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Methods, apparatus and articles of manufacture for mixing compressed digital bit streams are disclosed. An example method disclosed herein comprises acquiring a frame associated with a first compressed digital bit stream, unpacking the frame to obtain a plurality of original transform coefficient se

Methods, apparatus and articles of manufacture for mixing compressed digital bit streams are disclosed. An example method disclosed herein comprises acquiring a frame associated with a first compressed digital bit stream, unpacking the frame to obtain a plurality of original transform coefficient sets, and modifying the plurality of original transform coefficient sets to mix a second digital bit stream with the first compressed digital bit stream.

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1. A method of mixing a first compressed digital bit stream with a second digital bit stream, the method comprising: acquiring a frame associated with the first compressed digital bit stream;unpacking the frame to obtain a plurality of original transform coefficient sets; andmodifying the plurality

1. A method of mixing a first compressed digital bit stream with a second digital bit stream, the method comprising: acquiring a frame associated with the first compressed digital bit stream;unpacking the frame to obtain a plurality of original transform coefficient sets; andmodifying the plurality of original transform coefficient sets to mix the second digital bit stream with the first compressed digital bit stream, wherein modifying the plurality of original transform coefficient sets comprises:determining a first mantissa code associated with a mixed transform coefficient of one of a plurality of mixed transform coefficient sets; andsubstituting the first mantissa code associated with the mixed transform coefficient for a second mantissa code associated with a corresponding original transform coefficient of one of the plurality of original transform coefficient sets. 2. A method as defined in claim 1 wherein determining the first mantissa code associated with the mixed transform coefficient of the one of the plurality of mixed transform coefficient sets comprises: determining a quantization step size associated with the corresponding original transform coefficient of one of the plurality of original transform coefficient sets;generating the mixed transform coefficient based on combining an element associated with the first compressed digital bit stream and an element associated with the second digital bit stream;quantizing the mixed transform coefficient based on the quantization step size to generate a quantized mantissa; anddetermining the first mantissa code associated with the mixed transform coefficient based on the quantized mantissa. 3. A method as defined in claim 2 wherein the quantization step size is based on an exponent associated with the corresponding original transform coefficient. 4. A method as defined in claim 2 wherein combining the element associated with the first compressed digital bit stream and the element associated with the second digital bit stream comprises adding the element associated with the first compressed digital bit stream and the element associated with the second digital bit stream. 5. A method as defined in claim 4 further comprising attenuating at least one of the element of the first compressed digital bit stream or the element of the second digital bit stream prior to adding the element of the first compressed digital bit stream and the element of the second digital bit stream. 6. A method as defined in claim 1 wherein modifying the plurality of original transform coefficient sets comprises: generating a plurality of time-domain audio blocks based on the plurality of original transform coefficient sets;generating a plurality of reconstructed audio blocks based on the plurality of time-domain audio blocks; andgenerating a plurality of mixed audio blocks based on the plurality of reconstructed audio blocks and the second digital bit stream. 7. A method as defined in claim 6 wherein generating the plurality of reconstructed audio blocks based on the plurality of time-domain audio blocks comprises generating a reconstructed time-domain audio block based on a first time-domain audio block and a second time-domain audio block. 8. A method as defined in claim 7 wherein generating the reconstructed time-domain audio block based on the first time-domain audio block and the second time-domain audio block comprises adding the first and second time-domain audio blocks. 9. A method as defined in claim 1 further comprising generating the plurality of mixed coefficient sets by determining mantissa codes associated with mixed transform coefficients of each of the plurality mixed transform coefficient sets based on compression information associated with the first compressed digital bit stream. 10. A method as defined in claim 1 wherein each of the plurality of original transform coefficient sets comprises one or more modified discrete cosine transform coefficients. 11. A method as defined in claim 1 wherein the first compressed digital bit stream is compressed in accordance with an audio compression standard. 12. A method as defined in claim 1 wherein acquiring the frame associated with the first compressed digital bit stream comprises acquiring audio blocks associated with at least one of a plurality of audio channels. 13. A method as defined in claim 1 wherein unpacking the frame to obtain the plurality of original transform coefficient sets comprises determining compression information associated with the first compressed digital bit stream. 14. A method as defined in claim 1 further comprising repacking the frame based on a plurality of mixed transform coefficient sets. 15. A method as defined in claim 1 wherein the first compressed digital bit stream corresponds to a main audio service and the second digital bit stream corresponds to an auxiliary audio service. 16. A method as defined in claim 1 wherein the second digital bit stream is compressed. 17. A method as defined in claim 16 wherein a pseudo-noise signal is added to the second digital bit stream prior to compression. 18. A method of mixing a first compressed digital bit stream with a second digital bit stream, the method comprising: acquiring a frame associated with the first compressed digital bit stream;unpacking the frame to obtain a plurality of original transform coefficient sets; andmodifying the plurality of original transform coefficient sets to mix the second digital bit stream with the first compressed digital bit stream, wherein the second digital bit stream is compressed, a pseudo-noise signal is added to the second digital bit stream prior to compression, and modifying the plurality of original transform coefficient sets comprises:determining a first mantissa code associated with a pseudo-noise transform coefficient of one of a plurality of pseudo-noise transform coefficient sets; andmodifying a second mantissa code associated with a corresponding original transform coefficient of one of the plurality of original transform coefficient sets based on the first mantissa code. 19. A method as defined in claim 18 wherein the plurality of pseudo-noise transform coefficient sets are determined based on an average spectral characteristic of the pseudo-noise signal. 20. A data stream mixing apparatus comprising: an acquisition unit to acquire a frame associated with a first compressed digital data stream;an unpacking unit to unpack the frame to obtain a plurality of original transform coefficient sets; anda modification unit comprising a processor to modify the plurality of original transform coefficient sets to mix a second digital data stream with the first compressed digital data stream, wherein the modification unit is to:determine a first mantissa code associated with a mixed transform coefficient of one of a plurality of mixed transform coefficient sets; andsubstitute the first mantissa code associated with the mixed transform coefficient for a second mantissa code associated with a corresponding original transform coefficient of one of the plurality of transform coefficient sets. 21. An apparatus as defined in claim 20 wherein the modification unit is to: determine a quantization step size associated with the corresponding original transform coefficient of one of the plurality of original transform coefficient sets;generate the mixed transform coefficient based on a combination of an element associated with the first compressed digital data stream and an element associated with the second digital data stream;quantize the mixed transform coefficient based on the quantization step size to generate a quantized mantissa; anddetermine the first mantissa code associated with the mixed transform coefficient based on the quantized mantissa. 22. An apparatus as defined in claim 21 wherein the quantization step size is based on an exponent associated with the corresponding original transform coefficient. 23. An apparatus as defined in claim 21 wherein the combination of the element associated with the first compressed digital data stream and the element associated with the second digital data stream comprises the addition of the element associated with the first compressed digital data stream and the element associated with the second digital data stream. 24. An apparatus as defined in claim 23 wherein the combination of the element associated with the first compressed digital data stream and the element associated with the second digital data stream further comprises the attenuation of at least one of the element associated with the first compressed digital data stream or the element associated with the second digital data stream prior to the addition of the element associated with the first compressed digital data stream and the element associated with the second digital data stream. 25. An apparatus as defined in claim 20 wherein the modification unit is to: generate a plurality of time-domain audio blocks based on the original transform coefficient sets;generate a plurality of reconstructed audio blocks based on the plurality of time-domain audio blocks; andgenerate a plurality of mixed audio blocks based on the plurality of reconstructed audio blocks and the second digital data stream. 26. An apparatus as defined in claim 25 wherein the modification unit is to generate a reconstructed time-domain audio block in the plurality of reconstructed audio blocks based on a first time-domain audio block and a second time-domain audio block in the plurality of time-domain audio blocks. 27. An apparatus as defined in claim 26 wherein the modification unit is to add the first and second time-domain audio blocks to generate the reconstructed time-domain audio block. 28. An apparatus as defined in claim 20 wherein the modification unit is further to generate the plurality of mixed transform coefficient sets based on the second digital data stream and compression information associated with the first compressed digital data stream. 29. An apparatus as defined in claim 20 wherein each of the plurality of original transform coefficient sets comprises one or more modified discrete cosine transform coefficients. 30. An apparatus as defined in claim 20 wherein the first compressed digital data stream is compressed in accordance with an audio compression standard. 31. An apparatus as defined in claim 20 wherein the acquisition unit is to acquire audio blocks associated with a plurality of audio channels. 32. An apparatus as defined in claim 20 wherein the unpacking unit is to obtain compression information associated with the first compressed digital data stream. 33. An apparatus as defined in claim 20 wherein the first compressed digital data stream is associated with a main audio service and the second digital data stream is associated with an auxiliary audio service. 34. An apparatus as defined in claim 20 further comprising a repacking unit to repack the frame based on a plurality of mixed transform coefficient sets. 35. A tangible machine readable storage medium comprising instructions which, when executed, cause a machine to: acquire a frame associated with a first compressed digital bit stream;unpack the frame to obtain a plurality of original transform coefficient sets; andmodify the plurality of original transform coefficient sets to mix a second digital bit stream with the first compressed digital bit stream, wherein the instructions, when executed, cause the machine to modify the plurality of original transform coefficient sets by:determining a first mantissa code associated with a mixed transform coefficient of one of a plurality of mixed transform coefficient sets; andsubstituting the first mantissa code associated with the mixed transform coefficient for a second mantissa code associated with a corresponding original transform coefficient of one of the plurality of original transform coefficient sets. 36. A storage medium as defined in claim 35 wherein the instructions, when executed, cause the machine to determine the first mantissa code associated with the mixed transform coefficient of the one of the plurality of mixed transform coefficient sets by: determining a quantization step size associated with the corresponding original transform coefficient of one of the plurality of original transformed coefficient sets;generating the mixed transform coefficient based on combining an element associated with the first compressed digital bit stream and an element associated with the second digital bit stream;quantizing the mixed transform coefficient based on the quantization step size to generate a quantized mantissa; anddetermining the first mantissa code associated with the mixed transform coefficient based on the quantized mantissa. 37. A storage medium as defined in claim 35 wherein the instructions, when executed, cause the machine to modify the plurality of original transform coefficient sets by: generating a plurality of time-domain audio blocks based on the plurality of original transform coefficient sets;generating a plurality of reconstructed audio blocks based on the plurality of time-domain audio blocks; andgenerating a plurality of mixed audio blocks based on the plurality of reconstructed audio blocks and the second digital bit stream. 38. A storage medium as defined in claim 35 wherein the instructions, when executed, further cause the machine to generate the plurality of mixed coefficient sets by determining mantissa codes associated with mixed transform coefficients of each of the plurality of mixed coefficient sets based on compression information associated with the first compressed digital bit stream. 39. A storage medium as defined in claim 35 wherein the instructions, when executed, further cause the machine to acquire the frame associated with the first compressed digital bit stream by acquiring audio blocks associated with at least one of a plurality of audio channels. 40. A storage medium as defined in claim 35 wherein the instructions, when executed, cause the machine to unpack the frame to obtain the plurality of original transform coefficient sets by identifying compression information associated with the first compressed digital bit stream. 41. A storage medium as defined in claim 35 wherein the instructions, when executed, further cause the machine to repack the frame based on a plurality of mixed transform coefficient sets. 42. A storage medium as defined in claim 35 wherein the first compressed digital bit stream is associated with a main audio service and the second digital bit stream is associated with an auxiliary audio service. 43. A system to mix digital data streams comprising a first source to provide a first compressed digital data stream;a second source to provide a second digital data stream; anda mixing device comprising a processor to mix the second digital data stream with the first compressed digital data stream without uncompressing the first compressed digital data stream, wherein the first compressed digital data stream comprises a plurality of original transform coefficients, and the mixing device is to modify the plurality of original transform coefficient sets to mix the second digital data stream with the first compressed digital data stream by:determining a first mantissa code associated with a mixed transform coefficient of one of a plurality of mixed transform coefficient sets; andsubstituting the first mantissa code associated with the mixed transform coefficient for a second mantissa code associated with a corresponding original transform coefficient of one of a plurality of transform coefficient sets. 44. A system as defined in claim 43 wherein the plurality of original transform coefficients comprises respective pluralities of original mantissas and original exponents, and the mixing device is to modify only the plurality of original mantissas to modify the plurality of original transform coefficients. 45. A system as defined in claim 44 wherein the mixing device is to modify the plurality of original transform coefficients by determining the plurality of mixed transform coefficients based on the second digital data stream and compression information associated with the first compressed digital data stream. 46. A system as defined in claim 45 wherein the compression information comprises at least one quantization step size. 47. A system as defined in claim 45 wherein determining the plurality of mixed transform coefficients comprises quantizing a plurality of mixed mantissas associated with the mixed transform coefficients. 48. A system as defined in claim 47 wherein the mixing device is to modify the plurality of original mantissas based on the plurality of quantized mixed mantissas and the compression information. 49. A system as defined in claim 43 wherein the first compressed digital data stream is compressed according to an audio compression standard. 50. A system as defined in claim 43 wherein the first compressed digital data stream is associated with a main audio service and the second digital data stream is associated with an auxiliary data service. 51. A system as defined in claim 43 wherein the second digital data stream is uncompressed. 52. A method as of combining a first compressed digital data stream with a second digital data stream, the method comprising: acquiring a frame associated with the first compressed digital data stream;unpacking the frame to obtain a plurality of original transform coefficient sets; andmodifying the plurality of original transform coefficient sets to combine the second digital data stream with the first compressed digital data stream, wherein modifying the plurality of original transform coefficient sets comprises:determining a first mantissa code associated with a mixed transform coefficient of one of a plurality of mixed transform coefficient sets; andsubstituting the first mantissa code associated with the mixed transform coefficient for a second mantissa code associated with a corresponding original transform coefficient of one of the plurality of original transform coefficient sets. 53. A method as defined in claim 52 wherein combining comprises mixing and wherein modifying the plurality of original transform coefficient sets to combine the second digital data stream with the first compressed digital data stream comprises modifying the plurality of original transform coefficient sets to mix the second digital data stream with the first compressed digital data stream. 54. A method as defined in claim 52 wherein each of the plurality of original transform coefficient sets comprises one or more modified discrete cosine transform coefficients.