+ * @file
+ * Common code between the AC-3 and E-AC-3 decoders.
+ *
+ * Summary of MDCT Coefficient Grouping:
+ * The individual MDCT coefficient indices are often referred to in the
+ * (E-)AC-3 specification as frequency bins. These bins are grouped together
+ * into subbands of 12 coefficients each. The subbands are grouped together
+ * into bands as defined in the bitstream by the band structures, which
+ * determine the number of bands and the size of each band. The full spectrum
+ * of 256 frequency bins is divided into 1 DC bin + 21 subbands = 253 bins.
+ * This system of grouping coefficients is used for channel bandwidth, stereo
+ * rematrixing, channel coupling, enhanced coupling, and spectral extension.
+ *
+ * +-+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+-+
+ * |1| |12| | [12|12|12|12] | | | | | | | | | | | | |3|
+ * +-+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+-+
+ * ~~~ ~~~~ ~~~~~~~~~~~~~ ~~~
+ * | | | |
+ * | | | 3 unused frequency bins--+
+ * | | |
+ * | | +--1 band containing 4 subbands
+ * | |
+ * | +--1 subband of 12 frequency bins
+ * |
+ * +--DC frequency bin