Omnia Audio Omnia.9/XE - Manual (Page 105)

At a bit rate of 96 kbps stereo, the sample rate should be set to 32kHz with a Final Output Level of -1.0.
For bit rates of 64 kbps stereo and lower, we recommend changing the sample rate to 22.05kHz and
setting the Final Output Level to -2.0 to prevent any chance of decoder-side clipping.
If you need to provide a very low bit rate MP3 stream, we suggest using 32 kbps mono at a sample rate
of 22.05kHz with a Final Output Level of -2.0.
AAC
Technical Details
AAC - an abbreviation for Advanced Audio Coding - is a form of MPEG-4 encoding usually presented in
an MP4 wrapper and commonly (if not incorrectly) referred to as just “MP4”. It is the most modern “lossy”
encoder available today. It converts the original audio signal from time-domain to frequency-domain like
MP3, but in a more direct method. It offers a modular approach to encoding including the so-called “AAC
+” or “aacPlus” variations, properly referred to as HE-AAC (high-efficiency AAC).
There are different modes available within AAC+ itself. Omnia.9/XE provides AAC+ from within its AAC
encoders whenever its SBR (Spectral Band Replication) control is set to “On” or “Oversampled”. When
this control is set to “Off”, encoding is plain AAC.
While these modes and AAC+ are technically still part of the AAC encoding process, they merit their own
sections and will be covered in detail separately.
Advantages
AAC is the most efficient encoder currently available. It provides better quality audio at a given bit rate
when compared to MP3. It has gained acceptance and popularity in recent years and can be decoded by
most players.
Disadvantages
Decoding for AAC is not quite as universal as MP3, but it is nearly so due mainly to its use by Apple in its
iTunes player and iPhone/iPad/iPod portable devices.
Recommended Settings
“Broadcast quality” audio can be achieved at a bit rate of 96 kbps stereo at a 44.1kHz sample rate,
though 128 kbps stereo is recommended for the best quality and fewest audible encoding artifacts. 160
and 192 kbps stereo sound better still, but 192 kbps stereo marks the point of diminishing return where
significantly more bandwidth will yield comparatively small improvements to audio quality.
At 128 kbps stereo, no adjustment to the Final Output Level is necessary. It can be left at 0.0dBFS.
At 96 kbps stereo, we recommend a sample rate of 32kHz and setting the Final Output Level to -1.0.
If you find the need to use a bit rate below 96 kbps stereo, we recommend one of the SBR modes
described in detail below.
Choosing an Encoding Format and Recommended Settings
105