Encoding an Information Signal

• US 20080221905A1
• Filed: 10/18/2007
• Published: 09/11/2008
• Est. Priority Date: 10/18/2006
• Status: Active Grant

• Current Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Original Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Inventors: Schnell, Markus, Lutzky, Manfred, Schuldt, Michael, Jander, Manuel
• Granted Patent: US 8,041,578 B2
• Time in Patent Office: Days
• US Class Current: 704/500
• CPC Class Codes: G10L 19/025 Detection of transients or attacks for time/frequency resolution switching
• CPC Class Codes: G10L 21/038 using band spreading techniques

Abstract

The transient problem may be sufficiently addressed, and for this purpose, a further delay on the side of the decoding may be reduced if a new SBR frame class is used wherein the frame boundaries are not shifted, i.e. the grid boundaries are still synchronized with the frame boundaries, but wherein a transient position indication is additionally used as a syntax element so as to be used, on the encoder and/or decoder sides, within the frames of these new frame class for determining the grid boundaries within these frames.

Claims

1. An encoder comprising

a means (104, 106) for encoding a low-frequency portion of an information signal in units of frames (902) of the information signal;

a means (118) for localizing transients within the information signal;

a means (116) for, as a function of the localization, associating a respective reconstruction mode from among at least two possible reconstruction modes (FIXFIX, LD_TRAN) with the frames of the information signal, and, for frames which have associated therewith a first one (LD_TRAN) of the at least two possible reconstruction modes, associating a respective transient position indication (bs_transient_position) with these frames; and

a means (110, 112, 114) for generating a representation of a spectral envelope of a high-frequency portion of the information signal in a temporal grid which depends on reconstruction modes associated with the frames, such that frames which have the first one of the at least two possible reconstruction modes associated therewith, the frame boundaries (902a, 902b) of these frames (902) coincide with grid boundaries of the grid (222a, 220, 222b), and the grid boundaries of the grid within these frames depend on the transient position indication (T); and

a means (108) for combining the encoded low-frequency portion, the representation of the spectral envelope and information on the associated reconstruction modes and the transient position indications into an encoded information signal.

2. The encoder as claimed in claim 1, wherein the means for generating is configured such that the grid boundaries within the frame, which have the first one of the at least two possible reconstruction modes associated therewith, are located such that they specify at least a first grid area (220) whose position within the respective frame depends on the transient position indication, and whose temporal extension is smaller than ⅓

of a length of the frames, as well as a second and/or a third grid area(s) (222a, 222b) which take(s) up the remaining part of the respective frame from the first grid area to the frame boundary (902a, 902b), which is leading in terms of time and/or trailing in terms of time, of the respective frame.

3. The encoder as claimed in claim 2, wherein the means for generating and the means for combining are configured to introduce, for a frame (404) having the first reconstruction mode associated with it which comprises three grid areas (410, 412, 414) and wherein the first grid area (412) among the three grid areas is closer to a preceding frame than a predetermined value, one or several spectral envelope values describing the spectral envelope with a respective frequency resolution, only for the first and third grid areas (412, 414), into the encoded information signal, and to introduce no spectral envelope value into the encoded information signal for the second grid area (410) of this frame (404).

4. The encoder as claimed in claims 2 or 3, wherein the means for generating and the means for combining are configured to introduce, for a frame (502) having the first reconstruction mode associated with it, which comprises only two grid areas (502a, 502b) and wherein the first grid area (502b) borders on the frame boundary which is trailing in terms of time, one or several spectral envelope values, for both grid areas, said one or several spectral envelope value(s) describing the spectral envelope with a respective frequency resolution, into the encoded information signal, and to also use, for determining the spectral envelope value(s) for the first grid area (502b), parts of the information signal located in the extension grid area (504b′

) in the subsequent frame (504) which borders on the trailing frame boundary, and to shorten a grid area (504a′

), which is leading in terms of time, of the subsequent frame (504) as is specified by the reconstruction mode of the subsequent frame, so as to start only at the extension grid area (504b′

).

5. The encoder as claimed in claims 3 or 4, wherein the means for generating and the means for combining are configured to introduce one or several spectral envelope values into the encoded information signal for a frame having the second reconstruction mode associated with it or having the first reconstruction mode associated with it, but for which neither the condition that it comprises three grid areas and that, at the same time, the first grid area among the three grid areas is located closer to the preceding frame than the predetermined value, nor the condition that it comprises only two grid areas and that, at the same time, the first grid area borders on the frame boundary which is trailing in terms of time, are fulfilled, for each grid area of this frame.

6. The encoder as claimed in claim 2, wherein the means for generating is configured such that the first grid area (220) borders on the frame boundary (902a), leading in terms of time, of the respective frame if there is no second grid area (222a), and wherein the first grid area (220) borders on the frame boundary (902b), trailing in terms of time, of the respective frame if no third grid area (222b) exists.

7. The encoder as claimed in any of the previous claims, wherein the means for generating is configured such that the grid boundaries within frames which have the second (FIXFIX) of the at least two possible reconstruction modes associated with them are located such that they are equally distributed over time, so that these frames only comprise one grid area or are subdivided into equally sized grid areas (906a, 906b).

8. The encoder as claimed in any of the previous claims, wherein the means for associating is configured to associate a frame subdivision number indication (tmp) with each frame which has the second (FIXFIX) of the at least two possible reconstruction modes associated with it, the means for generating being configured such that the grid boundaries within these frames subdivide these frames into a number of grid areas, said number depending on the respective frame subdivision number indication.

9. The encoder as claimed in any of the previous claims, wherein the means for generating is configured such that the frame boundaries of the frames always coincide with grid boundaries of the grid independently of the possible reconstruction modes associated with the frames.

10. The encoder as claimed in any of the previous claims, wherein the means for generating comprises an analysis filter bank (110) which generates a set of spectral values (250) for each filter bank time slot (904) of the information signal, each frame (902) having a length of several filter bank time slots, and the means (112) for generating further comprising a means for averaging the energy spectral values in the resolution of the grid.

11. The encoder as claimed in claim 10, wherein the transient position indication is defined in units of the filter bank time slots (904).

12. The encoder as claimed in any of the previous claims, wherein the information signal is an audio signal.

13. A decoder comprising

a means (306) for extracting, from the encoded information signal, an encoded low-frequency portion of an information signal, a representation of a spectral envelope of a high-frequency portion of the information signal, information on reconstruction modes associated with frames of the information signal and corresponding with one, respectively, of at least two reconstruction modes, and transient position indications associated with frames, in each case, which have a first one of the at least two reconstruction modes associated with them;

a means (308) for decoding the encoded low-frequency portion of the information signal in units of frames of the information signal;

a means (310) for providing a preliminary high-frequency portion signal on the basis of the decoded low-frequency portion; and

a means (318, 312, 314) for spectrally adapting the preliminary high-frequency portion signal to the spectral envelopes by means of spectral weighting of the preliminary high-frequency portion signal as a function of the representation of the spectral envelopes in a temporal grid which depends on the reconstruction modes associated with the frames, such that for frames having the first one of the at least two possible reconstruction modes associated with them, the frame boundaries of these frames coincide with grid boundaries of the grid, and the grid boundaries of the grid within these frames depend on the transient position indication.

14. The decoder as claimed in claim 13, wherein the means for spectrally adapting is configured such that the grid boundary, or grid boundaries, within a frame having the first one of the at least two possible reconstruction modes associated with it is/are located such that it/they specify/specifies at least a first grid area (220) whose position within the respective frame depends on the transient position indication, and whose temporal extension is smaller than ⅓

of a length of the frames, as well as a second and/or third grid area(s) (222a, 222b) which take(s) up the remaining part of the respective frame from the first grid area up to the frame boundary, which is leading in terms of time, or trailing in terms of time (902a, 902b), of the respective frame.

15. The decoder as claimed in claim 14, wherein the means for extracting is configured to expect one or several spectral envelope values in the encoded information signal, and to extract same from the encoded information signal, only for the first and third grid areas (412, 414), for a frame (404) having the first reconstruction mode associated with it which comprises three grid areas (410, 412, 414) and wherein the first grid area (412) among the three grid areas is more to a preceding frame (406) than a predetermined value, said one or several spectral envelope values describing the spectral envelope with a respective frequency resolution, and to obtain, for the second grid area (410), one or several spectral envelope values for the representation of the spectral envelope from the grid area (408), which is the last in terms of time, of the preceding frame (406).

16. The decoder as claimed in claims 14 or 15, wherein the means for extracting is configured to expect one or several spectral envelope values in the encoded information signal, and to extract same from the encoded information signal, for both grid areas, for a frame (502) having the first reconstruction mode associated with it which comprises two grid areas (502a, 502b) and wherein the first grid area (502b) borders on the frame boundary, trailing in terms of time, of the frame (502), said one or several spectral envelope values describing the spectral envelope with a respective frequency solution, and to obtain from the spectral envelope value(s) for the first grid area (502b) one or several spectral envelope value(s) for a supplemental grid area (504b′

) in the subsequent frame (504), said supplementary grid area (504b′

) bordering on the trailing frame boundary, and to shorten accordingly a grid area (504a′

), leading in terms of time, of the subsequent frame (504), as is defined by the reconstruction mode of the subsequent frame, so as to start only at the supplementary grid area (504b′

), whereby the temporal grid within the subsequent frame (504) is subdivided, the means for spectral adaptation being configured to perform the adaptation in the subdivided temporal grid.

17. The decoder as claimed in claims 15 or 16, wherein the means for extracting is configured to introduce one or several spectral envelope values into the encoded information signal, or to extract same from the encoded information signal, for a frame having the second reconstruction mode associated with it or having the first reconstruction mode associated with it, but for which neither the condition that it comprises three grid areas and that, at the same time, the first grid area among the three grid areas is located closer to the preceding frame than the predetermined value, nor the condition that it comprises only two grid areas and that, at the same time, the first grid area borders on the frame boundary which is trailing in terms of time, are fulfilled, for each grid area of this frame.

18. The decoder as claimed in claim 17, wherein the means for spectrally adapting is configured such that the first grid area (220) borders on the frame boundary (902a), leading in terms of time, of the respective frame if there is no second grid area (222a), and wherein the first grid area (220) borders on the frame boundary (902b), trailing in terms of time, of the respective frame if no third grid area (222b) exists.

19. The decoder as claimed in any of claims 13 to 18, wherein the means for spectrally adapting is configured such that the grid boundaries within frames which have the second of the at least two possible reconstruction modes associated with them are located such that they are equally distributed over time, so that these frames only comprise one grid area or are subdivided into equally sized grid areas (906a, 906b).

20. The decoder as claimed in any of claims 13 to 19, wherein the means for extracting is configured to extract, from the encoded information signal, also a frame subdivision number indication which is associated, in each case, with frames which have the second of the possible reconstruction modes associated with them, the means for spectrally adaptating being configured such that the grid boundaries within these frames are subdivided into a number of grid areas, said number depending on the respective frame subdivision number indication.

21. The decoder as claimed in any of claims 13 to 20, wherein the means for spectrally adapting is configured such that the frame boundaries of the frames always coincide with grid boundaries of the grid independently of the possible reconstruction modes associated with the frames.

22. The decoder as claimed in any of claims 13 to 21, wherein the means for spectrally adapting comprises an analysis filter bank (310) which generates a set of spectral values for each filter bank time slot of the information signal, each frame having a length of several filter bank time slots, and the means for spectrally adapting further comprising a means (318) for determining the energy of the spectral values in the resolution of the grid.

23. The decoder as claimed in claim 22, wherein the transient position indication is defined in units of the filter bank time slots.

24. The decoder as claimed in any of claims 13 to 23, wherein the information signal is an audio signal.

25. An encoded information signal comprising

an encoded low-frequency portion of an information signal;

a representation of a spectral envelope of a high-frequency portion of an information signal; and

of information on reconstruction modes which are associated with frames of the information signal and each correspond to one of at least two reconstruction modes, and transient position indications each associated with frames which have a first one of the at least two reconstruction modes associated with them,

such that the information signal may be obtained from the encoded information signal by the following steps;

decoding the encoded low-frequency portion of the information signal in units of frames of the information signal;

providing a preliminary high-frequency portion signal on the basis of the decoded low-frequency portion; and

spectrally adapting the preliminary high-frequency portion signal to the spectral envelopes by spectrally weighting the preliminary high-frequency portion signal as a function of the representation of the spectral envelopes in a temporal grid which depends on the reconstruction modes associated with the frames, such that for frames which have the first one of the at least two possible reconstruction modes associated with them, the frame boundaries of these frames coincide with grid boundaries of the grid, and the grid boundaries of the grid within these frames depend on the transient position indication.

26. A method of encoding, comprising:

encoding a low-frequency portion of an information signal in units of frames (902) of the information signal;

localizing transients within the information signal;

associating, as a function of the localization, a

respective reconstruction mode from among at least two possible reconstruction modes (FIXFIX, LD_TRAN) with the frames of the information signal, and, for frames which have associated therewith a first one (LD_TRAN) of the at least two possible reconstruction modes, associating a respective transient position indication (bs_transient_position) with these frames; and

generating a representation of a spectral envelope of a high-frequency portion of the information signal in a temporal grid which depends on the reconstruction modes associated with the frames, such that frames which have the first one of the at least two possible reconstruction modes associated therewith, the frame boundaries (902a, 902b) of these frames (902) coincide with grid boundaries of the grid (222a, 220, 222b), and the grid boundaries of the grid within these frames depend on the transient position indication (T); and

combining the encoded low-frequency portion, the representation of the spectral envelope and information on the associated reconstruction modes and the transient position indications into an encoded information signal.

42. A computer program comprising a program code for performing the method as claimed in any of claims 26, 27, 33, 35, 39 and 40, when the computer program runs on a computer.

27. A method of decoding, comprising:

extracting, from the encoded information signal, an encoded low-frequency portion of an information signal, a representation of a spectral envelope of a high-frequency portion of the information signal and information on reconstruction modes associated with frames of the information signal and corresponding with one, respectively, of at least two reconstruction modes, and transient position indications associated with frames, in each case, which have a first one of the at least two reconstruction modes associated with them;

decoding the encoded low-frequency portion of the information signal in units of frames of the information signal;

providing a preliminary high-frequency portion signal on the basis of the decoded low-frequency portion; and

spectrally adapting the preliminary high-frequency portion signal to the spectral envelopes by means of spectral weighting of the preliminary high-frequency portion signal as a function of the representation of the spectral envelopes in a temporal grid which depends on the reconstruction modes associated with the frames, such that for frames having the first one of the at least two possible reconstruction modes associated with them, the frame boundaries of these frames coincide with grid boundaries of the grid, and the grid boundaries of the grid within these frames depend on the transient position indication.

28. A decoder comprising

a means (306) for extracting, from an encoded information signal, an encoded low-frequency portion of an information signal, information specifying a temporal grid (802a, 802b, 804a) such that at least one grid area (802b) extends across a frame boundary of two adjacent frames (802, 804) of the information signal so as to overlap with the two adjacent frames, and a representation of a spectral envelope of a high-frequency portion of the information signal;

a means (308) for decoding the encoded low-frequency portion of the information signal in units of the frames (802, 804) of the information signal;

a means (310) for determining a preliminary high-frequency portion signal on the basis of the decoded low-frequency portion; and

a means (318, 312, 314) for spectrally adapting the preliminary high-frequency portion signal to the spectral envelopes by means of spectrally weighting the preliminary high-frequency portion signal by means of deriving, from the representation of the spectral envelopes in the temporal grid (802a, 802b, 804a), a representation of the spectral envelopes in a subdivided temporal grid (802a, 802b₁, 802b₂, 804a), wherein the grid area (802b) overlapping with the two adjacent frames is subdivided into a first partial grid area (802b₁) and a second partial grid area (802b₂), which border on one another at the frame boundary, and by means of performing the adaptation of the preliminary high-frequency portion signal to the spectral envelopes by spectrally weighting the preliminary high-frequency portion signal in the subdivided temporal grid.

29. The decoder as claimed in claim 28, wherein the means for extracting is configured to extract, from the encoded information signal, information on reconstruction modes associated with the frames of the information signal, as the information specifying the temporal grid, the reconstruction modes, in each case, specifying grid areas of the temporal grid and corresponding to one of a plurality of possible reconstruction modes (FIXFIX, VARFIX, FIXVAR, VARVAR) respectively, and the means for extracting being configured to extract, from the encoded information signal, also an indication, for frames having a predetermined one (VARFIX, FIXVAR, VARVAR) of the possible reconstruction modes associated with them, which indicates how an outer grid boundary of an outer grid area (802b) of the frame (802) which overlaps with the frame (802) is to be aligned, in terms of time, with a frame boundary of the frame, and to extract, from the encoded information signal, one or several spectral envelope values for each grid area (802a,b,c) of the temporal grid.

30. The decoder as claimed in claim 29, wherein the means for spectrally adapting is configured to obtain, from the one or several spectral envelope values of the grid area (802b) overlapping with the two adjacent frames (802, 804), a first or several first spectral envelope values for the first partial grid area (802b₁) and a second or several second spectral envelope values for the second partial grid area (802b₂).

31. The decoder as claimed in claim 30, wherein the means for spectrally adapting is configured such that each spectral envelope value of the grid area (802b) overlapping with the two adjacent frames (802, 804) is divided into first and second spectral envelope values, respectively, as a function of a ratio of a size of the first partial grid area (802b₁) and a size of the second partial grid area (802b₂).

32. The decoder as claimed in any of claims 28 to 31, wherein the means for spectrally adapting comprises an analysis filter bank generating a set of spectral values per filter bank slot of the decoded information signal, each frame having a length of several filter bank time slots, and the means for spectrally adapting comprising a means for determining an energy of the spectral values in the resolution of the subdivided temporal grid.

33. A method of decoding, comprising:

extracting, from an encoded information signal, an encoded low-frequency portion of an information signal, information specifying a temporal grid (802a, 802b, 804a) such that at least one grid area (802b) extends across a frame boundary of two adjacent frames (802, 804) of the information signal so as to overlap with the two adjacent frames, and a representation of a spectral envelope of a high-frequency portion of the information signal;

decoding the encoded low-frequency portion of the information signal in units of the frames (802, 804) of the information signal;

determining a preliminary high-frequency portion signal on the basis of the decoded low-frequency portion; and

spectrally adapting the preliminary high-frequency portion signal to the spectral envelopes by means of spectrally weighting the preliminary high-frequency portion signal by means of deriving, from the representation of the spectral envelopes in the temporal grid (802a, 802b, 804a), a representation of the spectral envelopes in a subdivided temporal grid (802a, 802b₁, 802b₂, 804a), wherein the grid area (802b) overlapping with the two adjacent frames is subdivided into a first partial grid area (802b₁) and a second partial grid area (802b₂), which border on one another at the frame boundary, and by means of performing the adaptation of the preliminary high-frequency portion signal to the spectral envelopes by spectrally weighting the preliminary high-frequency portion signal in the subdivided temporal grid.

34. An encoder comprising:

a means (104, 106) for encoding a low-frequency portion of an information signal in units of frames (902) of the information signal;

a means (118, 116) for specifying a temporal grid (802a, 802b, 804a) such that at least one grid area (802b) extends across a frame boundary of two adjacent frames (802, 804) of the information signal so as to overlap with the two adjacent frames; and

a means (110, 112, 114) for generating a representation of a spectral envelope of a high-frequency portion of the information signal in the temporal grid; and

a means (108) for combining the encoded low-frequency portion, the representation of the spectral envelope and information on the temporal grid into an encoded information signal;

the means for generating and the means for combining being configured such that the representation of the spectral envelope in the grid area extending across the frame boundary of the two adjacent frames (802, 804) of the information signal depends on a ratio of a portion (802b₁) of this grid area which overlaps with one of the two adjacent frames, and of a portion of this grid area which overlaps with the other of the two adjacent frames (802b₂).

35. A method of encoding, comprising

encoding a low-frequency portion of an information signal in units of frames (902) of the information signal;

specifying a temporal grid (802a, 802b, 804a) such that at least one grid area (802b) extends across a frame boundary of two adjacent frames (802, 804) of the information signal so as to overlap with the two adjacent frames; and

generating a representation of a spectral envelope of a high-frequency portion of the information signal in the temporal grid; and

combining the encoded low-frequency portion, the representation of the spectral envelope and information on the temporal grid into an encoded information signal;

the step of generating and the step of combining being performed such that the representation of the spectral envelope in the grid area extending across the frame boundary of the two adjacent frames (802, 804) of the information signal depends on a ratio of a portion (802b₁) of this grid area which overlaps with one of the two adjacent frames, and of a portion of this grid area which overlaps with the other of the two adjacent frames (802b₂).

36. An encoder comprising

a means (104, 106) for encoding a low-frequency portion of an information signal in units of frames (902) of the information signal;

a means (118) for localizing transients within the information signal;

a means (116) for, as a function of the localization, associating a respective reconstruction mode from among at least two possible reconstruction modes with the frames of the information signal, and, for frames which have associated therewith a first one (FIXFIX) of the plurality of reconstruction modes, associating a respective absence indication with these frames; and

a means (110, 112, 114) for generating a representation of a spectral envelope of a high-frequency portion of the information signal in a temporal grid which depends on reconstruction modes associated with the frames, such that frames which have the first one of the plurality of possible reconstruction modes associated therewith, the frame boundaries (902a, 902b) of these frames (902) coincide with grid boundaries of the grid (222a, 220, 222b); and

a means (108) for combining the encoded low-frequency portion, the representation of the spectral envelope and information on the associated reconstruction modes and the transient absence indication into an encoded information signal,

the means for generating and the means for combining being configured to introduce, for a frame (404) having the first reconstruction mode associated with it, either no or one or several spectral envelope value(s) describing the spectral envelope with a respective frequency resolution, as part of the representation of the spectral envelope, into the encoded information signal for the first, in terms of time, grid area of this frame as a function of the transient absence indication.

37. The encoder as claimed in claim 36, wherein the means for generating is configured such that the grid boundaries within frames which have the second (FIXFIX) of the at least two possible reconstruction modes associated with them are located such that they are equally distributed over time, so that these frames only comprise one grid area or are subdivided into equally sized grid areas (906a, 906b).

38. A decoder comprising

a means (306) for extracting, from the encoded information signal, an encoded low-frequency portion of an information signal, a representation of a spectral envelope of a high-frequency portion of the information signal, information on reconstruction modes associated with frames of the information signal and corresponding with one, respectively, of a plurality of reconstruction modes, and transient absence indications associated with frames, in each case, which have a first one of the plurality of reconstruction modes associated with them;

a means (308) for decoding the encoded low-frequency portion of the information signal in units of the frames (802, 804) of the information signal;

a means (310) for determining a preliminary high-frequency portion signal on the basis of the decoded low-frequency portion; and

a means (318, 312, 314) for spectrally adapting the preliminary high-frequency portion signal to the spectral envelopes by means of spectral weighting of the preliminary high-frequency portion signal in a temporal grid which depends on the reconstruction modes associated with the frames, such that frames having the first one of the plurality of possible reconstruction modes associated with them, the frame boundaries (902a, 902b) of these frames (902) coincide with grid boundaries of the grid (222a, 220, 222b), and the means for spectrally adapting utilizes one or several spectral envelope values per grid area within these frames for representing the spectral envelopes, the means for extracting being configured to extract, for a frame (404) having the first reconstruction mode associated with it, for the first, in terms of time, grid area of this frame, as a function of the transient absence indication, either one or several spectral envelope values describing the spectral envelope with a respective frequency solution as part of the representation of the spectral envelope from the encoded information signal, or to obtain same from one or several spectral envelope values of a grid area, which is adjacent to the first, in terms of time, grid area, of the frame leading in terms of time.

39. A method of encoding, comprising

encoding a low-frequency portion of an information signal in units of frames (902) of the information signal;

localizing transients within the information signal;

associating, as a function of the localization, a respective reconstruction mode from among a plurality of possible reconstruction modes with the frames of the information signal, and, for frames which have associated therewith a first one (FIXFIX) of the plurality of reconstruction modes, associating a respective transient absence indication with these frames;

generating a representation of a spectral envelope of a high-frequency portion of the information signal in a temporal grid which depends on reconstruction modes associated with the frames, such that frames which have the first one of the plurality of possible reconstruction modes associated therewith, the frame boundaries (902a, 902b) of these frames (902) coincide with grid boundaries of the grid (222a, 220, 222b); and

combining the encoded low-frequency portion, the representation of the spectral envelope and information on the associated reconstruction modes and the transient absence indication into an encoded information signal,

the generating and combining being performed such that, for a frame (404) having the first reconstruction mode associated with it, either no or one or several spectral envelope value(s) describing the spectral envelope with a respective frequency resolution is/are introduced, as part of the representation of the spectral envelope, into the encoded information signal for the first, in terms of time, grid area of this frame as a function of the transient absence indication.

40. A method of decoding, comprising

extracting, from the encoded information signal, an encoded low-frequency portion of an information signal, a representation of a spectral envelope of a high-frequency portion of the information signal, information on reconstruction modes associated with frames of the information signal and corresponding with one, respectively, of a plurality of reconstruction modes, and transient absence indications associated with frames, in each case, which have a first one of the plurality of reconstruction modes associated with them;

decoding the encoded low-frequency portion of the information signal in units of the frames (802, 804) of the information signal;

determining a preliminary high-frequency portion signal on the basis of the decoded low-frequency portion; and

spectrally adapting the preliminary high-frequency portion signal to the spectral envelopes by means of spectral weighting of the preliminary high-frequency portion signal in a temporal grid which depends on the reconstruction modes associated with the frames, such that frames having the first one of the plurality of possible reconstruction modes associated with them, the frame boundaries (902a, 902b) of these frames (902) coincide with grid boundaries of the grid (222a, 220, 222b), and the means for spectrally adapting utilizes one or several spectral envelope values per grid area within these frames for representing the spectral envelopes,

the extracting being performed such that, for a frame (404) having the first reconstruction mode associated with it, for the first, in terms of time, grid area of this frame, as a function of the transient absence indication, either one or several spectral envelope values describing the spectral envelope with a respective frequency solution is extracted as part of the representation of the spectral envelope from the encoded information signal, or that same is obtained from one or several spectral envelope values of a grid area, which is adjacent to the first, in terms of time, grid area, of the frame leading in terms of time.

41. An encoded information signal comprising

an encoded low-frequency portion of an information signal;

a representation of a spectral envelope of a high-frequency portion of the information signal;

information on reconstruction modes associated with frames of the information signal and corresponding with one, respectively, of a plurality of reconstruction modes, and transient absence indications associated with frames, in each case, which have a first one of the plurality of reconstruction modes associated with them,

such that the information signal may be obtained from the encoded information signal by the following steps;

decoding the encoded low-frequency portion of the information signal in units of the frames (802, 804) of the information signal;

determining a preliminary high-frequency portion signal on the basis of the decoded low-frequency portion; and

spectrally adapting the preliminary high-frequency portion signal to the spectral envelopes by means of spectral weighting of the preliminary high-frequency portion signal in a temporal grid which depends on the reconstruction modes associated with the frames, such that frames having the first one of the plurality of possible reconstruction modes associated with them, the frame boundaries (902a, 902b) of these frames (902) coincide with grid boundaries of the grid (222a, 220, 222b), and the means for spectrally adapting utilizes one or several spectral envelope values per grid area within these frames for representing the spectral envelopes,

the extracting being performed such that extract, for a frame (404) having the first reconstruction mode associated with it, for the first, in terms of time, grid area of this frame, as a function of the transient absence indication, either one or several spectral envelope values describing the spectral envelope with a respective frequency solution is extracted as part of the representation of the spectral envelope from the encoded information signal, or that same is obtained from one or several spectral envelope values of a grid area, which is adjacent to the first, in terms of time, grid area, of the frame leading in terms of time.