Claims
1. Audio post-processor (100) for post-processing an audio signal (102) having a
time-variable high frequency gain information (104) as side information (106),
comprising:
a band extractor (110) for extracting a high frequency band (112) of the audio signal (102) and a low frequency band (114) of the audio signal (102);
a high band processor (120) for performing a time-variable amplification of the high frequency band (112) in accordance with the time-variable high frequency gain information (104) to obtain a processed high frequency band (122);
a combiner (130) for combining the processed high frequency band (122) and the low frequency band (114).
2. Audio post-processor of claim 1, in which the band extractor (110) is configured to extract the low frequency band using a low pass filter device (111) and to extract the high frequency band by subtracting (113) the low frequency band from the audio signal.
3. Audio post-processor of claim 1 or 2, in which the time-variable high frequency gain information (104) is provided for a sequence (300-303) of blocks of sampling values of the audio signal (102) so that a first block (301) of sampling values has associated therewith a first gain information (311) and a second later block (302) of sampling values of the audio signal has a different second gain information (312), wherein the band extractor (110) is configured to extract, from the first block (301) of sampling values, a first low frequency band and a first high frequency band and to extract, from the second block (302) of sampling values, a second low frequency band and a second high frequency band, and
wherein the high band processor (120) is configured to modify the first high frequency band using the first gain information (311) to obtain a first processed high frequency band and to modify the second high frequency band using the second gain information (312) to obtain a second processed high frequency band, and

wherein the combiner (130) is configured to combine the first low frequency band and the first processed high frequency band to obtain a first combined block and to combine the second low frequency band and the second processed high frequency band to obtain a second combined block.
4, Audio post-processor of one of the preceding claims,
wherein the band extractor (110) and the high band processor (120) and the combiner (130) are configured to operate in overlapping blocks, and
wherein the audio post-processor (100) further comprises an overlap-adder (140) for calculating a post-processed portion by adding audio samples of a first block (301) and audio samples of a second block (302) in a block overlap range.
5, Audio post-processor of one of the preceding claims, wherein the band extractor
(110) comprises:
an analysis windower (115) for generating a sequence of blocks of sampling values of the audio signal using an analysis window, wherein the blocks are time-overlapping;
a discrete Fourier transform processor (116) for generating a sequence of blocks of spectral values;
a low pass shaper (117) for shaping each block of spectral values to obtain a sequence of low pass shaped blocks of spectral values;
a discrete Fourier inverse transform processor (118) for generating a sequence of blocks of low pass time domain sampling values; and
a synthesis windower (119) for windowing the sequence of blocks of low pass time domain sampling values using a synthesis window.
6, Audio post-processor of claim 5, wherein the band extractor (110) further
comprises:

an audio signal windower (121) for windowing the audio signal (102) using the analysis window and the synthesis window to obtain a sequence of windowed blocks of audio signal values, wherein the audio signal windower (121) is synchronized with the windower (115, 119) so that the sequence of blocks of low pass time domain sampling values is synchronous with the sequence of windowed blocks of audio signal values.
7. Audio post-processor of claim 5 or 6,
wherein the band extractor (110) is configured to perform a sample-wise subtraction (113) of the sequence of blocks of low pass time domain values from a corresponding sequence of blocks derived from the audio signal to obtain a sequence of blocks of high pass time domain sampling values.
8. Audio post-processor of claim 7,
wherein the high band processor (120) is configured to apply the modification to each sample of each block of the sequence of blocks of high pass time domain sampling values,
wherein the modification for a sample of a block depends on
a gain information of a previous block and a gain information of the current block, or
a gain information of the current block and a gain information of the next block.
9. Audio post-processor of one of the claims 1 to 7, wherein the audio signal
comprises an additional control parameter (500) as a further side information,
wherein the high band processor (120) is configured to apply the modification also
under consideration of the additional control parameter (500), wherein a time
resolution of the additional control parameter (500) is lower than a time resolution
of the time-varying high frequency gain information or the additional control
parameter is stationary for a specific audio piece.

10. Audio post-processor of claim 8,
wherein the combiner (130) is configured to perform a sample-wise addition of corresponding blocks of the sequence of blocks of low pass time domain sampling values and the sequence of amplified blocks of high pass time domain sampling values to obtain a sequence of blocks of combination signal values,
11. Audio post-processor of claim 10, further comprising;
an overlap-add (140) processor for calculating a post-processed audio signal portion by adding audio samples of a first block (301) of the sequence of combination signal values and audio samples of a neighboring second block (302) adjacent to the first block in a block overlap range (321).
12. Audio post-processor of one of the preceding claims,
wherein the band extractor (110), the high band processor (120) and the combiner (130) operate in overlapping blocks, wherein an overlap range (321) is between 40% of a block length and 60% of a block length, or
wherein a block length is between 0.8 milliseconds and 5 milliseconds, or
wherein the modification performed by the high band processor (120) is an multiplicative factor applied to each sample of a block in a time domain, or
wherein a cutoff or corner frequency of the low frequency band is between 1/8 and 1/3 of a maximum frequency of the audio signal and preferably equal to 1/6 of the maximum frequency of the audio signal.
13. Audio post-processor of claim 5,
wherein the low pass shaper (117) is configured to apply a shaping function depending on the time-variable high frequency gain information (104) for a corresponding block.

14. Audio post-processor of claim 13,
wherein the shaping function additionally depends on a shaping function used in an audio pre-processor (200) for modifying or attenuating a high frequency band of the audio signal using the time-variable high frequency gain information for a corresponding block.
15. Audio post-processor of claim 8,
wherein the modification for a sample of a block additionally depends on a windowing factor applied for a certain sample as defined by the analysis window function or the synthesis window function.
16. Audio post-processor of one of the preceding claims, wherein the band extractor (110), the high band processor (120) and the combiner (130) are configured to process sequences of blocks (300-303) derived from the audio signal as overlapping blocks, so that a later portion of an earlier block is derived from the same audio samples of the audio signal as an earlier portion of a later block being adjacent in time to the earlier block.
17. Audio post-processor of claim 16, wherein an overlap range (321) of the overlapping blocks is equal to one half of the earlier block and wherein the later block has the same length as the earlier block with respect to a number of sample values, and wherein the post processor additionally comprises an overlap adder (140) for performing the overlap add operation.
18. Audio post-processor of claim 16 or 17, wherein the band extractor (110) is configured to apply a slope of a splitting filter (111) between a stop range and a pass range of the splitting filter to a block of audio samples, wherein the slope depends on the time-variable high frequency gain information for the block of samples.
19. Audio post-processor of claim 18,

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wherein the high frequency gain information comprises gain values, wherein the slope is increased stronger for a higher gain value compared to an increase of the slope for a lower gain value.
20. Audio post-processor of one of claims 17 to 19,
wherein the slope of the splitting filter (111) is defined based on the following equation:
g[k] rslf] = 1 - (1 - PS[/J) x T-1M-W-U——
wherein rs[f] is the slope of the splitting filter (111), wherein ps[f] is a slope of splitting filter used when generating the audio signal, wherein g[k] is a gain factor derived from the time-variable high frequency gain information, wherein f is a frequency index and wherein k is a block index.
21. Audio post-processor of any one of the claims 16 to 20,
wherein the high frequency gain information comprises gain values for adjacent blocks, wherein the high band processor (120) is configured to calculate a correction factor for each sample depending on the gain values for the adjacent blocks and depending on window factors for corresponding samples.
22. Audio post-processor of claim 21, wherein the high band processor (120) is
configured to operate based on the following equations:
fg[k-l] g[k] \ , N
corr[/] = 1 + ^-^1+^^-2] x w2\j] x (1 - w2[/]),for 0 <; < -.
corrfi + "] = l + f4^ + ^^-2)xw2[/]x(l-w2[/l),for0 j 2
wherein corrQ] is a correction factor for a sample with an index j, wherein g[k-1] is a gain factor for a preceding block, wherein g[k] is a gain factor a current block, wherein wQ] is a window function factor for a sample with a sample index j, wherein N is the length in samples of a block and wherein g[k+1] is the gain factor for the

later block, wherein k is the block index and wherein the upper equation from the above equations is for a first half of an output block k, and wherein the lower equation of the above equations is for a second half of the output block k.
23. Audio post-processor of one of claims 17 to 22,
wherein the high band processor (120) is configured to additionally compensate for an attenuation of transient events introduced into the audio signal by a processing performed before a processing by the audio post-processor (100).
24. Audio post-processor of claim 23,
wherein the high band processor is configured to operate based on the following equation:
gc[k] = (1 + betajactor) x g[k] — beta_factor
wherein gc[k] is the compensated gain for a block with a block index k, wherein g[k] is a non-compensated gain as indicated by the time-variable high frequency
gain information included as the side information and wherein betajactor (500) is an additional control parameter value included within the side information (106).
25. Audio post-processor of one of claims 22 and 24, wherein the high band processor
(120) is configured to calculate the processed high band based on the following
equation:
phpb[/c][i] = —FTTX F^xhpb[/c][i],for0 Tailiet
hp_e[fc] F~ quiet,
1, otherwise
wherein gf|0at is a non-quantized gain factor, wherein k is a block index, wherein a is a variation influencing factor, wherein hp_bg__e[k] is the high frequency

background energy for a block k, wherein hp_e[k] is the energy of the high frequency block, wherein T__quiet is a quiet threshold, and wherein the factor a and the quiet threshold are predetermined or controllable by additional control parameters.
36. Audio pre-processor of one of the claims 32 to 35, wherein the signal analyzer (260) and the high band processor (120) are configured to calculate the time-variable high frequency gain information and to apply the time-variable high frequency gain information so that a variation of an energy of each block around a corresponding average energy of a background is reduced by at least 50% and preferably by 75%.
37. Audio pre-processor of one of claims 32 to 36,
wherein the signal analyzer (260) is configured to quantize and clip (812) a raw sequence of gain information values to obtain the time-variable high frequency gain information as a sequence of quantized values,
wherein the high band processor (220) is configured to perform (813) the time-variable modification of the high band in accordance with the sequence of quantized values, and
wherein the output interface (250) is configured to introduce (814) the sequence of quantized values into the side information (206) as the time-variable high frequency gain information (204).
38. Audio pre-processor of one of claims 32 to 37, wherein the audio pre-processor
(200) is configured
to determine (815) a further gain compensation value describing a loss of an energy variation introduced by a subsequently connected encoder or decoder, and
to quantize (816) the further gain compensation information, and

wherein the output interface (250) is configured to introduce (817) the quantized further gain compensation information into the side information.
39. Audio pre-processor of one of claims 32 to 38, wherein the signal analyzer (260) is
configured to apply meta gain control (806) which controls the further modification
of the calculated time-variable high frequency gain information to gradually reduce
or gradually enhance an effect of the high band processor (220) on the audio
signal in accordance with additional control data (807) additionally derived from the
audio signal, or
where in the signal analyzer (260) is configured to influence a factor alpha when calculating the gain information based on the following equation, wherein increasing alpha results in a stronger influence and reducing alpha results in a lower influence,
!
a x hp_bg„e[fc] + (1 - a) x hp„e[fc]
■ •—__— ----- ———, whenhp e[k] > Tauiet
hp_e[fc] F- qme1, otherwise
wherein gfl0at is a non-quantized gain factor, wherein k is a block index, wherein hp_bg_e[k] is the high frequency background energy for a block k, wherein hp_e[k] is the energy of the high frequency block, wherein T_quiet is a quiet threshold, and wherein the factor a and the quiet threshold are predetermined or controllable by additional control parameters.
40. Audio pre-processor of one of claims 32 to 39, in which the band extractor (210) is configured to extract the low frequency band using a low pass filter device (111) and to extract the high frequency band by subtracting (113) the low frequency band from the audio signal.
41. Audio pre-processor of one of claims 32 to 40,
in which the time-variable high frequency gain information (204) is provided for a sequence (300-303) of blocks of sampling values of the audio signal so that a first block (301) of sampling values has associated therewith a first gain information

(311) and a second later block (302) of sample values of the audio signal has a different second gain information (312), wherein the band extractor is configured to extract, from the first block of sampling values, a first low frequency band and a first high frequency band and to extract, from the second block of sampling values, a second low frequency band and a second high frequency band, and
wherein the high band processor (220) is configured to modify the first high frequency band using the first gain information (311) to obtain a first processed high frequency band and to modify the second high frequency band using the second gain information (312) to obtain a second processed high frequency band, and
wherein the combiner (230) is configured to combine the first low frequency band and the first processed high frequency band to obtain a first combined block and to combine the second low frequency band and the second processed high frequency band to obtain a second combined block.
42. Audio pre-processor in accordance with one of claims 32 to 41,
wherein the band extractor (210) and the high band processor (220) and the combiner (230) are configured to operate in overlapping blocks, and
wherein the combiner (230) further comprises an overlap-adder for calculating a post-processed portion by adding audio samples of a first block and audio samples of a second block in a block overlap range (321), or
wherein the band extractor (210), the high band processor (220) and the combiner (230) operate in overlapping blocks, wherein an overlap range (321) is between 40% of a block length and 60% of a block length, or
wherein a block length is between 0.8 milliseconds and 5 milliseconds, or
wherein the modification performed by the high band processor (220) is an attenuation applied to each sample of a block in a time domain, or

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wherein a cutoff or corner frequency of the low frequency band is between 1/8 and 1/3 of a maximum frequency of the audio signal (202) and preferably equal to 1/6 of the maximum frequency of the audio signal.
43, Audio pre-processor in accordance with one of claims 32 to 42, wherein the band
extractor (210) comprises:
an analysis windower (215) for generating a sequence of blocks of sampling values of the audio signal using an analysis window, wherein the blocks are time-overlapping;
a discrete Fourier transform processor (216) for generating a sequence of blocks of spectral values;
a low pass shaper (217a, 217b) for shaping each block of spectral values to obtain a sequence of low pass shaped blocks of spectral values;
a discrete Fourier inverse transform processor (218) for generating a sequence of blocks of low pass time domain sampling values; and
a synthesis windower (219) for windowing the sequence of blocks of low pass time domain sampling values using a synthesis window.
44. Audio pre-processor in accordance with claim 43, wherein the low pass shaper
(217a, 217b) is configured to operate based on the following equation:
r 1, for 0 < / < ip^size
/ — Ip^size + 1
rrn 1 —, for Ip size < f < In size + tr size
psL/J = \ tr_size + 1 r~ iv-
N
0, for lp„size + tr^size < / < —
v I
wherein psjTj indicates the shaping factor of the shaping to be applied by the low pass shaper for a frequency value f, wherein f is a frequency value, wherein tr_size is a value determining the width in spectral lines of a transition region, wherein a lp__size indicates a size of a low pass portion without the transition region, wherein N indicates a number of sampling values for a block.

45. Audio pre-processor of one of claims 43 or 44, wherein the block extractor further
comprises:
an audio signal windower (221) for windowing the audio signal using the analysis window and the synthesis window to obtain a sequence of windowed blocks of audio signal values, wherein the audio signal windower is synchronized with the windower (215, 219) so that the sequence of blocks of low pass time domain sampling values is synchronous with the sequence of windowed blocks of audio signal values.
46. Audio pre-processor of one of claims 43 to 45,
wherein the band extractor (210) is configured to perform a sample-wise subtraction (113) of the sequence of blocks of low pass time domain values from a corresponding sequence of blocks derived from the audio signal to obtain a sequence of blocks of high pass time domain sampling values.
47. Audio pre-processor of one of claims 32 to 46, wherein the analyzer (260) additionally provides a control parameter (807) computed by meta gain control (806), wherein the high band processor (220) is configured to apply the modification also under consideration of the control parameter.
48. Audio pre-processor of one of claims 43 to 47,
wherein the combiner (230) is configured to perform a sample-wise addition of corresponding blocks of the sequence of blocks of low pass time domain sampling values and the sequence of modified blocks of high pass time domain sampling values to obtain a sequence of blocks of combination signal values.
49. Audio pre-processor of claim 48, further comprising:
an overlap-add processor for calculating a pre-processed audio signal portion by adding audio samples of a first block of the sequence of combination signal values and audio samples of a neighboring second block adjacent to the first block in a block overlap range.

50. Audio pre-processor of one of claims 32 to 49, wherein
wherein the band extractor (211), the high band processor (720) and the combiner (230) operate in overlapping blocks, wherein an overlap range is between 40% of a block length and 60% of a block length, or
wherein a block length is between 0.8 milliseconds and 5 milliseconds, or
wherein the modification performed by the high band processor (220) is an multiplicative factor applied to each sample of a block in time domain.
51. Audio pre-processor of one of claims 32 to 50,
wherein an overlap range (321) of the overlapping blocks is equal to one half of the earlier block and wherein the later block has the same length as the earlier block with respect to a number of sample values, and wherein the combiner comprises and overlap adder for performing the overlap add operation.
52. Audio post-processor of one of claims 32 to 51,
being configured to only perform a preprocessing with a maximum number of channels or objects to generate the side information (206) for the maximum number of channels or objects and not perform any preprocessing with a number of channels or objects for which the side information (206) is not generated, or
wherein the band extractor (210) is configured to not perform any band extraction or to not compute a Discrete Fourier Transform and inverse Discrete Fourier Transform pair for trivial gain factors for the time-variable high frequency gain information (204) determined by the signal analyzer (260) and to pass through an unchanged or windowed time domain signal associated with the trivial gain factors.
53. Audio encoding apparatus for encoding an audio signal, comprising;

the audio pre-processor of any one of claims 32 to 52, configured to generate the output signal (252) having the time-variable high frequency gain information as side information;
a core encoder (900) for generating a core encoded signal (902) and core side information (904); and
an output interface (910) for generating an encoded signal (912) comprising the core encoded signal (902), the core side information (904) and the time-variable high frequency gain information as additional side information (106).
54. Audio encoding apparatus of claim 53, wherein the audio signal is a multichannel or multi-object signal, wherein the audio pre-processor (200) is configured to pre-process each channel or each object separately and wherein the core encoder (900) is configured to apply a joint multichannel encoder processing or a joint multi object encoder processing or an encoder bandgap filling or an encoder bandwidth extension processing on the pre-processed channels (232).
55. Audio decoding apparatus, comprising:
an input interface (920) for receiving an encoded audio signal (912) comprising a core encoded signal (902), core side information (904) and the time-variable high frequency gain information (104) as additional side information;
a core decoder (930) for decoding the core encoded signal (902) using the core side information (904) to obtain a decoded core signal; and
a post-processor (100) for post-processing the decoded core signal (102) using the time-variable high frequency gain information (104) in accordance with any of the claims 1 to 31.
56. Audio decoder apparatus in accordance with claim 55,
wherein the core decoder (930) is configured to apply a multichannel decoder processing or a multi object decoder processing or a bandwidth extension decoder

processing or a gap filling decoder processing for generating decoded channels of a multichannel signal (102) or decoded objects of a multi object signal (102), and
wherein the post-processor (100) is configured to apply the post-processing individually on each channel or each object using the individual time-variable high frequency gain information for each channel or each object.
57. Method of post-processing (100) an audio signal (102) having a time-variable high
frequency gain information (104) as side information (106), comprising:
extracting (110) a high frequency band (112) of the audio signal and a low frequency band (114) of the audio signal;
performing (120) a time-variable modification of the high band in accordance with the time-variable high frequency gain information (104) to obtain a processed high frequency band (122); and
combining (130) the processed high frequency band (122) and the low frequency band (114).
58. Method of pre-processing (200) an audio signal (202), comprising:
analyzing (260) the audio signal (202) to determine a time-variable high frequency gain information (204);
extracting (210) a high frequency band (212) of the audio signal and a low frequency band (214) of the audio signal;
performing (220) a time-variable modification of the high frequency band in accordance with the time-variable high frequency gain information to obtain a processed high frequency band;
combining (230) the processed high frequency band (222) and the low frequency band (214) to obtain a pre-processed audio signal; and

generating (250) an output signal (252) comprising the pre-processed audio signal (232) and the time-variable high frequency gain information (204) as side information (106).
59. Method of encoding an audio signal, comprising:
the method of audio pre-processing (200) of claim 58 configured to generate the output signal having the time-variable high frequency gain information (204) as side information (106);
generating a core encoded signal (902) and core side information (904); and
generating (910) an encoded signal (912) comprising the core encoded signal (902), the core side information (904) and the time-variable high frequency gain information (204) as additional side information (106).
60. Method of audio decoding, comprising:
receiving (920) an encoded audio signal (912) comprising a core encoded signal (902), core side information (904) and the time-variable high frequency gain information (204) as additional side information (106);
decoding (930) the core encoded signal (902) using the core side information (904) to obtain a decoded core signal (102); and
post-processing (100) the decoded sore signal (102) using the time-variable high frequency gain information (104) in accordance with the method of claim 55.
61. Computer program for performing, when running on a computer or a processor,
any one of the methods in accordance with claim 57, 58, 59, 60.