Figure 12From: An Overview of the Coding Standard MPEG-4 Audio Amendments 1 and 2: HE-AAC, SSC, and HE-AAC v2Envelope adjustment in a real-valued QMF filter bank. In the top panel, sinusoids are again displayed within QMF subbands. The second panel illustrates the signs calculated for the different subbands as a function of the reflection coefficients of the subbands. As is clear from the figure, a lower subband with sign 1 adjacent to a higher subband with sign −1 indicates that the two subbands have a shared sinusoid in the overlapping range. In the third panel, the modified gain vector is displayed. Here it is clear that the gain-values for the subbands that share a sinusoid in the overlapping range are identical. The lower panel illustrates the output after envelope adjustment, and as can be seen no aliasing is introduced due to the gain adjustment.Back to article page