Through an iterative algorithm, the bit allocation uses
information from the psychoacoustic model to determine the number of code bits to be
allocated to each subband. This process can be described using the following formula:
MNRdB = SNRdB - SMRdB
||MNRdB is the mask-to-noise ratio
||SNRdB is the signal-to-noise ratio, given with the MPEG
audio standard in a table
||SMRdB is the signal-to-mask ratio, derived from the
Then the subbands are placed in order of lowest to highest mask-to-noise ratio, and the
lowest subband is allocated the smallest number of code bits and this process continues
until no more code bits can be allocated (Pan 5).
Two nested iteration loops called the rate loop and the distortion loop serve to
quantize and code in MP3 encoders. The quantized values are coded using Huffman methods, which is lossless.