Image Processing Reference
In-Depth Information
K
Source-Audio Formats
K.1
Relevant Audio Formats
A selection of formats that you might encounter when processing and encoding audio is
enumerated in Table K-1.
K-1 A Variety of Audio Formats
Format
Description
µ
-Law
This is an old legacy codec for use in telephony applications.
The
-Law codec is widely available on UNIX-based systems.
It may be worth being able to decode this, but it has few
applications for an encoder nowadays.
µ
a-Law
A variant on the
-Law codec also used for telephony. The a-Law
codec is of little use now that we have better codecs available.
Being able to decode it may gain access to some legacy audio files.
µ
AAC format
Part of the MPEG-4 standard but has been superseded by
AAC
. This was originally developed as part of the MPEG-2
standard. The MPEG-4 implementations are somewhat extended.
At the same bit rate as MP3, the quality is far superior. At the
same subjective quality, AAC files are much smaller than MP3
files. Because it is another open standard it is already well
supported and will be more widely supported in the future.
Currently available via Apple iTunes and RealNetworks
Rhapsody, and used in 3G cell phones.
+
AAC
+
format
Also known as HE-AAC. This is an improved version of the
AAC format, likely to become a dominant format in the future.
This variant adds Spectral Band Replication. Running this at 128
bps delivers a stereo output that is claimed to be
indistinguishable from the original. AAC plus is being deployed
on XM Satellite Radio and used in 3G cell phones.
Continued
695
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