Manual

Table Of Contents
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It is also advisable to save Presets for the plug-in at a variety of session sample rates and
channel configurations. It is advantageous to categorise the Presets by channel configuration
and session sample rate.
5. Lossless Codecs (mp3-HD and HD-AAC)
A lossless codec is intended to produce an output data stream that is an exact duplicate of an
input audio data stream. In the simple case of a 24-bit wav file as input, the output of the HD-
AAC lossless codec will be a wav file with identical audio data. The behaviour of the mp3-
HD lossless codec is the same when presented with a 16-bit wav file as input.
When these lossless codecs are used in a DAW, the situation is slightly more complicated
because usually the input is not a simple 16 or 24-bit input file. Most DAWs use floating
point processing, and so do most plug-ins. A floating point datum will have many more states
than an audio integer as taken from a 24-bit wav file (this is another way of saying that the
floating point format has higher resolution than the fixed-point wav format). Whenever
processing is performed in a DAW or plug-in, the processing is performed at the higher
resolution of the floating point system, and the resulting audio data cannot be represented
perfectly on a 24-bit scale any more. The data stream will contain floating point values
between the quantised values of the 24-bit scale, and these in-between values are called
‘inters’. This interactivity can be readily seen using the DIFF signal, apparent up to -144dB
for HD-AAC and up to -96dB for mp3-HD. (One of the main reasons the DIFF signal is
included is to aid visibility of this situation.)
The lossless codecs will not reproduce these inter values as they only use a 16 or 24-bit scale,
and the correct terminology is ‘lossless to 24 bits’ for HD-AAC, or ‘lossless to 16 bits’ for
the mp3-HD.
Therefore, if the audio channel includes processing, it is important to present correctly
truncated data to the input of the lossless encoder. When an audio data stream is truncated, it
must first be dithered at the correct level. More on this below.
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