Even if the above methods can be interpreted as transforms, there are
coders which more explicitly use linear transforms, such as the FFT, DCT
(Discrete Cosine Transform), MDCT (Modified Cosine Transform) and so
on. Currently most used is the MDCT (see section 4.1.1), which
combines 50% overlap with ``critical subsampling''. Dolby's AC-3 uses
purely MDCT for coding, and MPEG-1 layer III and MPEG-2 AAC
use hybrid
subband-MDCT methods.