Operation Manual

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Digital audio terms
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 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 accommodate
large and small differences.
Bit Rate
Bit rate denotes the number of bits per second used to represent an audio signal. The size
and quality of a digital audio file is determined by the bit rate used when encoding the file.
The higher the bit rate used, the higher the sound quality and the larger the file size. For
example, with MP3, a bit rate of 128 k is usually very close to CD quality, and takes up about
1 MB per minute of music. At a 64 k bit rate, the sound quality is similar to that of an FM radio
signal, but you may get around two minutes of music in that same 1 MB of storage space.
CDDB
See Gracenote.
Codec
Depending on the context and the kind of technology involved, codec may be defined in two
ways. In telecommunications, a codec is usually a “coding/decoding” chip used to translate
between digital and analogue transmissions. A modem uses one to interpret incoming
analogue signals and converts the digital data stream coming from the computer into
analogue. A codec is also defined as a compression/decompression algorithm. Codecs are
used to compress audio data into a file, often for efficient transmission over a network, and
then decode it for playback.
The Rio 800 supports the following digital audio file codecs:
•MP3
•WMA
• ADPCM—for voice recording
• ACELP.net (Audible)