The purpose of the filter bank
is to divide the audio signal into 32 equal-width frequency subbands. Empirical evidence
has shown that the human ear has a limited resolution that can be expressed in terms of
critical bandwidths less than 100Hz and more than 4kHz. Within a critical bandwidth the
human ear blurs frequencies. Thus the filter bank creates equal-width frequency subbands
that correlate to the critical bandwidths in a method diagrammed in the following figure.
While Layer 1 and Layer 2 uses just a polyphase filterbank, an additional MDCT is used in Layer 3 compression.
Next step: Psychoacoustics