AN APPARATUS AND A METHOD FOR CALCULATING A NUMBER OF SPECTRAL ENVELOPES

摘要

An apparatus (100) calculates a number (102) of spectral envelopes (104) to be derived by a spectral band replication (SBR) encoder, wherein the SBR encoder is adapted to encode an audio signal (105) using a plurality of sample values within a predetermined number of subsequent time portions (110) in an SBR frame extending from an initial time (t0) to a final time (tn), the predetermined number of subsequent time portions (110) being arranged in a time sequence given by the audio signal (105). The apparatus (100) comprises a decision value calculator (120) for determining a decision value (125), the decision value (125) measuring a deviation in spectral energy distributions of a pair of neighboring time portions. The apparatus (100) further comprises a detector (130) for detecting a violation (135) of a threshold by the decision value (125) and a processor (140) for determining a first envelope border (145) between the pair of neighboring time portions when the violation (135) of the threshold is detected. The apparatus (100) further comprises a processor (150) for determining a second envelope border (155) between a different pair of neighboring time portions or at the initial time (t0) or at the final time (tn) for an envelope having the first envelope border (145) based on the violation (135) of the threshold for the other pair or based on a temporal position of the pair or the different pair in the SBR frame. The apparatus (100) further comprises a number processor (160) for establishing the number (102) of spectral envelopes (104) having the first envelope border (145) and the second envelope border (155).