Effectiveness of MPEG audio
MPEG Audio Compression
MPEG defines 3 layers for audio. Basic model is same, but codec complexity increases with each layer.
Divides data into frames, each of them contains 384 samples, 12 samples from each of the 32 filtered subbands as shown below.
Figure: Grouping of Sub-band Samples for Layer 1, 2, and 3
Layer 1: DCT type filter with one frame and equal frequency spread per band. Psychoacoustic model only uses frequency masking.
Layer 2: Use three frames in filter (before, current, next, a total of 1152 samples). This models a little bit of the temporal masking.
Layer 3: Better critical band filter is used (non-equal frequencies), psychoacoustic model includes temporal masking effects, takes into account stereo redundancy, and uses Huffman coder.