Analysis filterbank, synthesis filterbank, encoder, de-coder, mixer and conferencing system

• US 8,036,903 B2
• Filed: 05/04/2007
• Issued: 10/11/2011
• Est. Priority Date: 10/18/2006
• Status: Expired

• Current Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Original Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Inventors: Schuller, Gerald, Geiger, Ralf, Grill, Bernhard, Schnell, Markus
• Primary Examiner(s): ALBERTALLI, BRIAN LOUIS
• Application Number:
  US11/744,641
• Publication Number:
  US 20080097764A1
• Time in Patent Office: 1,621 Days
• Field of Search: None
• US Class Current: 704/500
• CPC Class Codes: G10L 19/0212 using orthogonal transformation
• CPC Class Codes: G10L 19/022 Blocking, i.e. grouping of samples in time; Choice of analysis windows; Overlap factoring
• CPC Class Codes: G10L 19/135 Vector sum excited linear prediction [VSELP]

Abstract

An embodiment of an analysis filterbank for filtering a plurality of time domain input frames, wherein an input frame comprises a number of ordered input samples, comprises a windower configured to generate a plurality of windowed frames, wherein a windowed frame comprises a plurality of windowed samples, wherein the windower is configured to process the plurality of input frames in an overlapping manner using a sample advance value, wherein the sample advance value is less than the number of ordered input samples of an input frame divided by two, and a time/frequency converter configured to provide an output frame comprising a number of output values, wherein an output frame is a spectral representation of a windowed frame.

Claims

1. Analysis filterbank for filtering a plurality of time-domain input frames of an audio signal, an input frame comprising a number of ordered input samples, comprising:

a windower configured to generate a plurality of windowed frames, a windowed frame comprising a plurality of windowed samples, wherein the windower is configured to process the plurality of input frames in an overlapping manner using a sample advance value,

wherein the sample advance value is less than the number of ordered input samples of an input frame divided by 2; and

a time/frequency converter configured to provide an output frame comprising a number of output values, an output frame being a spectral representation of a windowed frame, wherein the windower or the time/frequency converter comprises a hardware implementation.

2. Analysis filterbank according to claim 1, wherein the windower is configured to consecutively generate two windowed frames based on two input frames, which comprise more than half the number of the same ordered input samples.

3. Analysis filterbank according to claim 2, wherein the windower is configured to generate the plurality of windowed frames such that the same ordered input samples of the two input frames, on which the two consecutively generated windowed frames are based, are shifted with respect to the order of the input samples of the input frame by the sample advance value.

4. Analysis filterbank according to claim 1, wherein the windower is configured to disregard at least a latest input sample according to the order of the ordered input samples or to setting at least a latest windowed sample corresponding to the order of input samples to a predetermined value or to at least a value in a predetermined range.

5. Analysis filterbank according to claim 4, wherein the windower is configured to generate the plurality of windowed frames such that a later input frame of the two input frames with respect to time, on which the two consecutively generated windowed frames are based, comprise at least one fresh input sample as the latest input sample and with respect to time the same input samples of the earlier input frame of the two input frames earlier with respect to the order of the input samples.

6. Analysis filter bank according to claim 1, wherein the windower is configured to disregard or set a plurality of input samples to the predetermined value or to at least a value in the predetermined range, wherein the plurality of input samples comprises a connected subset of input samples comprising the latest input sample according to the order of the ordered input samples.

7. Analysis filterbank according to claim 1, wherein the windower is configured to generate a windowed frame based on an input frame and a weighing function by weighing at least an input sample based on the weighing function.

8. Analysis filterbank according to claim 1, wherein the windower is configured to generate a windowed frame based on an input frame by weighing at least a plurality of input samples of the input frame with a window function.

9. Analysis filterbank according to claim 8, wherein the windower is configured such that weighing the input frame comprises multiplying at least a plurality of input samples of the input frame with an input sample-specific windowing coefficient of the window function.

10. Analysis filterbank according to claim 8, wherein the windower is configured such that weighing the input frame comprises multiplying each input sample of the input frame with an input sample-specific windowing coefficient of the window function.

11. Analysis filterbank according to claim 1, wherein the windower is configured to generate a windowed sample z_i,n based on an expression z_i,n=w(N−

1−

n)·

x′

_i,n,

wherein i is an integer indicating a frame index or a block index of a windowed frame and/or of an input frame, wherein n=−

N, . . . , N−

1 is an integer indicating a sample index, wherein N is an integer indicating twice the number of the output values of an output frame, wherein w(N−

1−

n) is the window function and wherein x′

_i,n is an input sample with a sample index n and the frame index i.

12. Analysis filterbank according to claim 1, wherein the windower is configured to generate a windowed sample z_i,n based on an expression

z_i,n=w(N−

1−

n)·

x′

_i,n,

wherein i is an integer indicating a frame index or a block index of a windowed frame and/or of an input frame, wherein n=−

N, . . . , 7N/8−

1 is an integer indicating a sample index, wherein N is an integer indicating twice the number of the output values of an output frame, wherein w(N−

1−

n) is the window function and wherein x′

_i,n is an input sample with a sample index n and the frame index i.

13. Analysis filterbank according to claim 11, wherein the windower is configured such that N is equal to 960 and the window coefficients w(0) to w(2N−

1) obey the relations given in table 1 in the annex.

14. Analysis filterbank according to claim 13, wherein the windower is configured such that the window coefficients w(0) to w(2N−

1) comprise the values given in table 2 in the annex.

15. Analysis filterbank according to claim 11, wherein the windower is configured such that N is equal to 1024 and the window coefficients w(0) to w(2N−

1) obey the relations given in table 3 in the annex.

16. Analysis filterbank according to claim 15, wherein the windower is configured such that the window coefficients w(0) to w(2N−

1) comprise the values as given in table 4 in the annex.

17. Analysis filterbank according to claim 8, wherein the windower is configured such that the window function attributes real-valued window coefficients to a definition set.

18. Analysis filterbank according to claim 17, wherein the windower is configured such that the definition set comprises at least a number of elements being greater than or equal to the difference between the number of the ordered input samples of an input frame and the number of input samples to be disregarded or the number of windowed samples of a windowed frame set to the predetermined value or set to at least a value in the predetermined range by the windower or greater than or equal to the number of ordered input samples.

19. Analysis filterbank according to claim 8, wherein the windower is configured such that the window function is asymmetric over the definition set with respect to a midpoint of the definition set.

20. Analysis filterbank according to claim 19, wherein the windower is configured such that the window function comprises more window coefficients with an absolute value of more than 10% of a maximum absolute value of the window coefficients of the window function in a first half of the definition set than in a second half of the definition set with respect to the midpoint of the definition set, wherein the first half corresponds to the latest half of the input samples.

21. Analysis filterbank according to claim 1, wherein the sample advance value is greater than twice the number of output values of an output frame.

22. Analysis filterbank according to claim 1, wherein the windower is configured such that the predetermined value is 0.

23. Analysis filterbank according to claim 1, wherein the windower is configured to set a windowed sample to a value in the predetermined range by setting the corresponding windowed sample to a value comprising an absolute value less than a minimum threshold and/or to a value comprising an absolute value more than a maximum threshold.

24. Analysis filterbank according to claim 23, wherein the minimum threshold and/or the maximum threshold is given by 10^s or 2^s, wherein s is an integer.

25. Analysis filterbank according to claim 23, wherein the minimum threshold is determined by an absolute maximum value representable by a least significant bit or a plurality of least significant bits and/or a maximum threshold is determined by an absolute minimum value representable by a most significant bit or a plurality of most significant bits in the case of a binary representation of the input samples and/or the windowed samples.

26. Analysis filterbank according to claim 1, wherein the windower is configured such that the number of input samples disregarded, the number of windowed samples set to the predetermined value or to at least a value in the predetermined range is greater than or equal to the number of output values of an output frame divided by 16.

27. Analysis filterbank according to claim 1, wherein the windower is configured to disregard or setting to the predetermined value or to a value in the predetermined range 128 or 120 windowed samples.

28. Analysis filterbank according to claim 1, wherein the time/frequency converter is configured to provide output frames comprising less than half the number of output values compared to the number of input samples of an input frame.

29. Analysis filterbank according to claim 1, wherein time/frequency converter is configured to provide output frames comprising a number of output values, which is equal to a number of input samples of an input frame divided by an integer number greater than 2.

30. Analysis filterbank according to claim 1, wherein the time/frequency converter is configured to provide an output frame comprising a number of output values, which is equal to the number of input samples of an input frame divided by 4.

31. Analysis filterbank according to claim 1, wherein the time/frequency converter is based on at least one of a discrete cosine transform and a discrete sine transform.

32. Analysis filterbank according to claim 1, wherein the time/frequency converter is configured to provide output values X_i,k based on an expression

33. Analysis filterbank according to claim 32, wherein the time/frequency converter is configured such that N is equal to 960 or 1024.

34. Synthesis filterbank for filtering a plurality of input frames of an audio signal, each input frame comprising a number of ordered input values, comprising:

a frequency/time converter configured to provide a plurality of output frames, an output frame comprising a number of ordered output samples, an output frame being a time representation of an input frame;

a windower configured to generate a plurality of windowed frames, a windowed frame comprising a plurality of windowed samples; and

wherein the windower is configured to provide the plurality of windowed samples for a processing in an overlapping manner based on a sample advance value;

an overlap/adder configured to provide an added frame comprising a start section and a remainder section, an added frame comprising a plurality of added samples by adding at least three windowed samples from at least three windowed frames for an added sample in the remainder section of an added frame and by adding at least two windowed samples from at least two different windowed frames for an added sample in the start section,

wherein the number of windowed samples added to obtain an added sample in the remainder section is at least one sample higher compared to the number of windowed samples added to obtain an added sample in the start section, or

wherein the windower is configured to disregard at least the earliest output value according to the order of the ordered output samples or to setting the corresponding windowed samples to a predetermined value or to at least a value in a predetermined range for each windowed frame of the plurality of windowed frames; and

wherein the overlap/adder is configured to provide the added sample in the remainder section of an added frame based on at least three windowed samples from at least three different windowed frames and an added sample in the start section based on at least two windowed samples from at least two different windowed frames, wherein the frequency/time converter, the windower, or the overlap/adder comprises a hardware implementation.

35. Synthesis filterbank according to claim 34, wherein the overlap/adder is configured such that an added sample in the remainder section of an added frame corresponds to output samples which are not disregarded, windowed samples set to the predetermined value or set to a value in the predetermined range by the windower, and wherein an added sample in the start section of an added frame corresponds to an output sample which is disregarded or to a windowed sample set to the predetermined value or set to a value in the predetermined range by the windower.

36. Synthesis filterbank according to claim 34, wherein the frequency/time converter is configured to provide output frames comprising more than twice the number of output samples compared to the number of input values of an input frame.

37. Synthesis filterbank according to claim 34, wherein the frequency/time converter is configured to provide output frames comprising a number of output samples, which is equal to a number of input values of an input frame multiplied by an integer number greater than 2.

38. Synthesis filterbank according to claim 34, wherein the frequency/time converter is configured to provide an output frame comprising a number of output samples, which is equal to the number of input values of an input frame multiplied by 4.

39. Synthesis filterbank according to claim 34, wherein the frequency/time converter is based on at least one of a discrete cosine transform and a discrete sine transform.

40. Synthesis filterbank according to claim 34, wherein the frequency/time converter is configured to provide output samples x_i,n based on an expression

41. Synthesis filterbank according to claim 40, wherein the frequency/time converter is configured such that N is equal to 960 or 1024.

42. Synthesis filterbank according to claim 34, wherein the windower is configured to disregard a plurality of output samples of an output frame or setting a plurality of windowed samples to the predetermined value or to at least a value in the predetermined range.

43. Synthesis filterbank according to claim 42, wherein the windower is configured such that plurality of disregarded output samples comprises a connected subset of output samples comprising the earliest output sample according to the order of the ordered output samples, or wherein the plurality of windowed samples, which are set to the predetermined value or to at least a value in the predetermined range, comprises a connected subset of windowed samples comprising at least a windowed sample corresponding to the earliest output sample.

44. Synthesis filterbank according to claim 34, wherein the windower is configured to generate a windowed frame based on an output frame and a weighing function by weighing at least an output sample of the output frame based on the weighing function.

45. Synthesis filterbank according to claim 34, wherein the windower is configured to generate a windowed frame based on an output frame by multiplying an output sample of the output frame with a value based on a window function.

46. Synthesis filterbank according to claim 34, wherein the windower is configured to multiply at least a plurality of output samples of the output frame with an output sample-specific windowing coefficient of a window function.

47. Synthesis filterbank according to claim 46, wherein the windower is configured to multiply each output sample of the output frame with an output sample-specific windowing coefficient of the window function.

48. Synthesis filterbank according to claim 34, wherein the windower is configured to generate a windowed sample z_i,n based on an expression

z_i,n=w(n)·

x_i,n,

wherein i is an integer indicating a frame index or a block index of a windowed frame and/or of an output frame, wherein n=0, . . . , 2N−

1 is an integer indicating a sample index, wherein N is an integer indicating twice the number of the input values of an input frame and/or half the number of output sample of an output frame and/or of the windowed samples of a windowed frame, wherein w(n) is the window function and wherein x_i,n is an output sample with a sample index n and the frame index i.

49. Synthesis filterbank according to claim 34, wherein the windower is configured to generate a windowed sample z_i,n based on an expression

z_i,n=w(n)·

x_i,n,

wherein i is an integer indicating a frame index or a block index of a windowed frame and/or of an output frame, wherein n=N/8, . . . , 2N−

1 is an integer indicating a sample index, wherein N is an integer indicating twice the number of the input values of an input frame and/or half the number of output samples of an output frame and/or of the windowed samples of a windowed frame, wherein w(n) is the window function and wherein x_i,n is an output sample with a sample index n and the frame index i.

50. Synthesis filterbank according to claim 48, wherein the windower is configured such that N is equal to 960 and the window coefficients w(0) to w(2N−

1) obey the relations given in table 1 in the annex.

51. Synthesis filterbank according to claim 50, wherein the windower is configured such that the window coefficients w(0) to w(2N−

1) comprise the values given in table 2 in the annex.

52. Synthesis filterbank according to claim 48, wherein the windower is configured such that N is equal to 1024 and the window coefficients w(0) to w(2N−

1) obey the relations given in table 3 in the annex.

53. Synthesis filterbank according to claim 52, wherein the windower is configured such that the window coefficients w(0) to w(2N−

1) comprise the values given in table 4 of the annex.

54. Synthesis filterbank according to claim 45, wherein the windower is configured such that the window function attributes real-valued window coefficients to elements of a definition set.

55. Synthesis filterbank according to claim 45, wherein the windower is configured such that the window function is asymmetric over the definition set with respect to a midpoint of a definition set.

56. Synthesis filterbank according to claim 55, wherein the windower is configured such that the window function comprises more window coefficients with an absolute value of 10% of a maximum absolute value of the window coefficients of the window function in a first half of the definition set than in the second half of the definition set with respect to the midpoint of the definition set wherein the first half corresponds to the earlier half of the output values.

57. Synthesis filterbank according to claim 45, wherein the windower is configured such that the window function is based on, mirrored variant of or identical with a window function based on which the input frames are generated for the synthesis filterbank.

58. Synthesis filterbank according to claim 45, wherein the windower is configured such that the window function is a mirrored window function with respect to a midpoint of the definition set of the window function compared to a window function based on which the input frames are generated for the synthesis filterbank.

59. Synthesis filterbank according to claim 34, wherein the windower is configured such that the predetermined value is 0.

60. Synthesis filterbank according to claim 34, wherein the windower is configured to set a windowed sample to a value in the predetermined range by at least one of setting the corresponding windowed sample to a value comprising an absolute value less than a minimum threshold and setting the corresponding windowed sample to a value comprising an absolute value more than a maximum threshold.

61. Synthesis filterbank according to claim 60, wherein the minimum threshold or the maximum threshold is given by 10^s or 2^s, wherein s is an integer.

62. Synthesis filterbank according to claim 60, wherein the minimum threshold is determined by a maximum absolute value representable by a least significant bit or a plurality of a least significant bits or the maximum threshold is determined by a minimum absolute value representable by a most significant bit or a plurality of most significant bits in the case of a binary representation of at least one of the input values, the output samples and the windowed samples.

63. Synthesis filterbank according to claim 34, wherein the windower is configured such that the number of output samples disregarded or the number of windowed samples set to the predetermined value or to at least a value in the predetermined range is greater than or equal to the number of output samples of an output frame divided by 64.

64. Synthesis filterbank according to claim 34, wherein the windower is configured such that the number of output values disregarded or the number of windowed samples set to the predetermined value or to at least a value in the predetermined range is greater than or equal to the number of added samples of an added frame divided by 16.

65. Synthesis filterbank according to claim 34, wherein the windower is configured to disregard 128 or 120 or setting to the predetermined value or to at least a value in the predetermined range 128 or 120 windowed samples.

66. Synthesis filterbank according to claim 34, wherein the overlap/adder is configured to generate the added frame based on at least three consecutively generated windowed frames by the windower.

67. Synthesis filterbank according to claim 34, wherein the overlap/adder is configured to generate the added frame based on at least three consecutively generated output frames by the frequency/time converter.

68. Synthesis filterbank according to claim 34, wherein the overlap/adder is configured to generate the added frame comprising a number of added samples which is equal to the sample advance value.

69. Synthesis filterbank according to claim 34, wherein the overlap/adder is configured to provide an added frame comprising a plurality of added samples based on at least 4 windowed samples from at least 4 different windowed frames for an added sample corresponding to a windowed sample, which is not based on a disregarded output sample, set to the predetermined value and to a value in the predetermined range by the windower, and based on at least 3 windowed samples from at least 3 different windowed frames for an added sample corresponding to an output sample which is disregarded or set to the predetermined value or to a value in the predetermined range by the windower.

70. Synthesis filterbank according to claim 34, wherein the overlap/adder is configured to provide added frames comprising a number of added samples, which is less than the number of output values of an output frame divided by 2.

71. Synthesis filterbank according to claim 34, wherein the overlap/adder is configured to provide added frames comprising a number of added samples, which is equal to the number of output samples of an output frame divided by an integer larger than 2.

72. Synthesis filterbank according to claim 34, wherein the overlap/adder is configured to provide added frames comprising a number of added samples, which is equal to the number of output samples of an output frame divided by 4.

73. Synthesis filterbank according to claim 34, wherein the overlap/adder is configured to provide an added sample out_i,n based on an expression

74. Synthesis filterbank for filtering a plurality of input frames of an audio signal, each input frame comprising M ordered input values y_k(0), . . . , y_k(M−

1), wherein M is a positive integer, and wherein k is an integer indicating a frame index,

comprising;

an inverse type-IV discrete cosine transform frequency/time converter configured to provide a plurality of output frames, an output frame comprising 2M ordered output samples x_k(0), . . . , x_k(2M−

1) based on the input values y_k(0), . . . , y_k(M−

1);

a windower configured to generate a plurality of windowed frames, a windowed frame comprising a plurality of windowed samples z_k(0), . . . , z_k(2M−

1) based on the equation

z_k(n)=w(n)·

x_k(n)

for n=0, . . . , 2M−

1,

wherein n is an integer indicating a sample index, and wherein w(n) is a real-valued window function coefficient corresponding to the sample index n;

an overlap/adder configured to provide an intermediate frame comprising a plurality of intermediate samples m_k(0), . . . , m_k(M−

1) based on the equation

m_k(n)=z_k(n)+z_k-1(n+M)

for n=0, . . . , M−

1;

and

a lifter configured to provide an added frame comprising a plurality of added samples out_k(0), . . . , out_k(M−

1) based on the equation

out_k(n)=m_k(n)+l(n−

M/2)·

m_k-1(M−

1−

n)

for n=M/2, . . . , M−

1

and

out_k(n)=m_k(n)+l(M−

1−

n)·

out_k-1(M−

1−

n)

for n=0, . . . , M/2−

1,

wherein l(0), . . . , l(M−

1) are real-valued lifting coefficients, wherein inverse type-IV discrete cosine transform frequency/time converter, the windower, the overlap/adder, or the lifter comprises a hardware implementation.

75. Synthesis filterbank according to claim 74, wherein the windower is configured such that M is equal to 512 and the window coefficients w(0), . . . , w(2M−

1) obey the relations given in table 5 in the annex, and wherein the lifter is configured such that the lifting coefficients l(0), . . . , l(M−

1) obey the relations given in table 6 in the annex.

76. Synthesis filterbank according to claim 75, wherein the windower is configured such the window coefficients w(0), . . . , w(2M−

1) comprise the values given in table 7 of the annex, and wherein the lifter is configured such that the lifting coefficients l(0), . . . , l(2M−

1) comprise the values given in table 8.

77. Synthesis filterbank according to claim 74, wherein the windower is configured such that M is equal to 480 and the window coefficients w(0), . . . , w(2M−

1) obey the relations given in table 9 in the annex, and wherein the lifter is configured such that the lifting coefficients l(0), . . . , l(M−

1) obey the relations given in table 10 in the annex.

78. Synthesis filterbank according to claim 77, wherein the windower is configured such the window coefficients w(0), . . . , w(2M−

1) comprise the values given in table 11 of the annex, and where in the lifter is configured such that the lifting coefficients l(0), . . . , l(2M−

1) comprise the values given in table 12.

79. Encoder comprising:

an analysis filterbank for filtering a plurality of time-domain input frames, an input frame comprising a number of ordered input samples,

comprising;

a windower configured to generate a plurality of windowed frames, a windowed frame comprising a plurality of windowed samples, wherein the windower is configured to process the plurality of input frames in an overlapping manner using a sample advance value,

wherein the sample advance value is less than the number of ordered input samples of an input frame divided by 2; and

a time/frequency converter configured to provide an output frame comprising a number of output values, an output frame being a spectral representation of a windowed frame, wherein the windower or the time/frequency converter comprises a hardware implementation.

80. Encoder according to claim 79, further comprising an entropy encoder, configured to encode the plurality of output frames provided by the analysis filterbank and configured to output a plurality of encoded frames based on the output frames.

81. Audio decoder comprising:

a synthesis filterbank for filtering a plurality of input frames, each input frame comprising a number of ordered input values,

comprising;

a frequency/time converter configured to provide a plurality of output frames, an output frame comprising a number of ordered output samples, an output frame being a time representation of an input frame;

a windower configured to generate a plurality of windowed frames, a windowed frame comprising a plurality of windowed samples; and

wherein the windower is configured to provide the plurality of windowed samples for a processing in an overlapping manner based on a sample advance value;

an overlap/adder configured to provide an added frame comprising a start section and a remainder section, an added frame comprising a plurality of added samples by adding at least three windowed samples from at least three windowed frames for an added sample in the remainder section of an added frame and by adding at least two windowed samples from at least two different windowed frames for an added sample in the start section,

wherein the number of windowed samples added to obtain an added sample in the remainder section is at least one sample higher compared to the number of windowed samples added to obtain an added sample in the start section, or

wherein the windower is configured to disregard at least the earliest output value according to the order of the ordered output samples or to setting the corresponding windowed samples to a predetermined value or to at least a value in a predetermined range for each windowed frame of the plurality of windowed frames; and

wherein the overlap/adder is configured to provide the added sample in the remainder section of an added frame based on at least three windowed samples from at least three different windowed frames and an added sample in the start section based on at least two windowed samples from at least two different windowed frames, wherein the frequency/time converter, the windower, or the overlap/adder comprises a hardware implementation.

82. Audio decoder according to claim 81, further comprising an entropy decoder configured to decode a plurality of encoded frames and configured to provide a plurality of input frames based on the encoded frames to the synthesis filterbank.

83. Audio decoder comprising:

a synthesis filterbank for filtering a plurality of input frames, each input frame comprising M ordered input values y_k(0), . . . , y_k(M−

1), wherein M is a positive integer, and wherein k is an integer indicating a frame index, comprising;

an inverse type-IV discrete cosine transform frequency/time converter configured to provide a plurality of output frames, an output frame comprising 2M ordered output samples x_k(0), . . . , x_k(2M−

1) based on the input values y_k(0), . . . , y_k(M−

1);

a windower configured to generate a plurality of windowed frames, a windowed frame comprising a plurality of windowed samples z_k(0), . . . , z_k(2M−

1) based on the equation

z_k(n)=w(n)·

x_k(n)

for n=0, . . . , 2M−

1,

wherein n is an integer indicating a sample index, and wherein w(n) is a real-valued window function coefficient corresponding to the sample index n;

an overlap/adder configured to provide an intermediate frame comprising a plurality of intermediate samples m_k(0), . . . , m_k(M−

1) based on the equation

m_k(n)=z_k(n)+z_k-1(n+M)

for n=0, . . . , M−

1;

and

a lifter configured to provide an added frame comprising a plurality of added samples out_k(0), . . . , out_k(M−

1) based on the equation

out_k(n)=m_k(n)+l(n−

M/2)·

m_k-1(M−

1−

n)

for n=M/2, . . . , M−

1

and

out_k(n)=m_k(n)+l(M−

1−

n)·

out_k-1(M−

1−

n)

for n=0, . . . , M/2−

1,

wherein l(0), . . . , l(M−

1) are real-valued lifting coefficients, wherein inverse type-IV discrete cosine transform frequency/time converter, the windower, the overlap/adder, or the lifter comprises a hardware implementation.

84. Audio decoder according to claim 83, further comprising an entropy decoder configured to decode a plurality of encoded frames and configured to provide a plurality of input frames based on the encoded frames to the synthesis filterbank.

85. Mixer for mixing a plurality of input frames, each input frame being a spectral representation of a corresponding time-domain frame and each input frame of the plurality of input frames being provided from a different audio source, comprising:

an entropy decoder configured to entropy decode the plurality of input frames;

a scaler configured to scale the plurality of entropy decoded input frames in the frequency domain and configured to obtain a plurality of scaled frames in the frequency domain, each scaled frame corresponding to an entropy decoded input frame;

an adder configured to add up the scaled frames in the frequency domain to generate an added frame in the frequency domain; and

an entropy encoder configured to entropy encoding the added frame to obtain a mixed frame, wherein the entropy decoder, the scaler, the adder, or the entropy encoder comprises a hardware implementation.

86. Mixer according to claim 85, further comprising a dequantizer configured to dequantize the entropy decoded input frames and to provide the entropy decoded input frames to the scaler in a dequantized form.

87. Mixer according to claim 85, further comprising a quantizer configured to quantize the added frame and to provide the added frame in a quantized form to the entropy encoder.

88. Mixer according to claim 85, wherein the scaler is configured to scale the dequantized input frames by multiplying each input value of the plurality of input frames by 1/P, wherein P is an integer indicating a number of different sources.

89. Mixer according to claim 85, wherein the scaler is configured to scale the entropy decoded input frames by scaling the input values of the input frames in an energy-conserving manner.

90. Mixer according to claim 85, wherein the mixer is configured to provide the mixed frame based on the plurality of input frames, wherein each input frame of the plurality of input frames is generated based on the same synthesis window function.

91. Mixer according to claim 85, wherein the mixer is configured to generate the mixed frame based on the plurality of input frames, wherein each of the input frames of the plurality of input frames is generated by an encoder comprising an analysis filterbank for filtering a plurality of time-domain input frames, an input frame comprising a number of ordered input samples, comprising a windower configured to generate a plurality of windowed frames, a windowed frame comprising a plurality of windowed samples, wherein the windower is configured to process the plurality of input frames in an overlapping manner using a sample advance value, wherein the sample advance value is less than the number of ordered input samples of an input frame divided by 2;

and a time/frequency converter configured to provide an output frame comprising a number of output values, an output frame being a spectral representation of a windowed frame.

92. Mixer according to claim 85, wherein the mixer is configured to process the plurality of input frames and to provide the mixed frame based corresponding to a bitrate of less than 36 kbit/s per channel.

93. Conferencing system comprising:

a mixer for mixing a plurality of input frames, each input frame being a spectral representation of a corresponding time-domain frame and each input frame of the plurality of input frames being provided from an audio different source,

comprising;

an entropy decoder configured to entropy decode the plurality of input frames;

a scaler configured to scale the plurality of entropy decoded input frames in the frequency domain and configured to obtain a plurality of scaled frames in the frequency domain, each scaled frame corresponding to an entropy decoded input frame;

an adder configured to add up the scaled frames in the frequency domain to generate an added frame in the frequency domain; and

an entropy encoder configured to entropy encoding the added frame to obtain a mixed frame, wherein the entropy decoder, the scaler, the adder, or the entropy encoder comprises a hardware implementation.

94. Method for filtering a plurality of time domain input frames of an audio signal, an input frame comprising a number of ordered input samples,

the method comprising:

generating, performed by a windower, a plurality of windowed frames by processing the plurality of input frames in an overlapping manner using a sample advance value;

wherein the sample advance value is less than the number of ordered input samples of an input frame divided by 2; and

providing, performed by a time/frequency converter, a plurality of output frames comprising a number of output values by performing a time/frequency conversion, an output frame being a spectral representation of a windowed frame, wherein the windower or the time/frequency converter comprises a hardware implementation.

95. Method for filtering a plurality of input frames of an audio signal, each input frame comprising a number of ordered input values,

the method comprising:

performing, performed by a frequency/time converter, a frequency/time conversion and providing a plurality of output frames, an output frame comprising a number of ordered output samples, an output frame being a time representation of an input frame;

generating, performed by a windower, a plurality of windowed frames, a windowed frame comprising a plurality of windowed samples by processing the plurality of output samples for processing the windowed frames in an overlapping manner based on a sample advanced value;

generating, performed by an overlap/adder, an added frame comprising a start section and a remainder section,

wherein a added frame comprises an added sample by adding at least three windowed samples from at least three different windowed frames for an added sample in the remainder section of an added frame and an added sample by adding at least two windowed samples from at least two different windowed frames for an added sample in the start section,

wherein the number of windowed samples added to obtain an added sample is in the remainder section at least one sample higher compared to the number of windowed samples added to obtain an added sample in the start section;

or

wherein generating the plurality of windowed frames comprises disregarding at least the earliest output sample according to the order of the ordered output sample or to setting the corresponding windowed sample to a predetermined value to at least a value in a predetermined range for each windowed frame of the plurality of windowed frames; and

wherein providing an added frame comprises providing an added sample by adding at least three windowed samples from at least three different windowed frames for an added sample in the remainder section of an added frame and an added sample by adding at least two windowed samples from at least two different windowed frames for an added sample in the start section, wherein the frequency/time converter, the windower, or the overlap/adder comprises a hardware implementation.

96. Method for filtering a plurality of input frames of an audio signal, each input frame comprising M ordered input values y_k(0), . . . , y_k(M−

1), wherein M is a positive integer, and wherein k is an integer indicating an index of the input frame,

the method comprising;

performing, performed by an inverse type-IV discrete cosine transform/time converter, an inverse type-IV discrete cosine transform and providing a plurality of output frames x_k(0), . . . , x_k(2M−

1) based on the input values y_k(0), . . . , y_k(M−

1);

generating, performed by a windower, a plurality of windowed frames, a windowed frame comprising a plurality of windowed samples z_k(0), . . . , z_k(2M−

1) based on an equation

z_k(n)=w(n)·

x_k(n)

for n=0, . . . , 2M−

1,

wherein n is an integer;

generating, performed by an overlap/adder, a plurality of intermediate frames, each intermediate frame comprising a plurality of intermediate samples mk(0), . . . , mk(M−

1) based on the equation

m_k(n)=z_k(n)+z_k-1(n+M)

for n=0, . . . , M−

1;

and

generating, performed by a lifter, a plurality of added frames comprising a plurality of added samples out_k(0), . . . , out_k(M) based on an equation

out_k(n)=m_k(n)+l(n−

M/2)·

m_k-1(M−

1−

n)

for n=M/2, . . . , M−

1

and

out_k(n)=m_k(n)+l(M−

1−

n)·

out_k-1(M−

1−

n)

for n=0, . . . , M/2−

1,

wherein w(0), . . . , w(2M−

1) are real-valued window coefficients;

wherein l(0), . . . , l(M−

1) are real-valued lifting coefficients; and

wherein inverse type-IV discrete cosine transform frequency/time converter, the windower, the overlap/adder, or the lifter comprises a hardware implementation.

97. Non-transitory computer-readable medium having stored thereon a computer program for performing, when running on a computer, a method for filtering a plurality of time domain input frames of an audio signal, an input frame comprising a number of ordered input samples,

comprising:

generating a plurality of windowed frames by processing the plurality of input frames in an overlapping manner using a sample advance value;

wherein the sample advance value is less than the number of ordered input samples of an input frame divided by 2; and

providing a plurality of output frames comprising a number of output values by performing a time/frequency conversion, an output frame being a spectral representation of a windowed frame.

98. Non-transitory computer-readable medium having stored thereon a computer program for performing, when running on a computer, a method for filtering a plurality of input frames of an audio signal, each input frame comprising a number of ordered input values, comprising:

performing a frequency/time conversion and providing a plurality of output frames, an output frame comprising a number of ordered output samples, an output frame being a time representation of an input frame;

generating a plurality of windowed frames, a windowed frame comprising a plurality of windowed samples by processing the plurality of output samples for processing the windowed frames in an overlapping manner based on a sample advanced value;

generating an added frame comprising a start section and a remainder section,

wherein a added frame comprises an added sample by adding at least three windowed samples from at least three different windowed frames for an added sample in the remainder section of an added frame and an added sample by adding at least two windowed samples from at least two different windowed frames for an added sample in the start section,

wherein the number of windowed samples added to obtain an added sample is in the remainder section at least one sample higher compared to the number of windowed samples added to obtain an added sample in the start section;

or

wherein generating the plurality of windowed frames comprises disregarding at least the earliest output sample according to the order of the ordered output sample or to setting the corresponding windowed sample to a predetermined value to at least a value in a predetermined range for each windowed frame of the plurality of windowed frames; and

wherein providing an added frame comprises providing an added sample by adding at least three windowed samples from at least three different windowed frames for an added sample in the remainder section of an added frame and an added sample by adding at least two windowed samples from at least two different windowed frames for an added sample in the start section.

99. Non-transitory computer-readable medium having stored thereon a computer program for performing, when running on a computer, a method for filtering a plurality of input frames of an audio signal, each input frame comprising M ordered input values y_k(0), . . . , y_k(M−

1), wherein M is a positive integer, and wherein k is an integer indicating an index of the input frame,

comprising;

performing an inverse type-IV discrete cosine transform and providing a plurality of output frames x_k(0), . . . , x_k(2M−

1) based on the input values y_k(0), . . . , y_k(M−

1);

generating a plurality of windowed frames, a windowed frame comprising a plurality of windowed samples z_k(0), . . . , z_k(2M−

1) based on an equation

z_k(n)=w(n)·

x_k(n)

for n=0, . . . , 2M−

1,

wherein n is an integer;

generating a plurality of intermediate frames, each intermediate frame comprising a plurality of intermediate samples m_k(0), . . . , m_k(M−

1) based on the equation

m_k(n)=z_k(n)+z_k-1(n+M)

for n=0, . . . , M−

1;

and

generating a plurality of added frames comprising a plurality of added samples out_k(0), . . . , out_k(M) based on an equation

out_k(n)=m_k(n)+l(n−

M/2)·

m_k-1(M−

1−

n)

for n=M/2, . . . , M−

1

and

out_k(n)=m_k(n)+l(M−

1−

n)·

out_k-1(M−

1−

n)

for n=0, . . . , M/2−

1,

wherein w(0), . . . , w(2M−

1) are real-valued window coefficients; and

wherein l(0), . . . , l(M−

1) are real-valued lifting coefficients.