Transform Coders

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 ¹ use hybrid subband-MDCT methods.