L64105 LSI Logic Corporation, L64105 Datasheet - Page 342

• Manufacturer Part Number: L64105
• Description: Mpeg-2 Audio/video Decoder
• Manufacturer: LSI Logic Corporation

10.4 MPEG Audio Decoder
10.4.1 MPEG Audio Syntax
10-10
The L64105 MPEG Decoder supports Layer I and Layer II of the
MPEG-1 audio compression and MPEG-2 low bit rate decoding. For
MPEG-2 multichannel audio streams, the L64105 decodes the left and
right channels and ignores the others.
The basic MPEG audio bitstream syntax is shown in
four bytes of frame header contain the 12-bit sync word and information
on the characteristics of the audio, such as audio layer, sample
frequency, bit rate, mode (mono, stereo, joint stereo, or dual channel),
copyright, etc. If the protection bit in the header is set, the header is
followed by a 2-byte CRC. In the Layer I stream, the CRC is for the audio
data up to the scale-factors boundary. Similarly, in Layer II, the CRC is
for the data up to the end of the scale-factor index.
The length of the scale factors is fixed at six bits. The encoded subband
samples can vary from 2 to 15 bits in length. The length of the samples
per subband is indicated by the four bits of allocation information for each
subband at the beginning of the data.
Layer I supports bit rates from 192 to 448 Kbits/sec. Layer II, which uses
a more complex encoding model, provides CD quality audio at
128 Kbits/sec/channel and performs better compression of stereo
signals. The highest supported bit rate for Layer II is 384 Kbits/s.
There are 384 PCM sample pairs encoded in each Layer I frame and
1152 PCM sample pairs in each Layer II frame. When a 48-kHz sampling
frequency is assumed, the decoding time is 8 ms for a Layer 1 frame and
24 ms for a Layer II frame.
The MPEG-2 audio compression standard is compatible with MPEG-1. It
provides a more sophisticated encoding scheme with low bit-rate support
and encodes up to five audio channels. The L64105 Audio Decoder
complies with the MPEG-2 low bit-rate standard and is able to decode a
wide range of audio bit rates from 8 to 448 Kbps. For MPEG-2
multichannel audio streams, the L64105 Audio Decoder processes only
the left and right channels.
Audio Decoder Module
Note:
“Free format” bit rate is not supported in the L64105
Decoder.
Figure
10.2. The