or Modified Discrete Cosine Transforms. 
     
     
       51. The method according to claim 45 that further comprises obtaining estimated measures of magnitude or phase using one or more third spectral components that are derived from at least some of the one or more first spectral components. 
     
     
       52. The method according to claim 51, wherein:
 the first spectral components are transform coefficients arranged in one or more blocks of transform coefficients that were generated by application of one or more transforms to one or more segments of the source signal;   the third spectral components are derived from a combination of two or more of the first spectral components; and   the estimated measures of magnitude or phase for a respective segment of the source signal are obtained adaptively using either the third spectral components or using the first and second spectral components.   
     
     
       53. The method according to claim 51, wherein:
 the first spectral components are transform coefficients arranged in one or more blocks of transform coefficients that were generated by application of one or more transforms to one or more segments of the source signal;   the third spectral components are derived from combination of two or more of the first spectral components; and   the estimated measures of magnitude or phase for at least some spectral content of a respective segment of the source signal are obtained using the third spectral components and the estimated measures of magnitude or phase for at least some of the spectral content of the respective segment of the source signal obtained using the first and second spectral components.   
     
     
       54. The method according to claim 51 or 53 that comprises obtaining measures of magnitude or phase adaptively using either the third spectral components or using the first and second spectral components. 
     
     
       55. The method of claim 45 that comprises adapting the portion of the one or more impulse responses in response to a measure of spectral component significance. 
     
     
       56. The method of claim 45, wherein the measure of spectral component significance is provided by a perceptual model that assesses perceptual significance of the spectral content of the source signal. 
     
     
       57. The method of claim 45, wherein the measure of spectral component significance reflects isolation in frequency of one or more spectral components. 
     
     
       58. The method of claim 45, wherein:
 the first spectral components are first transform coefficients arranged in one or more blocks that were generated by application of one or more transforms to one or more segments of the source signal, a respective block having a first number of first transform coefficients;   the second spectral components are second transform coefficients;   a second number of second transform coefficients are derived that represent spectral content that is also represented by some of the first transform coefficients in the respective block; and   the second number is less than the first number.   
     
     
       59. The method according to claim 45, 46, 52, 53 or 55 that comprises applying the adaptive process to the first spectral components to generate synthesized spectral components. 
     
     
       60. The method according to claim 59, wherein at least some of the synthesized spectral components are generated by spectral component regeneration. 
     
     
       61. The method according to claim 59, wherein at least some of the synthesized spectral components are generated by decomposition of first spectral components and/or second spectral components representing a composite of spectral content for a plurality of source signals. 
     
     
       62. The method according to claim 59, wherein at least some of the synthesized spectral components are generated by combining first spectral components and/or second spectral components to provide a composite representation of spectral content for a plurality of source signals. 
     
     
       63. The method according to claim 45, 46, 52, 53 or 55 that comprises:
 generating the first spectral components by applying the analysis filterbank to the source signal;   applying the adaptive process to the first spectral component to generate encoded information representing at least some of first spectral components; and   generating an output signal conveying the encoded information.   
     
     
       64. A method of processing information representing a source signal conveying content intended for human perception, the method comprising:
 receiving first spectral components that were generated by application of a first analysis filterbank to the source signal;   obtaining second spectral components from a convolution of a derivation of at least some of the first spectral components with a portion of one or more impulse responses of hypothetical filters related to the combined effect of a synthesis filterbank inverse to the first analysis filterbank and a second analysis filterbank coupled to the synthesis filterbank;   obtaining estimated measures of magnitude or phase using the first spectral components and the second spectral components; and   generating encoded audio information using the first spectral components, wherein the generating step is responsive to the estimated measures of magnitude or phase;   wherein the method is performed by one or more computing devices.   
     
     
       65. The method of claim 64, wherein:
 the first spectral components are transform coefficients arranged in one or more blocks of transform coefficients that were generated by application of one or more transforms to one or more segments of the source signal; and   the portions of the one or more impulse responses are based on frequency response characteristics of the one or more transforms.   
     
     
       66. The method of claim 65, wherein the frequency response characteristics of the one or more transforms are dependent on characteristics of one or more analysis window functions that were applied with the one or more transforms to the one or more segments of the source signal. 
     
     
       67. The method of claim 66, wherein at least some of the one or more transforms implement an analysis filter bank that generates the first spectral components with time-domain aliasing. 
     
     
       68. The method of claim 66, wherein at least some of the one or more transforms generate first spectral components having real values and wherein the second spectral values have imaginary values. 
     
     
       69. The method of claim 68, wherein the transforms that generate first spectral components having real values are Discrete Cosine Transforms or Modified Discrete Cosine Transforms. 
     
     
       70. The method according to claim 64 that further comprises obtaining estimated measures of magnitude or phase using one or more third spectral components that are derived from at least some of the one or more first spectral components. 
     
     
       71. The method according to claim 70, wherein:
 the first spectral components are transform coefficients arranged in one or more blocks of transform coefficients that were generated by application of one or more transforms to one or more segments of the source signal;   the third spectral components are derived from a combination of two or more of the first spectral components; and   the estimated measures of magnitude or phase are obtained adaptively using either the third spectral components or using the first and second spectral components.   
     
     
       72. The method according to claim 70 wherein:
 the first spectral components are transform coefficients arranged in one or more blocks of transform coefficients that were generated by application of one or more transforms to one or more segments of the source signal;   the third spectral components are derived from combination of two or more of the first spectral components; and   the estimated measures of magnitude or phase for at least some spectral content of the source signal are obtained using the third spectral components and the estimated measures of magnitude or phase for at least some of the spectral content of the respective segment of the source signal obtained using the first and second spectral components.   
     
     
       73. The method according to claim 70 or 72 that comprises obtaining measures of magnitude or phase adaptively using either the third spectral components or using the first and second spectral components. 
     
     
       74. The method of claim 64 that comprises adapting the portion of the one or more impulse responses in response to a measure of spectral component significance. 
     
     
       75. The method of claim 64, wherein the measure of spectral component significance is provided by a perceptual model that assesses perceptual significance of the spectral content of the source signal. 
     
     
       76. The method of claim 64, wherein the measure of spectral component significance reflects isolation in frequency of one or more spectral components. 
     
     
       77. The method of claim 64, wherein:
 the first spectral components are first transform coefficients arranged in one or more blocks that were generated by application of one or more transforms of the source signal, a respective block having a first number of first transform coefficients;   the second spectral components are second transform coefficients;   a second number of second transform coefficients are derived that represent spectral content that is also represented by some of the first transform coefficients in the respective block; and   the second number is less than the first number.   
     
     
       78. The method according to claim 64, 65, 71, 72 or 74 that comprises applying the adaptive process to the first spectral components to generate synthesized spectral components. 
     
     
       79. The method according to claim 78, wherein at least some of the synthesized spectral components are generated by spectral component regeneration. 
     
     
       80. The method according to claim 78, wherein at least some of the synthesized spectral components are generated by decomposition of first spectral components and/or second spectral components representing a composite of spectral content for a plurality of source signals. 
     
     
       81. The method according to claim 78, wherein at least some of the synthesized spectral components are generated by combining first spectral components and/or second spectral components to provide a composite representation of spectral content for a plurality of source signals. 
     
     
       82. The method according to claim 64, 65, 66, 72 or 74 that comprises:
 generating the first spectral components by applying the analysis filterbank to the source signal;   applying the adaptive process to the first spectral component to generate encoded information representing at least some of first spectral components; and   generating an output signal conveying the encoded information.   
     
     
       83. A method of processing information representing a source signal conveying content intended for human perception, the method comprising:
 receiving first spectral components that were generated by application of a first analysis filterbank to the source signal;   obtaining second spectral components from a convolution of a derivation of at least some of the first spectral components with a portion of one or more impulse responses of hypothetical filters related to the combined effect of a synthesis filterbank inverse to the first analysis filterbank and a second analysis filterbank coupled to the synthesis filterbank;   obtaining estimated parameters using the first spectral components and the second spectral components; and   generating encoded audio information using the first spectral components, wherein the generating step is responsive to the estimated measures of magnitude or phase;   wherein the method is performed by one or more computing devices.   
     
     
       84. The method of claim 83, wherein:
 the first spectral components are transform coefficients arranged in one or more blocks of transform coefficients that were generated by application of one or more transforms to one or more segments of the source signal; and   the portions of the one or more impulse responses are based on frequency response characteristics of the one or more transforms.   
     
     
       85. The method of claim 84, wherein the frequency response characteristics of the one or more transforms are dependent on characteristics of one or more analysis window functions that were applied with the one or more transforms to the one or more segments of the source signal. 
     
     
       86. The method of claim 85, wherein at least some of the one or more transforms implement an analysis filter bank that generates the first spectral components with time-domain aliasing. 
     
     
       87. The method of claim 85, wherein at least some of the one or more transforms generate first spectral components having real values and wherein the second spectral values have imaginary values. 
     
     
       88. The method of claim 87, wherein the transforms that generate first spectral components having real values are Discrete Cosine Transforms or Modified Discrete Cosine Transforms. 
     
     
       89. The method according to claim 85, wherein the estimated parameters are estimated measures of magnitude or phase, further comprising obtaining estimated measures of magnitude or phase using one or more third spectral components that are derived from at least some of the one or more first spectral components. 
     
     
       90. The method according to claim 89, wherein:
 the first spectral components are transform coefficients arranged in one or more blocks of transform coefficients that were generated by application of one or more transforms to one or more segments of the source signal;   the third spectral components are derived from a combination of two or more of the first spectral components; and   the estimated measures of magnitude or phase are obtained adaptively using either the third spectral components or using the first and second spectral components.   
     
     
       91. The method according to claim 89, wherein:
 the first spectral components are transform coefficients arranged in one or more blocks of transform coefficients that were generated by application of one or more transforms to one or more segments of the source signal;   the third spectral components are derived from combination of two or more of the first spectral components; and   the estimated measures of magnitude or phase for at least some spectral content of the source signal are obtained using the third spectral components and the estimated measures of magnitude or phase for at least some of the spectral content of the respective segment of the source signal obtained using the first and second spectral components.   
     
     
       92. The method according to claim 89 or 91 that comprises obtaining measures of magnitude or phase adaptively using either the third spectral components or using the first and second spectral components. 
     
     
       93. The method of claim 83 that comprises adapting the portion of the one or more impulse responses in response to a measure of spectral component significance. 
     
     
       94. The method of claim 83, wherein the measure of spectral component significance is provided by a perceptual model that assesses perceptual significance of the spectral content of the source signal. 
     
     
       95. The method of claim 83, wherein the measure of spectral component significance reflects isolation in frequency of one or more spectral components. 
     
     
       96. The method of claim 83, wherein:
 the first spectral components are first transform coefficients arranged in one or more blocks that were generated by application of one or more transforms of the source signal, a respective block having a first number of first transform coefficients;   the second spectral components are second transform coefficients;   a second number of second transform coefficients are derived that represent spectral content that is also represented by some of the first transform coefficients in the respective block; and   the second number is less than the first number.   
     
     
       97. The method according to claim 83, 84, 90, 91 or 93 that comprises applying the adaptive process to the first spectral components to generate synthesized spectral components. 
     
     
       98. The method according to claim 97, wherein at least some of the synthesized spectral components are generated by spectral component regeneration. 
     
     
       99. The method according to claim 97, wherein at least some of the synthesized spectral components are generated by decomposition of first spectral components and/or second spectral components representing a composite of spectral content for a plurality of source signals. 
     
     
       100. The method according to claim 97, wherein at least some of the synthesized spectral components are generated by combining first spectral components and/or second spectral components to provide a composite representation of spectral content for a plurality of source signals. 
     
     
       101. The method according to claim 83, 84, 90, 91 or 93 that comprises:
 generating the first spectral components by applying the analysis filterbank to the source signal;   applying the adaptive process to the first spectral component to generate encoded information representing at least some of first spectral components; and   generating an output signal conveying the encoded information.