Specifications

Chapter 5: DigiRack Real-Time TDM and RTAS Plug-Ins 59
would insert the Dither plug-in on a Master
Fader to reduce session bit-depth from 24-bits to
16-bits. The inserts on a Master Fader track are
always post-fader.
The Dither plug-in has user-selectable bit resolu-
tion and a noise shaping on/off option.
Noise Shaping
The Dither plug-in features a technique known
as noise shaping to further improve audio per-
formance and reduce perceived noise in low-
level signals. Noise shaping utilizes filtering to
reduce noise that falls in the middle of the audio
spectrum (specifically, around 4 kHz). This is the
range where human hearing is most sensitive.
In reality, since the noise plays an important
role in reducing quantization artifacts, the noise
is not reduced, rather it is shifted into a fre-
quency range where it is harder to hear. Essen-
tially, noise shaping lessens our perception of
the noise inherent in dithering schemes by
shifting audible noise components into a less
audible range.
Dither and Output Bit Resolution
Dither has two user-selectable settings for opti-
mizing its operation:
Bit Resolution
Use this pop-up menu to choose one of three
possible resolutions for the Dither processing.
As a general rule, set this control to the maxi-
mum bit resolution of your destination.
16-bit Recommended for output to digital de-
vices such as DAT recorders and CD recorders,
since they have a maximum resolution of 16-
bits.
18-bit Recommended for output to analog de-
vices if you are using an 18-bit audio interface,
such as the 888 I/O or 882 I/O audio interface;
this is the maximum resolution available from
the 18-bit digital-to-analog convertors of these
devices.
20-bit Recommended for output to digital de-
vices that support a full 20-bit recording data
path, such the Sony PCM-9000 optical master-
ing recorder, or the Alesis ADAT XT 20. Use this
setting for output to analog devices if you are us-
ing a 20-bit audio interface, such as the
882|20 I/O audio interface. The 20-bit setting
can also be used for output to digital effects de-
vices that support 20-bit input and output, since
it provides for a lower noise floor and greater dy-
namic range when mixing 20-bit signals directly
into the TDM environment.
Insert the Dither plug-in (or any dithering
plug-in, such as Dither, POW-r Dither, or
Maxim) on a Master Fader track when us-
ing Bounce to Disk to create a 16-bit file (or
any bit depth lower than 24-bit) from a 24-
bit session; otherwise the resulting 16-bit
file will be truncated at the destination bit
depth. For more information on Bounce to
Disk, refer to the Pro Tools Reference Guide.
If outputting 24-bit audio to an analog des-
tination with a 96 I/O, or 192 I/O, you do
not need to use Dither. This allows maxi-
mum output fidelity from the high-perfor-
mance 24-bit digital-to-analog convertors
of the interfaces.