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# Long description

The figure shows three squares in a row, representing the key tools that have been instrumental in the advancement of the MPEG-4 AAC family of standards. From left to right, these are perceptual noise substitution (PNS), spectral band replication (SBR) and parametric stereo (PS).

Above the three squares is a row of four rectangles. From left to right, these are labelled MPEG-2 AAC-LC, MPEG-4 AAC-LC, MPEG-4 HE-AAC and MPEG-4 HE-AAC v2. Between each pair of rectangles is a short horizontal arrow pointing to the right, so three arrows in total.

The three squares are connected to the three arrows between the four rectangles. The connections are shown by three dashed vertical lines.