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Digital audio terms
AAC
Advanced Audio Coding (AAC) is one of the audio compression formats defined by the
MPEG-2 specification. AAC used to be called NBC (Non-Backward-Compatible), because it
is not compatible with the MPEG-1 audio formats. AAC may eventually replace MP3 since it
offers better sound quality and greater file compression.
ADPCM
Adaptive Differential Pulse Code Modulation (ADPCM), is a form of pulse code modulation
(PCM) that produces a digital audio signal with a lower bit rate than standard PCM. The Rio
800 uses ADPCM for voice recording. ADPCM produces a lower bit rate by recording only
the difference between samples, and adjusting the coding scale dynamically to accommo-
date large and small differences.
Bitrate
Bitrate denotes the number of bits per second used to represent a digital music file. The size
and quality of a compressed digital audio file is determined by the bitrate used when encod-
ing the file. The higher the bitrate used, the higher the sound quality, and the larger the file
size. For example, with MP3, a bitrate of 128kbps (128,000 bits per second) is generally
thought of as "CD quality", and takes up about 1 megabyte (MB) per minute of music. At a
64kbps bitrate, the sound quality is similar to that of an FM radio signal, but you can get
around two minutes of music in that same 1MB of storage space. CD audio has a bitrate of
1.4Mbits per second (1,400,000 bits/second).
Codec
Depending on the context and kind of technology involved, codec can be defined as a com-
pressed digital audio file format (like MP3, WMA, and so on), a "coding/decoding" chip used
to translate between digital and analog transmissions (used in modems), or a compression/
decompression algorithm. Codecs compress audio data into a file, often for efficient transmis-
sion over a network, and then decode it for playback. While all the codecs perform similar
compression of digital audio, there are differences in the technology.
The Rio 800 supports the following digital audio codecs:
•
MP3.
•
WMA.
•
ADPCM—for voice recording
•
ACELP.net (Audible)
DRM, security
Digital Rights Management (DRM) technologies protect copyright ownership of digital infor-
mation. DRM became an issue with the rise of MP3 technology and Internet distribution of
music. DRM platforms serve as a security "wrapper" around digital audio supporting Internet
distribution while at the same time protecting and managing rights related to that digital infor-
mation.
Digital audio terms
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