Section 24: Connection Setup
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T E C H N O L O G Y
Page 219
24.9.1.
What’s the difference between MPEG-1, MPEG-2, MPEG-3 &
MPEG-4?
The differences between MPEG 1, 2, 3, and 4 have resulted from
evolutionary advances in audio coding over the past decade or so. Each
subsequent set of MPEG standards has provided greater compression
efficiency and more options for coding not only audio, but video as well.
In the following sections we will give a brief overview of MPEG audio. If you
require more detailed information on MPEG audio it can be sourced from
http://www.chiariglione.org/mpeg/
24.9.1.1.
MPEG-1
This was the first set of MPEG standards produced and it has three
operation modes or ‘layers’. These are:
Layer-1: The compression used in Digital Compact Cassettes;
Layer-2 (MP2): The MUSICAM
®
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compression format used in
CDs and Video CDs ; and
Layer-3 (MP3): the MP3 compression format used widely to rip
tracks from CDs for portable digital music players.
MPEG-1 layers can provide single channel, dual channel, stereo and joint
stereo coding and all of these operating modes are supported in
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codecs. Each ‘layer’ has improved upon the previous one by performing
better at lower bitrates.
The sampling frequencies available for MPEG-1 include 32kHz, 44.1kHz
and 48kHz.
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codecs support 32kHz and 48kHz sampling
frequencies for MPEG-1 algorithms.
MPEG 1 Layer 2 (
MP2)
and Layer 3
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(
MP3
) are included in
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codecs.
24.9.1.2.
MPEG-2
MPEG-2 standards followed the MPEG-1 standards and were designed to
be the successor to the popular MP3 format. The standards included the
attributes of MPEG-1 as well as:
Backwards compatibility with MPEG-1;
Surround sound 5.1 capability (please note that MP3 surround has
since become available); and
Coding at the lower sampling frequencies (LSF) of 16 kHz, 22.05
kHz and 24kHz using Layer-1, Layer-2 and Layer-3.
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Musicam is a registered trademark of Musicam USA.
21
Please check with
T
ieline
at [email protected] for the implementation date of this
feature.
