Digital Sound & Music: Concepts, Applications, & Science, Chapter 5, last updated 6/25/2013
62
Field Length in Bits Contents
A 11 all 1s to indicate start of frame
B 2 MPEG-1 indicated by bits 1 1
C 2 Layer III indicated by bits 0 1
D 1 0 means protected by CRC* (with 16 bit CRC
following header)
1 means not protected
E 4 bit rate index
0000 free
0001 32 kb/s
0010 40 kb/s
0011 48 kb/s
0100 56 kb/s
0101 64 kb/s
0110 80 kb/s
0111 96 kb/s
1000 112 kb/s
1001 128 kb/s
1010 160 kb/s
1011 192 kb/s
1100 224 kb/s
1101 256 kb/s
1110 320 kb/s
1111 bad
F 2 frequency index
00 44100 Hz
01 48000 Hz
10 32000 Hz
11 reserved
G 1 0 frame is not padded
1 frame is padded with an extra byte
Padding is used so that bit rates are fitted exactly to
frames. For example, a 44100 Hz audio signal at 128
kb/s yields a frame of about 417.97 bytes
H 1 private bit, used as desired by implementer
I 2 channel mode
00 stereo
01 joint stereo
10 2 independent mono channels
11 1 mono channel
J 2 mode extension used with joint stereo mode
K 1 0 if not copyrighted
1 if copyrighted
L 1 0 if copy of original media
1 if not
M 2 indicates emphasized frequencies
*CRC stands for cyclical redundancy check, an error correcting code that checks for
errors in the transmission of data.
Table 5.4 Contents of MP3 frame header
MP3 supports both constant bit rate (CBR) and variable bit rate (VBR). VBR makes
it possible to vary the bit rate frame-by-frame, allocating more bits to frames that require greater
Previous Page Next Page