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Figure 12 | EURASIP Journal on Audio, Speech, and Music Processing

Figure 12

From: An Overview of the Coding Standard MPEG-4 Audio Amendments 1 and 2: HE-AAC, SSC, and HE-AAC v2

Figure 12

Envelope 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.

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