Iso/Mpeg Layer Ii - Telos Zephyr User Manual

ISO/MPEG LAYER II

MPEG Layer II is the world's most popular perceptual coding method. This is primarily
because it is less complex to implement than Layer III, particularly at the encoder. It is
the preferred choice for applications where greater than 120 kbps/channel is available,
such as satellite links and high- capacity terrestrial paths such as Primary ISDN or T1
channels.
We include it in the Zephyr in order to offer compatibility with the widest variety of
codec equipment.
Our implementation is the very highest quality, the critical DSP code having been
obtained and licensed directly from the primary inventor of LII, the IRT in Munich.
110
Section 7
32 Bands 576 Bands
Polyphase
MDCT
Filterbank
Filters
1024 point FFT/
Perceptual Model
Block diagram of the Layer III coding process.
CURIOSITY NOTE!
Layer III is the direct successor to the "ASPEC" algorithm
which was based on coding methods by Fraunhofer/University
of Erlangen, AT&T, Thomson Consumer Electronics, and
CNET (Centre National d'Edudes des Télécommunications).
In the first tests for ISO in 1990, ASPEC showed the best
sound quality, with an advantage at lower bit rates. The
precursor to the Layer II algorithm called MUSICAM, had the
advantage of a lower complexity. LIII came from a merging of
both systems: For easier transcoding, LIII adopted the LII
filterbank for the first stage, and the bitstream rate was
adjusted.
AUDIO CODING PRINCIPLES
Huffman
Non-uniform
Coding
Quantization
Distortion
Control
Side
Information
External Control