User guide

Page 24

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 dif-

ference between samples and adjusting the coding scale dynamically to accommodate large

and small differences.

Bitrate

Bitrate 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 bitrate used when encoding 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 128k is usually very close to CD quality, and takes up about 1MB per

minute of music. At a 64k bitrate, the sound quality is similar to that of an FM radio signal, but

you may get around two minutes of music in that same 1MB of storage space.

CDDB

See Gracenote.

Codec

Depending on the context and 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 analog transmissions. A modem uses one to interpret incoming analog

signals and converts the digital data stream coming from the computer into analog. 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)