Sonnox Fraunhofer Pro-Codec User Manual
Page 32
5.9 HD-AAC
5 THE PRO-CODEC PLUG-IN
button enabled, the audition point is
after the HD-AAC encoder-decoder.
You will notice that the
DIFF signal in the FFT display will drop below -144 dB. (HD-AAC is
lossless to 24 bits, so the
DIFF signal has an amplitude smaller than 24 bits down. If the
input signal to the codec is quantised to 24 bits, either by dither and truncation, or
because it is unprocessed data from a 24 bit input file, the
DIFF signal will drop below
-180 dB).
While encoding/auditioning an HD-AAC signal, attention should be paid to the lossy core.
We recommend selecting the appropriate core codec in an adjacent codec row, which will
allow correct auditioning of the lossy codec in the HD-AAC channel, and will also allow
correct overload monitoring and mitigation.
The HD-AAC lossy core takes the parameters:
Bit rate
Selectable from 96kbps to 192kbps
Mode
CBR
Quality
Medium
However, remember that if the Bitstream Level
TRIM function is used to mitigate the core
codec overload, and if that same trim value is applied to the HD-AAC encoder input, then
both the lossless and the lossy data streams will be trimmed.
Also note that, under normal circumstances, if the lossless codec’s Bitstream Level
Trim
is non-zero to avoid clipping in the lossy chain for an offline encode that uses the online
trim values, then the resulting decoded output file will not be lossless because the level
has changed.