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Main audio channels
All single channel elements or channel pair elements in one program.
Mapping
Conversion of an audio signal from time to frequency domain by subband
filtering and/or by MDCT.
Masking
A property of the human auditory system by which an audio signal cannot
be perceived in the presence of another audio signal.
Masking threshold
A function in frequency and time below which an audio signal cannot be
perceived by the human auditory system.
MDCT (Modified Discrete Cosine Transform)
A transform which has the property of time domain aliasing cancellation.
MP2
MP2 is an acronym for MPEG-1 audio layer 2. It is a music compression
scheme used in CD-V and DVD-video.
MP3
MP3 is an acronym for MPEG-1 or MPEG-2 audio layer 3. It needs more power
to encode than MP2.
MPEG (Moving Pictures Experts Group)
MPEG is a group of people that meet under ISO (the International Standards
Organization) to generate standards for digital video (sequences of images
in time) and audio compression. In particular, they define a compressed
bit stream, which implicitly defines a decompressor. However, the compression
algorithms are up to the individual manufacturers, and that is where proprietary
advantage is obtained within the scope of a publicly available international
standard. MPEG meets roughly four times a year for roughly a week each
time. In between meetings, a great deal of work is done by the members,
so it doesn't all happen at the meetings. The work is organized and planned
at the meetings.
MPEG itself is a nickname. The official name is: ISO/IEC JTC1 SC29 WG11.
ISO: International Organization for Standardization
IEC: International Electro-technical Commission
JTC1: Joint Technical Committee 1
SC29: Sub-committee 29
WG11: Work Group 11 (moving pictures with audio)
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 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,
MPEG-4, MPEG-7 and MPEG-21).
M/S stereo
A method of removing imaging artefacts as well as exploiting stereo irrelevance
or redundancy in stereophonic audio programmes based on coding the sum
and difference signal instead of the left and right channels. Two channels are
then encoded: the middle channel (computed by (l+r)/sqrt(2)) and the side channel
(computed by (l-r)/sqrt(2)). Bits are saved by allowing less bits for the side channel.
Multichannel
A combination of audio channels used to create a spatial sound field.
Multilingual
A presentation of dialogue in more than one language.
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