Databases Reference
In-Depth Information
Frame 1
Frame 2
Frame 3
Bit
allocation
Scale
factors
Subband
data
Header
CRC
F I GU R E 17 . 5
Frame structure for Layer 1.
T A B L E 17 . 1
Allowable sampling
frequencies in MPEG-1 and
MPEG-2.
Index
MPEG-1
MPEG-2
00
44.1kHz
22.05kHz
01
48kHz
24kHz
10
32kHz
16kHz
11
Reserved
together. The joint stereo mode consists of two channels that are encoded together. The left
and right channels are combined to form a
mid
and a
side
signal as follows:
L
+
R
M
=
2
L
−
R
S
=
2
The dual channel mode consists of two channels that are encoded separately and are not
intended to be played together, such as a translation channel. These are followed by two mode
extension bits that are used in the joint stereo mode. The next bit is a copyright bit (“1” if the
material is copyrighted, “0” if it is not). The next bit is set to “1” for original media and “0”
for copy. The final two bits indicate the type of de-emphasis to be used.
If the CRC bit is set, the header is followed by a 16-bit CRC. This is followed by the bit
allocations used by each subband and is in turn followed by the set of 6-bit scalefactors. The
scalefactor data is followed by the 384 quantized samples.
17.3.2 Layer II Coding
The Layer II coder provides a higher compression rate by making some relatively minor
modifications to the Layer I coding scheme. These modifications include how the samples are
