| A thru H |
Definition of Terms 
|
| A2b |
A2b music an online music delivery company owned by AT&T. The service
delivers music coded in a proprietary format based on MPEG-2
AAC. The format includes copyright protection technology. |
| Download Audio |
Downloading, which involves transferring the entire file to your computer
before any part of it is accessible, offers better quality since the data
rate of the compressed stream does not have to less than the data rate
of the internet connection. MP3 audio for example, is
targeted at data rates from 64 to 128 Kbps. The goal of these formats is
to provide near CD quality audio. |
| G2 |
G2 is the name of the RealNetworks most
recent audio/video CODEC technology. The G2 includes several features targeted
specifically at streaming media applications including synchronization
with other media types such as video and graphics, and the ability to handle
data loss. According to RealAudio, the G2 Music Codec can handle packet
loss up to 10-15% with minimal reduction of audio quality. |
| I thru P |
|
| Liquid Audio |
Based in Redwood City, Liquid Audio is the pioneer and current market
leader in downloadable media commerce technology on the Internet. The company
derives its revenue from the delivery of software products including authoring
tools, and servers for media commerce; as well as media commerce services.
While the Liquid Audio media architecture can support multiple audio coding
standards, the default codec is based on AAC and
includes copy protection features. |
MPEG
(Motion Picture Experts Group) |
MPEG is the name of a working group established under the joint direction
of the International Standards Organization/International Electrotechnical
Commission (ISO/IEC). The purpose of this working group is to create standards
for the digital video and the audio compression. |
| MPEG Stages |
The generations of standards defined by the MPEG
working group are referred to as stages. These stages are normally noted
in Arabic figures (MPEG-1, MPEG-2, and MPEG-4). |
| MPEG Audio Layers |
MPEG-1 and MPEG-2 both have a three-layer structure, each of which
represents a family of coding algorithms. These layers are noted in the
standards using Roman figures (Layer I, Layer II, and Layer III). Note
that for Internet audio applications MPEG-1 Layer III audio has become
known as MP3. |
MPEG-2 AAC
(Advanced Audio Coding) |
AAC (Advanced Audio Coding) is one of the audio compression formats
defined by the MPEG-2 standard. AAC used to be called NBC (Non-Backward-Compatible),
because it is not compatible with the MPEG-1 audio formats. MPEG-2 also
defined another audio format called MPEG-2 Multichannel or MPEG-2 BC (Backward
Compatible), which is compatible with MPEG-1. AAC is more efficient than
MP3 (MPEG-1 Layer III) and is the state of the art in audio compression
technology. Formal listening tests have demonstrate it is able to provide
slightly better audio quality at 96 kb/s than layer-3 at 128 kb/s or layer-2
at 192 kb/s. |
| MP3 |
MP3 (MPEG Layer III Audio Coding)
The MPEG Layer 3 audio compression scheme that was defined as part
of the International Standards Organization (ISO) Moving Picture Experts
Group (MPEG) audio/video coding standard. MPEG-I defined
three encoding schemes, referred to as Layer I, Layer II, and Layer III.
Each of these schemes uses increasing sophisticated encoding techniques
and gives correspondingly better audio quality at a given bit rate. The
three layers are hierarchical, in that a Layer III decoder can decode Layer
I, II, and III bitstreams; a Layer II decoder Layer II, and I bitstreams;
and a Layer I decoder only Layer I bitstreams. Each of the layers support
decoding audio sampled at 48, 44.1, or 32 kHz. MPEG 2 uses the same family
of codecs but extends it by adding support for 24, 22.05, or 16 kHz sampling
rates as well as more audio channels for surround sound and multilingual
applications. |
| Q thru Z |
|
| Qdesign Music Codec |
Based in British Columbia, Qdesign developed a high quality, streaming
audio CODEC. Distributed by Apple as part of their QuickTime media
architecture, this CODEC gives excellent quality at dialup data rates. |
| RealNetworks |
Based in Seattle, RealNetworks is the pioneer and current market leader
in streaming media technology on the Internet. According to the company,
their technology is used to deliver content on more than 85% of all streaming
media enabled Web pages. The company derives its revenue from the delivery
of software products including authoring tools, streaming media servers,
and players; as well as streaming media delivery services. |
| Streaming Audio |
Streaming refers to the playback of audio in real-time as it is transferred
across the Internet. The advantage of this approach is that the user does
not have wait for the entire music file to be downloaded before hearing
it. The tradeoff is that the music must be highly compressed in order to
support the access rates that most users have, typically 28.8 to 56 Kbps.
This gives Net users instant gratification but relatively poor playback
quality. In addition streaming audio players do not capture the content,
so each time the clip is played it is transferred again. |
TwinVQ
(Transform-domain Weighted Interleave Vector Quantization) |
This compression technology, targeted at download applications, was
originally developed by Yamaha and has been incorporated, along with AAC,
into the MPEG-4 specification. The underlying algorithms are significantly
different the algorithms used in MPEG layer III. |
| WMA (Windows Media Audio) |
Part of Microsoft’s Windows Media Technologies, which combines Video
for Windows, ActiveMovie, and NetShow into a unified architecture. A key
feature of this architecture is that it automatically downloads CODECs
for new formats from the Internet as needed. |
MP3
Overview