Claims

1. An audio decoder (100; 200;700) for providing a decoded audio information (112;

212; 712) on the basis of an encoded audio information (110;210;710), wherein the audio decoder is configured to obtain decoded spectral values (132;232;732; Xq[n], Xq[n+1]) on the basis of an encoded information (130; 230) representing the spectral values,

wherein the audio decoder is configured to jointly decode (950; 1110a-1110g) two or more most significant bits per spectral value on the basis of respective symbol codes (sym) for a set of spectral values using an arithmetic decoding,

wherein a respective symbol code (sym) represents two or more most significant bits per spectral value for one or more spectral values,

wherein the audio decoder is configured to decode (972; 1140a-1141j) one or more least significant bits associated with one or more of the spectral values in dependence on how much least significant bit information is available,

such that one or more least significant bits associated with one or more of the spectral values are decoded, while no least significant bits are decoded for one or more other spectral values for which one or more most significant bits are decoded and which comprise more bits than the one or more most significant bits; and

wherein the audio decoder is configured to provide the decoded audio information using the spectral values.

2. The audio decoder according to claim 1, wherein the audio decoder is configured to map (1110f, 1110g) one symbol (sym) of an arithmetically encoded representa- tion, which represents at least two most significant bits of at least one spectral val- ue, onto the at least two most significant bits of the at least one spectral value.

3. The audio decoder according to claim 1 or claim 2, wherein the arithmetic decod- ing is configured to determine (1110a-1110e) bit positions (numbits, numbits-1) of the at least two most significant bits and to allocate (1110f, 1110g) the at least two most significant bits determined by a symbol (sym) of the arithmetically encoded representation to the determined bit positions

4. The audio decoder according to one of claims 1 to 3, wherein the audio decoder is configured to decode (954; 1120a-1120e), for all spectral values for which two or more most significant bits have been decoded and which comprise more bits than the two or more most significant bits and a least significant bit, one or more inter- mediate bits, bit positions of which are between the least significant bit and the two or more most significant bits.

5. The audio decoder according to one of claims 1 to 4, wherein the audio decoder is configured to decode, in a first decoding phase,

- two or more most significant bits per spectral value (950; 1110a-1110g), and - for all spectral values for which two or more most significant bits are decoded and which comprise more bits than the two or more most significant bits and a least significant bit, one or more intermediate bits (954; 1120a-1120e), bit posi- tions of which are between the least significant bit and the two or more most significant bits, and

- for all spectral values for which two or more most significant bits are decoded and for which the two or more most significant bits and any intermediate bits, as far as intermediate bits are present, indicate a non-zero value, signs (958; 1130a-1131d); and

wherein the audio decoder is configured to selectively omit (1130a, 1131a), in the first decoding phase, a decoding of a sign for spectral values for which the two or more most significant bits and any intermediate bits, as far as intermediate bits are present, indicate a zero value, and

wherein the audio decoder is configured to selectively obtain (972; 1140h- 1140j, 1141h-1141j), in a second decoding phase which follows the first decoding phase, sign information for spectral values for which the two or more most signifi- cant values and any intermediate bits, as far as intermediate bits are present, indi- cate a zero value and for which a least significant bit information indicates a non- zero value.

6. The audio decoder according to one of claims 1 to 5, wherein the audio decoder is configured to sequentially use (1140e, 1140i, 1141e, 1141i) subsequent bits of a least-significant-bit-information bit sequence (Isbs[]) in order to obtain least signifi- cant bit values associated with the spectral values.

7. The audio decoder according to claim 6, wherein the audio decoder is configured to use (1140e, 1141e) a single bit of the least-significant-bit-information bitse- quence for respective spectral values for which the two or more most significant values and any intermediate bits, as far as intermediate bits are present, indicate a non-zero value, wherein the used single bit of the least-significant-bit-information bitsequence is used (1140f, 1140g, 1141f, 1141g) in order to obtain a least signifi- cant bit value; and

wherein the audio decoder is configured to use (1140e, 1141e) a single bit of the least-significant-bit-information bitsequence for respective spectral values for which the two or more most significant values and any intermediate bits, as far as intermediate bits are present, indicate a zero value, and for which the used single bit of the least-significant-bit-information bitsequence confirms the zero value; and

wherein the audio decoder is configured to use (1140e, 11401, 1141e, 1141i) two subsequent bits of the least-significant-bit-information bitsequence for respective spectral values for which the two or more most significant values and any inter- mediate bits, as far as intermediate bits are present, indicate a zero value, and for which a first of the used bits of the least-significant-bit-information bitsequence in- dicates a deviation from the zero value by a least significant bit value, wherein a second of the used bits of the least-significant-bit-information bitsequence deter- mines (1140j, 1141j) a sign of the respective spectral value.

8. The audio decoder according to one of claims 1 to 7, wherein the audio decoder is configured to decode (972; 1140a-1141j) least significant bits starting from a least significant bit associated with a lowest frequency spectral value and proceeding towards spectral values associated with increasingly higher frequencies,

such that spectral values are refined by least-significant-bit information in a range from a lowest frequency spectral value up to a spectral value for which a last least significant bit information is available, and such that spectral values having associ- ated frequencies higher than a frequency associated with the spectral value for which the last least significant bit information is available remain unrefined.

9. The audio decoder according to one of claims 1 to 8, wherein the audio decoder is configured to be switchable between

- a first mode (930,934,938,942,944,948) in which a decoding of spectral values in a higher frequency range is omitted in response to a signaling from the en- coder and in which least significant bits are decoded (934) for all spectral val- ues for which one or more most significant bits are decoded and which com- prise more bits than the most significant bits, and

- a second mode (950,954,958,962,968,972) in which one or more least signifi- cant bits associated with one or more of the spectral values are decoded (972), while no least significant bits are decoded for one or more other spectral values for which one or more most significant bits are decoded and which comprise more bits than the most significant bits.

10. The audio decoder according to claim 9, wherein the audio decoder is configured to evaluate a bitstream flag which is included in the encoded audio information in order to decide whether the audio decoder operates in the first mode or in the sec- ond mode.

11. The audio decoder according to one of claims 1 to 10, wherein the audio decoder is configured to jointly decode (950; 1110a-1110g) two or more most significant bits per spectral value for at least two spectral values (Xq[n],Xq[n+1]) on the basis of respective symbol codes,

wherein a respective symbol code represents two or more most significant bits per spectral value for at least two spectral values.

12. The audio decoder according to one of claims 1 to 11, wherein the audio decoder is configured to decode spectral values according to the following algorithm:

Decode the 2 most significant bits of both coefficients Xq(n) and Xq(n+1) ac- cording to:

numbits = 1 ;

do {

Get probabilities p from context c

Decode symbol sym with arithmetic decoding and probabilities p

Update context c

numbits++;

} while (sym==VAL_ESC)

Xq[n] = (sym & 3) « (numbits-2);

Xq[n+1] = (sym » 2) « (numbits-2);

Decode remaining bits except the least significant bit, if there are any remaining bits, according to:

for (b = 1 ; b < numbits-2; b++) {

Decode bit0

Xq[n] += bit0 « b

Decode bit1

Xq[n+1] += bit1 « b

}

Decode the sign of each coefficient, except if the most significant bit is zero and the remaining bits are zero according to:

if(Xq[n] !=0 ) {

Decode bit0

if (bit0 == 1) {

Xq[n] = -Xq[n];

}

}

if(Xq[n+1] !=0) {

Decode bit1

if (bit1 == 1) {

Xq[n+1] = -Xq[n+1];

}

}

Set all coefficients n >= lastnz to zero, wherein lastnz is obtained on the basis of a side information obtained from the encoded audio representation;

Finalize the arithmetic decoding and compute the number of unused bits;

if there are unused bits, decode nlsbs bits and store them in a data structure lsbs [ ] ;

then refine the coefficients (Xq(n),Xq(n+1)) if numbits[n]>2 using the decoded LSB bits according to:

k = 0;

for (n = 0; n < lastnz; n+=2) {

if (numbits[n] > 2) {

if (k == nlsbs) {

break;

}

bit0 = lsbs[k++];

if (bit0 == 1) {

if (Xq[n] > 0) {

Xq[n] += 1 ;

} else if (Xq[n] < 0) {

Xq[n] -= 1 ;

} else {

if (k == nlsbs) {

break;

}

bit1 = lsbs[k++];

Xq[n] = 1 - 2*bit1 ;

}

}

if (k == nlsbs) {

break;

}

bit0 = lsbs[k++];

if (bit0 == 1 ) {

if (Xq[n+1] > 0) {

Xq[n+1]+= 1 ;

} else if (Xq[n+1 ] < 0) {

Xq[n+ 1 ] -= 1 ;

} else {

if (k == nlsbs) {

break;

}

bit1 = lsbs[k++];

Xq[n+1] = 1 - 2*bit1 ;

}

}

}

}

13. An audio decoder (100;200;700) for providing a decoded audio information (112;212;712) on the basis of an encoded audio information (110;210;710), wherein the audio decoder is configured to obtain decoded spectral values (132;232;732; Xq[n], Xq[n+1]) on the basis of an encoded information (130;230) representing the spectral values,

wherein the audio decoder is configured to decode (950; 1110a-1110g) one or more most significant bits on the basis of respective symbol codes (sym) for a plu- rality of spectral values (Xq[0]...Xq[lastnz-1]), and to decode one or more least sig- nificant bits for one or more of the spectral values,

wherein the audio decoder is configured to be switchable between

- a first mode (930,934,938,942,944,948) in which a decoding of spectral values in a higher frequency range is omitted in response to a signaling from the en- coder and in which least significant bits are decoded (934) for all spectral val- ues for which one or more most significant bits are decoded and which com- prise more bits than the most significant bits, and

- a second mode (950,954,958,962,968,972) in which one or more least signifi- cant bits associated with one or more of the spectral values are decoded, while no least significant bits are decoded for one or more other spectral values for which one or more most significant bits have been decoded and which com- prise more bits than the most significant bits; and

wherein the audio decoder is configured to provide the decoded audio information using the spectral values.

14. The audio decoder according to claim 13, wherein the arithmetic decoding is con- figured to determine (950; 1110a-1110e) bit positions (numbits, numbits-1) of the one or more most significant bits and to allocate (1110f, 1110g) the one or more most significant bits determined by a symbol of the arithmetically encoded repre- sentation to the determined bit positions

15. The audio decoder according to one of claims 13 to 14, wherein the audio decoder is configured to decode (954; 1120a-1120e), for all spectral values for which one or more most significant bits have been decoded and which comprise more bits than the one or more most significant bits and a least significant bit, one or more intermediate bits, bit positions of which are between the least significant bit and the one or more most significant bits.

16. The audio decoder according to one of claims 13 to 15, wherein the audio decoder is configured to decode, when operating in the second mode, in a first decoding phase,

- one or more most significant bits per spectral value, and

- for all spectral values for which one or more most significant bits are decoded and which comprise more bits than the one or more most significant bits and a least significant bit, one or more intermediate bits, bit positions of which are be- tween the least significant bit and the one or more most significant bits, and - for all spectral values for which one or more most significant bits are decoded and for which the one or more most significant bits and any intermediate bits, as far as intermediate bits are present, indicate a non-zero value, signs; and

wherein the audio decoder is configured to selectively omit, when operating in the second mode, in the first decoding phase, a decoding of a sign for spectral values for which the one or more most significant values and any intermediate bits, as far as intermediate bits are present, indicate a zero value, and

wherein the audio decoder is configured to selectively obtain, when operating in the second mode, in a second decoding phase which follows the first decoding phase, sign information for spectral values for which the one or more most signifi- cant values and any intermediate bits, as far as intermediate bits are present, indi- cate a zero value and for which a least significant bit information indicates a non- zero value.

17. The audio decoder according to one of claims 13 to 16, wherein the audio decoder is configured to sequentially use subsequent bits of a least-significant-bit- information bit sequence in order to obtain least significant bit values associated with the spectral values when operating in the second mode.

18. The audio decoder according to claim 17, wherein the audio decoder is configured to use, when operating in the second mode, a single bit of the least-significant-bit- information bitsequence for respective spectral values for which the one or more most significant values and any intermediate bits, as far as intermediate bits are present, indicate a non-zero value, wherein the used single bit of the least- significant-bit-information bitsequence is used in order to obtain a least significant bit value; and

wherein the audio decoder is configured to use, when operating in the second mode, a single bit of the least-significant-bit-information bitsequence for respective spectral values for which the one or more most significant values and any inter- mediate bits, as far as intermediate bits are present, indicate a zero value, and for which the used single bit of the least-significant-bit-information bitsequence con- firms the zero value; and

wherein the audio decoder is configured to use, when operating in the second mode, two subsequent bits of the least-significant-bit-information bitsequence for respective spectral values for which the one or more most significant values and any intermediate bits, as far as intermediate bits are present, indicate a zero value, and for which a first of the used bits of the least-significant-bit-information bitse- quence indicates a deviation from the zero value by a least significant bit value, wherein a second of the used bits of the least-significant-bit-information bitse- quence determines a sign of the respective spectral value.

19. The audio decoder according to one of claims 13 to 18, wherein the audio decoder is configured to decode, when operating in the second mode, least significant bits starting from a least significant bit associated with a lowest frequency spectral val- ue and proceeding towards spectral values associated with increasingly higher frequencies,

such that spectral values are refined by least-significant-bit information in a range from a lowest frequency spectral value up to a spectral value for which a last least significant bit information is available, and such that spectral values having associ- ated frequencies higher than a frequency associated with the spectral value for which the last least significant bit information is available remain unrefined.

20. The audio decoder according to one of claims 13 to 19, wherein the audio decoder is configured to evaluate a bitstream flag which is included in the encoded audio information in order to decide whether the audio decoder operates in the first mode or in the second mode.

21. The audio decoder according to one of claims 13 to 20, wherein the audio decoder is configured to obtain (934) intermediate bits, bit positions of which are between the least significant bit and the one or more most significant bits, and the least sig- nificant bit associated with a given spectral value from a contiguous bit sequence in the first mode, and

wherein the audio decoder is configured to obtain (954) intermediate bits, bit posi- tions of which are between the least significant bit and the one or more most signif- icant bits, and the least significant bit associated with a given spectral value (972) from separate bit sequences or from separate, non-contiguous bit locations of a bit sequence in the second mode.

22. The audio decoder according to one of claims 13 to 21, wherein the audio decode is configured to selectively obtain (938) a sign information associated with a spec- tral value only after a decoding of the one or or most significant bits, any interme- diate bits, bit positions of which are between the least significant bit and the one o more most significant bits, and the least significant bit associated with a given spectral value in the first mode, in dependence on whether the one or more most significant bits, the intermediate bits and the least significant bit indicate a zero value or not, and

wherein the audio decoder is configured to selectively obtain (958; 1130a-1131d) a sign information associated with a spectral value after a decoding of the one or ore most significant bits and any intermediate bits, bit positions of which are between the least significant bit and the one or more most significant bits, but before a least significant bit associated with a given spectral value is decoded in the second mode, in dependence on whether the one or more most significant bits and the in- termediate bits indicate a zero value or not.

23. An audio encoder (300;400;500;600) for providing an encoded audio information (312;412;512;612) on the basis of an input audio information (310;410;510;610), wherein the audio encoder is configured to obtain (620,630,640,650,660) spectral values (330;662;Xq[n]) representing an audio content of the input audio infor- mation, and

wherein the audio encoder is configured to encode (670;800) at least a plurality of the spectral values, in order to obtain an encoded information (350,450,550,672; sym,lsbs[]) representing the spectral values;

wherein the audio encoder is configured to jointly encode (878,886,890;

1000a, 1020a, 1040a-1040d) two or more most significant bits per spectral value, to obtain respective symbol codes (sym) for a set of spectral values (Xq[0]...Xq[lastnz-1]) using an arithmetic encoding,

wherein a respective symbol code (sym) represents two or more most significant bits per spectral value for one or more spectral values,

wherein the audio encoder is configured to encode (882;898; 1010a-1010e, 1011a- 1011e) one or more least significant bits associated with one or more of the spec- tral values in dependence on a bit budget available,

such that one or more least significant bits associated with one or more of the spectral values are encoded, while no least significant bits are encoded for one or more other spectral values for which two or more most significant bits are encoded and which comprise more bits than the two or more most significant bits; and

wherein the audio encoder is configured to provide the encoded audio information using the encoded information representing the spectral values.

24. The audio encoder according to claim 23, wherein the arithmetic encoding is con- figured to determine (878; 1000a) bit positions (numbits, numbits-1) of the at least two most significant bits and include (886,1020a) into the arithmetically encoded representation an information describing the bit positions.

25. The audio encoder according to claim 23 or claim 24, wherein the audio encoder is configured to map (890; 1040a-1040d) at least two most significant bits of the at least one spectral value (Xq[n,Xq[n+1) onto one symbol (sym) of an arithmetically encoded representation, which represents the at least two most significant bits of the at least one spectral value.

26. The audio encoder according to one of claims 23 to 25, wherein the audio encoder is configured to encode (892; 1050a-1050c), for all spectral values for which two or more most significant bits are encoded and which comprise more bits than the two or more most significant bits and a least significant bit, one or more intermediate bits, bit positions of which are between the least significant bit and the two or more most significant bits.

27. The audio encoder according to one of claims 23 to 26, wherein the audio encoder is configured to encode, in a first encoding phase,

- two or more most significant bits per spectral value

(878,886,890; 1000a, 1020a, 1040a-1040d), and

- for all spectral values for which two or more most significant bits are encoded and which comprise more bits than the two or more most significant bits and a least significant bit, one or more intermediate bits, bit positions of which are be- tween the least significant bit and the two or more most significant bits (892; 1050a-1050c), and

- for all spectral values for which two or more most significant bits are encoded and for which the two or more most significant bits and any intermediate bits, as far as intermediate bits are present, indicate a non-zero value, signs (894;1060a-1061c); and

wherein the audio encoder is configured to selectively omit (1060a, 1061a), in the first encoding phase, an encoding of a sign for spectral values for which the two or more most significant values and any intermediate bits, as far as intermediate bits are present, indicate a zero value, and

wherein the audio encoder is configured to selectively encode (898), in a second encoding phase, sign information (1010e, 1011e) for spectral values for which the two or more most significant values and any intermediate bits, as far as intermedi- ate bits are present, indicate a zero value and for which a least significant bit in- formation indicates a non-zero value.

28. The audio encoder according to one of claims 23 to 27, wherein the audio encoder is configured to only include (882,898; 1010c-1010e, 1011c-1011e) a sign infor- mation into the encoded audio representation for spectral values which only differ from zero by a least significant bit if the least significant bit of such spectral values is actually encoded.

29. The audio encoder according to one of claims 23 to 28, wherein the audio encoder is configured to sequentially provide subsequent bits of a least-significant-bit- information bit sequence (Isbs[]) in order to encode least significant bit values as- sociated with the spectral values.

30. The audio encoder according to claim 29, wherein the audio encoder is configured to provide (882,898; 1010a, 1010b, 1011a,1011b) a single bit (bit) of the least- significant-bit-information bitsequence (lsbs[]) for respective spectral values for which the two or more most significant values and any intermediate bits, as far as intermediate bits are present, indicate a non-zero value, wherein the used single bit of the least-significant-bit-information bitsequence is used in order to encode a least significant bit value; and

wherein the audio encoder is configured to provide

(882, 898; 1010a, 1010b, 1011a, 1011b) a single bit of the least-significant-bit- information bitsequence for respective spectral values for which the two or more most significant values and any intermediate bits, as far as intermediate bits are present, indicate a zero value, and for which the provided single bit (bit) of the least-significant-bit-information bitsequence confirms the zero value; and wherein the audio encoder is configured to provide (882,898;

1010a, 1010b, 1010d, 1010e, 1011a, 1011b, 1011d, 1011e) two subsequent bits of the least-significant-bit-information bitsequence for respective spectral values for which the two or more most significant values and any intermediate bits, as far as intermediate bits are present, indicate a zero value, and for which a first of the pro- vided bits of the least-significant-bit-information bitsequence indicates a deviation from the zero value by a least significant bit value, wherein a second of the provid- ed bits of the least-significant-bit-information bitsequence encodes a sign of the re- spective spectral value.

31. The audio encoder according to one of claims 23 to 30, wherein the audio encoder is configured to encode (882,898; 1140a-1141j) least significant bits starting from a least significant bit associated with a lowest frequency spectral value and proceed- ing towards spectral values associated with increasingly higher frequencies,

such that encoded information for refining spectral values by least-significant-bit in- formation is provided in a range from a lowest frequency spectral value up to a spectral value for which a last least significant bit information is provided, and such that no encoded information for refining spectral values by least-significant-bit information is provided for spectral values having associated frequencies higher than a frequency associated with the spectral value for which the last least signifi- cant bit information is provided.

32. The audio encoder according to one of claims 23 to 31, wherein the audio encoder is configured to be switchable between

- a first mode (840,844,848,852,856,860,864,868,869) in which an encoding of non-zero spectral values in a higher frequency range is omitted in case that an available bit budget is used up by an encoding of spectral values in a lower frequency range and in which least significant bits are encoded (860) for all

spectral values for which one or more most significant bits are encoded (848,852,856) and which comprise more bits than the most significant bits, and

- a second mode (870,874,878,882,886,890,892,894,896,898) in which one or more least significant bits associated with one or more of the spectral values are encoded (898), while no least significant bits are encoded for one or more other spectral values for which one or more most significant bits are encoded and which comprise more bits than the most significant bits.

33. The audio encoder according to claim 32, wherein the audio encoder is configured to provide a bitstream flag which is included in the encoded audio information in order to indicate whether the audio encoder operates in the first mode or in the second mode.

34. The audio encoder according to one of claims 23 to 33, wherein the audio encoder is configured to jointly encode (878,886,890; 1000a, 1020a, 1040a-1040d) two or more most significant bits per spectral value for at least two spectral values (Xq[n],Xq[n+1]) using respective symbol codes (sym),

wherein a respective symbol code represents two or more most significant bits per spectral value for at least two spectral values.

35. The audio encoder according to one of claims 23 to 34, wherein the audio encoder is configured determine an actual highest-frequency non-zero spectral value and to encode at least two or more most significant bits of all non-zero spectral values or of all non-zero groups of spectral values.

36. The audio encoder according to one of claims 23 to claim 35, wherein the audio encoder is configured to encode (878,886,890,892) all bits except for a least signif- icant bit for all non-zero spectral values, and

wherein the audio encoder is configured to encode (882,898) least significant bits for spectral values until a bit budget is exhausted.

37. The audio encoder according to one of claims 23 to 36, wherein the audio encoder is configured to obtain (810; 814,818,82) a gain information which determines

quantization steps of a quantization (660) of spectral values, and which determines a bit demand for encoding the quantized spectral values.

38. An audio encoder (300;400;500;600) for providing an encoded audio information (312;412;512;612) on the basis of an input audio information (310;410;510;610), wherein the audio encoder is configured to obtain (620,630,640,650,660) spectral values representing an audio content of the input audio information, and wherein the audio encoder is configured to encode (670;800) at least a plurality of the spectral values, in order to obtain an encoded information (350,450,550,672; sym.lsbs[]) representing the spectral values;

wherein the audio encoder is configured to encode (882;898; 1010a-1010e, 1011a- 1011e) one or more most significant bits, to obtain respective symbol codes for a plurality of the spectral values (Xq[0]...Xq[lastnz-1]), and to encode one or more least significant bits for one or more of the spectral values,

wherein a respective symbol code (sym) represents one or more most significant bits values for one or more spectral values (Xq[n], Xq[n+1]),

wherein the audio encoder is configured to be switchable between

- a first mode (840,844,848,852,856,860,864,868,869) in which an encoding of non-zero spectral values in a higher frequency range is omitted in case that an available bit budget is used up by an encoding of spectral values in a lower frequency range and in which least significant bits are encoded (860) for all spectral values for which one or more most significant bits are encoded (848,852,856) and which comprise more bits than the most significant bits, and

- a second mode (870,874,878,882,886,890,892,894,896,898) in which one or more least significant bits associated with one or more of the spectral values are encoded (898), while no least significant bits are encoded for one or more other spectral values for which one or more most significant bits are encoded and which comprise more bits than the most significant bits;

wherein the audio encoder is configured to provide the encoded audio information using the encoded information representing the spectral values.

39. The audio encoder according to claim 38, wherein the audio encoder is configured to encode (878,886,890) at least one or more most significant bits of all non-zero spectral values or of all non-zero groups of spectral values in the second mode.

40. The audio encoder according to one of claims 38 to 39, wherein the audio encoder is configured to limit, when operating in the first mode, a frequency range, for which spectral values are encoded, in case that a bit budget is insufficient, such that one or more spectral values are left unconsidered in the encoding of spectral values.

41. The audio encoder according to claim 40, wherein the audio encoder is configured to determine, when operating in the first mode, a maximum frequency value and to encode (848,852,856,860), when operating in the first mode, spectral values up to the maximum frequency and to leave, when operating in the first mode, spectral values above the maximum frequency unencoded even if the spectral values are non-zero,

wherein the audio encoder is configured to select, when operating in the first mode, the maximum frequency value in dependence on a computation or estima- tion of a bit demand for encoding all spectral values, such that a number of spec- tral values to be encoded is reduced if the computed or estimated bit demand would exceed a bit budget, and

wherein the audio encoder is configured to determine, when operating in the sec- ond mode, the maximum frequency value and to encode (878,882,886,890,898) when operating in the second mode, spectral values up to the maximum frequency and to leave, when operating in the second mode, spectral values above the max- imum frequency unencoded,

wherein the audio encoder is configured to select, when operating in the second mode, the maximum frequency value such that at least one or more most signifi- cant bits of all non-zero spectral values or of all non-zero groups of spectral values are encoded and such that at most zero-valued spectral values are left unencoded.

42. The audio encoder according to claim 40 or claim 41, wherein the audio encoder is configured to include an information (lastnz) describing the maximum frequency in- to the encoded audio information.

43. The audio encoder according to one of claims 38 to 42, wherein the audio encoder is configured to make a mode decision (830) whether to use the first mode or the second mode in dependence on an available bit rate.

44. The audio encoder according to one of claims 38 to 43, wherein the audio encoder is configured to make a mode decision (830) whether to use the first mode or the second mode in dependence on a number of spectral values or groups of spectral values which comprise, in addition to one or more most significant bits encoded in a most-significant-bit-encoding step, one or more least significant bits, an encoding of which can selectively be omitted in dependence on a bit demand and a bit budget.

45. The audio encoder according to one of claims 38 to 44, wherein the audio encoder is configured to include a bitstream flag in the encoded audio information indicating whether the audio encoder operates in the first mode or in the second mode.

46. The audio encoder according to one of claims 38 to 45, wherein the audio encoder is configured to encode (860) intermediate bits, bit positions of which are between the least significant bit and the one or more most significant bits, and the least sig- nificant bit associated with a given spectral value into a contiguous bit sequence in the first mode, and

wherein the audio encoder is configured to encode (892) intermediate bits, bit posi- tions of which are between the least significant bit and the one or more most signif- icant bits, and the least significant bit associated with a given spectral value (882,898) into separate bit sequences or into separate, non-contiguous bit loca- tions of a bit sequence in the second mode.

47. The audio encoder according to one of claims 38 to 46, wherein the audio encoder is configured to encode (864), when operating in the first mode, a sign information associated with a spectral value in a bit sequence which is associated with inter- mediate bits, bit positions of which are between the least significant bit and the one or more most significant bits, and least significant bits, and

wherein the audio encoder is configured to selectively encode, when operating in the second mode, a sign information associated with a spectral value in a bit se- quence which is associated with intermediate bits, bit positions of which are be- tween the least significant bit and the one or more most significant bits, and sign information (894) or in a bit sequence (Isbs[]) associated with least significant bits and sign information (882,898), such that sign information for spectral values which deviate from zero only by a least significant bit value are encoded in the bit sequence associated with least significant bits and sign information.

48. An audio encoder (300;400;500;600) for providing an encoded audio information (312;412;512;612) on the basis of an input audio information(310;410;510;610), wherein the audio encoder is configured to obtain (620,630,640,650,660) spectral values (330;662;Xq[n]) representing an audio content of the input audio infor- mation, and

wherein the audio encoder is configured to encode (670;800) at least a plurality of the spectral values, in order to obtain an encoded information (350,450,550,672; sym.Isbs[]) representing the spectral values;

wherein the audio encoder is configured to obtain (810,814,818,822) a gain infor- mation which determines quantization steps of a quantization of spectral values, and which determines a bit demand for encoding the quantized spectral values (330;662;Xq[n]);

wherein the audio encoder is configured to encode (878,886,890;

1000a, 1020a, 1040a-1040d) one or more most significant bits using respective symbol codes (sym) for a plurality of the spectral values (Xq[0]...Xq[lastnz-1]) us- ing an arithmetic encoding, and to encode one or more least significant bits for one or more of the spectral values,

wherein a respective symbol code (sym) represents one or more most significant bits per spectral value for one or more spectral values,

wherein the audio encoder is configured to encode (882;898;1010a-1010e, 1011a- 1011e) one or more least significant bits associated with one or more of the spec- tral values in dependence on a bit budget available,

such that one or more least significant bits associated with one or more of the spectral values are encoded, while no least significant bits are encoded for one or more other spectral values for which one or more most significant bits are encoded and which comprise more bits than the one or more most significant bits ; and

wherein the audio encoder is configured to provide the encoded audio information using the encoded information representing the spectral values.

49. The audio encoder of claim 48, wherein the audio encoder is configured to obtain (810) a first estimate of the gain information based on an energy of groups of spectral values,

to quantize (814) set of spectral values using the first estimate of gain information,

to compute or estimate (818) a number of bits needed to encode the set of spectral values quantized using the first estimate of gain information or using a refined gain information, and

to decide (830) whether to use the first mode or the second mode in dependence on a number of bits needed.

50. The audio encoder according to claim 48 or claim 49,

wherein the audio encoder is configured to be switchable between

- a first mode in which an encoding of non-zero spectral values in a higher fre- quency range is omitted in case that an available bit budget is used up by en- coded spectral values in a lower frequency range and in which least significant bits are encoded for all spectral values for which one or more most significant bits are encoded and which comprise more bits than the most significant bits, and

- a second mode in which one or more least significant bits associated with one or more of the spectral values are encoded, while no least significant bits are encoded for one or more other spectral values for which one or more most sig- nificant bits are encoded and which comprise more bits than the most signifi- cant bits; and

wherein the audio encoder is configured to decide whether to use the first mode or the second mode in dependence on the number of bits needed and in dependence

on a criterion which indicates how many spectral values comprise more bits than the one or more most significant bits.

51. The audio encoder according to claim 48 or claim 49,

wherein the audio encoder is configured to be switchable between

- a first mode in which an encoding of non-zero spectral values in a higher fre- quency range is omitted in case that an available bit budget is used up by en- coded spectral values in a lower frequency range and in which least significant bits are encoded for all spectral values for which one or more most significant bits are encoded and which comprise more bits than the most significant bits, and

- a second mode in which one or more least significant bits associated with one or more of the spectral values are encoded, while no least significant bits are encoded for one or more other spectral values for which one or more most sig- nificant bits are encoded and which comprise more bits than the most signifi- cant bits; and

wherein the audio encoder is configured to decide whether to use the first mode or the second mode in dependence on the number of bits needed and in dependence on a bitrate, such that the second mode is chosen if a bitrate is larger than or equal to a threshold bitrate and if a computed or estimated number of bits needed to en- code the set of spectral values is higher than a bit budget.

52. The audio encoder according to one of claims 38 to 51, wherein the arithmetic en- coding is configured to determine bit positions of the one or more most significant bits and include into the arithmetically encoded representation an information de- scribing the bit positions.

53. The audio encoder according to one of claims 38 to 52, wherein the audio encoder is configured to map at least two most significant bits of the at least one spectral value onto one symbol of an arithmetically encoded representation, which repre- sents the at least two most significant bits of the at least one spectral value.

54. The audio encoder according to one of claims 38 to 53, wherein the audio encoder is configured to encode, for all spectral values for which one or more most signifi- cant bits are encoded and which comprise more bits than the one or more most significant bits and a least significant bit, one or more intermediate bits, bit posi- tions of which are between the least significant bit and the one or more most signif- icant bits.

55. The audio encoder according to one of claims 38 to 54, wherein the audio encoder is configured to encode, in a first encoding phase,

- one or more most significant bits per spectral value, and

- for all spectral values for which one or more most significant bits are encoded and which comprise more bits than the one or more most significant bits and a least significant bit, one or more intermediate bits, bit positions of which are be- tween the least significant bit and the one or more most significant bits, and - for all spectral values for which one or more most significant bits are encoded and for which the one or more most significant bits and any intermediate bits, as far as intermediate bits are present, indicate a non-zero value, signs; and

wherein the audio encoder is configured to selectively omit, in the first encoding phase, an encoding of a sign for spectral values for which the one or more most significant values and any intermediate bits, as far as intermediate bits are pre- sent, indicate a zero value, and

wherein the audio encoder is configured to selectively encode, in a second encod- ing phase which follows the first encoding phase, sign information for spectral val- ues for which the one or more most significant values and any intermediate bits, as far as intermediate bits are present, indicate a zero value and for which a least significant bit information indicates a non-zero value.

56. The audio encoder according to one of claims 38 to 55, wherein the audio encoder is configured to only include a sign information into the encoded audio representa- tion for spectral values which only differ from zero by a least significant bit if the least significant bit of such spectral values is actually encoded.

57. The audio encoder according to one of claims 38 to 56, wherein the audio encoder is configured to sequentially provide subsequent bits of a least-significant-bit- information bit sequence in order to encode least significant bit values associated with the spectral values.

58. The audio encoder according to claim 57, wherein the audio encoder is configured to provide a single bit of the least-significant-bit-information bitsequence for re- spective spectral values for which the one or more most significant values and any intermediate bits, as far as intermediate bits are present, indicate a non-zero value, wherein the used single bit of the least-significant-bit-information bitsequence is used in order to encode a least significant bit value; and

wherein the audio encoder is configured to provide a single bit of the least- significant-bit-information bitsequence for respective spectral values for which the one or more most significant values and any intermediate bits, as far as intermedi- ate bits are present, indicate a zero value, and for which the provided single bit of the least-significant-bit-information bitsequence confirms the zero value; and wherein the audio encoder is configured to provide two subsequent bits of the least-significant-bit-information bitsequence for respective spectral values for which the one or more most significant values and any intermediate bits, as far as intermediate bits are present, indicate a zero value, and for which a first of the pro- vided bits of the least-significant-bit-information bitsequence indicates a deviation from the zero value by a least significant bit value, wherein a second of the provid- ed bits of the least-significant-bit-information bitsequence encodes a sign of the re- spective spectral value.

59. The audio encoder according to one of claims 38 to 58, wherein the audio encoder is configured to encode least significant bits starting from a least significant bit as- sociated with a lowest frequency spectral value and proceeding towards spectral values associated with increasingly higher frequencies,

such that encoded information for refining spectral values by least-significant-bit in- formation is provided in a range from a lowest frequency spectral value up to a spectral value for which a last least significant bit information is provided, and such that no encoded information for refining spectral values by least-significant-bit information is provided for spectral values having associated frequencies higher than a frequency associated with the spectral value for which the last least signifi- cant bit information is provided.

60. The audio encoder according to one of claims 38 to 59, wherein the audio encoder is configured to be switchable between

- a first mode in which an encoding of non-zero spectral values in a higher fre- quency range is omitted in case that an available bit budget is used up by en- coded spectral values in a lower frequency range and in which least significant bits are encoded for all spectral values for which one or more most significant bits are encoded and which comprise more bits than the most significant bits, and

- a second mode in which one or more least significant bits associated with one or more of the spectral values are encoded, while no least significant bits are encoded for one or more other spectral values for which one or more most sig- nificant bits are encoded and which comprise more bits than the most signifi- cant bit.

61. The audio encoder according to claim 60, wherein the audio encoder is configured to provide a bitstream flag which is included in the encoded audio information in order to indicate whether the audio encoder operates in the first mode or in the second mode.

62. The audio encoder according to one of claims 38 to 61 , wherein the audio encoder is configured to jointly encode one or more most significant bits per spectral value for at least two spectral values using respective symbol codes,

wherein a respective symbol code represents one or more most significant bits per spectral value for at least two spectral values.

63. The audio encoder according to one of claims 38 to 62, wherein the audio encoder is configured to determine, when operating in the second mode, an actual highest- frequency non-zero spectral value and to encode at least one or more most signifi- cant bits of all non-zero spectral values or of all non-zero groups of spectral val- ues.

64. The audio encoder according to one of claims 38 to 63, wherein the audio encoder is configured to encode, when operating in the second mode, all bits except for a least significant bit for all non-zero spectral values, and

wherein the audio encoder is configured to encode least significant bits for spectral values until a bit budget is exhausted.

65. The audio encoder according to one of claims 38 to 64, wherein the audio encoder is configured to obtain a gain information which determines quantization steps of a quantization of spectral values, and which determines a bit demand for encoding the quantized spectral values.

66. A method for providing a decoded audio information (112; 212; 712) on the basis of an encoded audio information (110;210;710),

wherein the method comprises obtaining decoded spectral values (132;232;732; Xq[n], Xq[n+1]) on the basis of an encoded information (130; 230) representing the spectral values,

wherein the method comprises jointly decoding (950; 1110a-1110g) two or more most significant bits per spectral value on the basis of respective symbol codes (sym) for a set of spectral values using an arithmetic decoding,

wherein a respective symbol code (sym) represents two or more most significant bits per spectral value for one or more spectral values,

wherein the method comprises decoding (972; 1140a-1141j) one or more least significant bits associated with one or more of the spectral values in dependence on how much least significant bit information is available,

such that one or more least significant bits associated with one or more of the spectral values are decoded, while no least significant bits are decoded for one or more other spectral values for which one or more most significant bits are decoded and which comprise more bits than the one or more most significant bits; and

wherein the method comprises providing the decoded audio information using the spectral values.

67. A method for providing a decoded audio information (112;212;712) on the basis of an encoded audio information (110;210;710),

wherein the method comprises obtaining decoded spectral values (132;232;732; Xq[n], Xq[n+1]) on the basis of an encoded information (130;230) representing the spectral values,

wherein the method comprises decoding (950; 1110a-1110g) one or more most significant bits on the basis of respective symbol codes (sym) for a plurality of spectral values (Xq[0]...Xq[lastnz-1]), and

decoding one or more least significant bits for one or more of the spectral values,

wherein the method comprises selecting between

- a first mode (930,934,938,942,944,948) in which a decoding of spectral values in a higher frequency range is omitted in response to a signaling from the en- coder and in which least significant bits are decoded (934) for all spectral val- ues for which one or more most significant bits are decoded and which com- prise more bits than the most significant bits, and

- a second mode (950,954,958,962,968,972) in which one or more least signifi- cant bits associated with one or more of the spectral values are decoded, while no least significant bits are decoded for one or more other spectral values for which one or more most significant bits have been decoded and which com- prise more bits than the most significant bits; and

wherein the method comprises providing the decoded audio information using the spectral values.

68. A method for providing an encoded audio information (312;412;512;612) on the basis of an input audio information (310;410;510;610),

wherein the method comprises obtaining (620,630,640,650,660) spectral values (330;662;Xq[n]) representing an audio content of the input audio information, and wherein the method comprises encoding (670;800) at least a plurality of the spec- tral values, in order to obtain an encoded information (350,450,550,672; sym,Isbs[]) representing the spectral values;

wherein the method comprises jointly encoding (878,886,890;

1000a, 1020a, 1040a-1040d) two or more most significant bits per spectral value, to obtain respective symbol codes (sym) for a set of spectral values (Xq[0]...Xq[lastnz-1]), using an arithmetic encoding,

wherein a respective symbol code (sym) represents two or more most significant bits per spectral value for one or more spectral values,

wherein the method comprises encoding (882;898; 1010a-1010e, 1011a-1011e) one or more least significant bits associated with one or more of the spectral val- ues in dependence on a bit budget available,

such that one or more least significant bits associated with one or more of the spectral values are encoded, while no least significant bits are encoded for one or more other spectral values for which two or more most significant bits are encoded and which comprise more bits than the two or more most significant bits; and

wherein the method comprises providing the encoded audio information using the encoded information representing the spectral values.

69. A method for providing an encoded audio information (312;412;512;612) on the basis of an input audio information (310;410;510;610),

wherein the method comprises obtaining (620,630,640,650,660) spectral values representing an audio content of the input audio information, and

wherein the method comprises encoding (670;800) at least a plurality of the spec- tral values, in order to obtain an encoded information (350,450,550,672; sym,Isbs[]) representing the spectral values;

wherein the method comprises encoding (882;898;1010a-1010e, 1011a-1011e) one or more most significant bits, to obtain respective symbol codes for a plurality of the spectral values (Xq[0]...Xq[lastnz-1]), and encoding one or more least signif- icant bits for one or more of the spectral values,

wherein a respective symbol code (sym) represents one or more most significant bits values for one or more spectral values (Xq[n], Xq[n+1]),

wherein the method comprises selecting between

- a first mode (840,844,848,852,856,860,864,868,869) in which an encoding of non-zero spectral values in a higher frequency range is omitted in case that an available bit budget is used up by an encoding of spectral values in a lower frequency range and in which least significant bits are encoded (860) for all spectral values for which one or more most significant bits are encoded (848,852,856) and which comprise more bits than the most significant bits, and

- a second mode (870,874,878,882,886,890,892,894,896,898) in which one or more least significant bits associated with one or more of the spectral values are encoded (898), while no least significant bits are encoded for one or more other spectral values for which one or more most significant bits are encoded and which comprise more bits than the most significant bits;

wherein the method comprises providing the encoded audio information using the encoded information representing the spectral values.

70. A method for providing an encoded audio information (312;412;512;612) on the basis of an input audio information (310;410;510;610),

wherein the method comprises obtaining (620,630,640,650,660) spectral values (330; 662; Xq[n]) representing an audio content of the input audio information, and wherein the method comprises encoding (670;800) at least a plurality of the spec- tral values, in order to obtain an encoded information (350,450,550,672; sym, Isbs[]) representing the spectral values;

wherein the method comprises obtaining (810,814,818,822) a gain information which determines quantization steps of a quantization of spectral values, and which determines a bit demand for encoding the quantized spectral values;

wherein the method comprises encoding (878,886,890; 1000a, 1020a, 1040a- 1040d) one or more most significant bits using respective symbol codes (sym) for a plurality of the spectral values (Xq[0]...Xq[lastnz-1]) using an arithmetic encod- ing, and encoding one or more least significant bits for one or more of the spectral values,

wherein a respective symbol code (sym) represents one or more most significant bits per spectral value for one or more spectral values,

wherein the method comprises encoding (882;898; 1010a-1010e, 1011a-1011e) one or more least significant bits associated with one or more of the spectral val- ues in dependence on a bit budget available,

such that one or more least significant bits associated with one or more of the spectral values are encoded, while no least significant bits are encoded for one or more other spectral values for which one or more most significant bits are encoded and which comprise more bits than the one or more most significant bits ; and

wherein the method comprises providing the encoded audio information using the encoded information representing the spectral values.

71. A computer program for performing the method according to one of claims 66 to 70 when the computer program runs on a computer.

72. An encoded audio representation, comprising:

an encoded information (130;230) representing spectral values; and

a flag indicating whether an audio decoder should work

- in a first mode (930,934,938,942,944,948) in which a decoding of spectral val- ues in a higher frequency range is omitted in response to a signaling from the encoder and in which least significant bits are decoded (934) for all spectral values for which one or more most significant bits are decoded and which comprise more bits than the most significant bits, or

- in a second mode (950,954,958,962,968,972) in which one or more least sig- nificant bits associated with one or more of the spectral values are decoded, while no least significant bits are decoded for one or more other spectral values for which one or more most significant bits have been decoded and which comprise more bits than the most significant bits.