White Paper
M600
36
February 2006
Media formats
Audio formats
Format
Description
AAC-LC
Advanced Audio Coding. AAC is the latest audio coding standard, defined in the
MPEG-2 standard and is used for high-quality audio compression. AAC provides higher
quality than MP3 at the same bit rate, or for the same audio quality it uses a 30 per cent
lower bit rate. It supports the coding of multichannel audio, with up to 48 main chan-
nels and 16 low-frequency channels. The AAC offers three different profiles to facilitate
trade off between quality, memory and processing power requirements. They include:
Main Profile (MP), Low Complexity (LC) and Scalable Sampling Rate (SSR). The Media
player can play AAC-LC format audio which is encoded into an MPEG-4 file or stream.
The Sound recorder use the AAC-LC format for recording.
AMR-NB
Adaptive Multi Rate. AMR-NB is a speech compression format that is highly optimized
for the mobile environment, requiring as little as 4.75 Kbps bandwidth. AMR-NB is used
to convey voice recordings in MMS, 3GPP video clips or streams. M600 records AMR
using 12.2 Kbps with a sample rate of 8 kHz.
AU
Similar to WAV, this is an audio format commonly used in the Macintosh, Unix and
Java™ worlds. It is not commonly used for content on mobile devices.
iMelody
A format commonly used for monophonic ringtones. (M600 ringtones can use up to 40
voices.)
MIDI
Musical Instrument Digital Interface.
MIDI is not a recording of music, but a description which enables a local synthesizer to
play the music from the instructions included in the MIDI file. Since a MIDI file only rep-
resents player information, it is far more concise than formats that store the sound
directly. An advantage is very small file sizes. A disadvantage is the lack of specific
sound control. MIDI is ideal for polyphonic ringtones. (M600 ringtones can use up to 40
voices.)
SP-MIDI
SP-MIDI stands for Scalable Polyphony MIDI. SP-MIDI is based on the MIDI format and
adapted for mobile phones and other portable products. The objective is to secure
interoperability between products with different sound capabilities.
Initial recommendations for using SP-MIDI in 3GPP™ applications are discussed in a
separate document,
Scalable Polyphony MIDI Device 5-24 Note Profile for
3GPP™
.
MP3
MP3 is the file extension for MPEG audio layer 3. Layer 3 is one of three coding
schemes (layer 1, layer 2 and layer 3) for the compression of audio signals. Layer 3
uses a very efficient compression method, removing all irrelevant parts of a sound sig-
nal that the human ear cannot perceive. The result is, CD digital audio (CDDA) is con-
verted to MP3 with almost
untouched quality, compressed by a factor of around 12.
The high compression of audio in MP3 files makes them relatively small, though MP3
files can be created with different size and quality compromises. The small file size,
together with the excellent sound quality, are the main reasons for the MP3-format’s
massive popularity when sharing music over the Internet.
RMF
Rich Music Format
TM
. A file format developed by Beatnik combining the compact size
of MIDI files with the high quality of sampled sound.
