Methods for improving high frequency reconstruction

Decoder for decoding an encoded signal, the encoded signal including an encoded input signal representing a frequency content of an original audio signal below a predetermined frequency, and an additional information, the decoder comprising:

• a coding algorithm for decoding the encoded input signal to produce a decoded input signal;
• a reconstructor for reconstruction differences between the original audio signal and a regenerated signal based on the additional information;
• a high frequency generator for performing a high frequency regeneration technique to obtain the regenerated signal;
• a producer for producing a high frequency regenerated audio signal based on the decoded input signal, the reconstructed differences and the regenerated signal, wherein the reconstructor is arranged for determining a certain scale factor band ls into which a synthetic sine is to be inserted, and
• wherein a level of a synthetic sine to be inserted is defined as follows:
• gsine(n)=√{square root over ( e(n))}
• wherein n is a number of the given scale factor band, and e is the spectral envelope vector, and
• wherein the producer is arranged for determining a band pass signal for the channel in which the synthetic sine is to be placed in accordance with the following equation:
• yre(ls)=xre(ls)·ghfr(ls)+gsin(ls)· φre(k)
• yim(ls)=xim(ls)·ghfr(ls)+gsin(ls)·(−1)ls· φim(k)
• wherein ls is a filter bank channel number, into which a sine is to be inserted, wherein ll is the lowest filter bank channel number for the scale factor band, wherein lu is the highest filter bank channel for the scale factor band, wherein xre is the real part of a band pass signal sample output by the HFR block, wherein xim is an imaginary part of the band pass signal sample output by the HFR block, and wherein yre and yim are the real part and the imaginary part of an adjusted band pass signal for a filter bank channel, and wherein ghfr is a gain adjustment factor derived from the noise-floor level vector,
• wherein φre and φim form a complex modulation vector for placing a sine into a band pass signal and wherein k is a modulation vector index ranging between 0 and 4.