5.1 DigiRack Plug-Ins Guide - Digidesign Support Archives

38
The most common application of dithering is to
use it on a master output mix as the last processor
in the signal path when preparing a 24-bit
session for CD mastering. In this case, you
would place the Dither plug-in on a Master
Fader as a post-fader Insert to reduce session bitdepth
from 24-bits to 16-bits.
The Dither plug-in has user-selectable bit resolution
and a noise shaping on/off option.
If you are outputting audio to an analog
destination with a 24-bit-capable Pro Tools
system and an 888/24 I/O, do not use
dither. This allows maximum output fidelity
from the 888/24 I/O’s high-performance
24-bit digital-to-analog convertors.
Noise Shaping
The Dither plug-in features a technique known
as noise shaping to further improve audio performance
and reduce perceived noise in lowlevel
signals. Noise shaping utilizes digital filtering
to remove 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 errors (and
thereby audio artifacts) the noise is not reduced
in total, but is shifted into a range where it is
harder to hear. Essentially, noise shaping lessens
our perception of the noise inherent in dithering
schemes by shifting audible noise components
into a less audible range.
DigiRack Plug-Ins Guide
Dither and Output Bit Resolution
Dither has two user-selectable parameters that
allow you to optimize its operation:
Bit Resolution
This pop-up menu allows you to choose one of
three possible resolutions for the Dither processing.
As a general rule, you should set this parameter
to the maximum bit resolution of your destination.
16-bit Recommended for output to digital devices
such as DAT recorders and CD recorders,
since they have a maximum resolution of 16bits.
18-bit Recommended for output to analog devices
if you are using an 888 I/O or 882 I/O Audio
Interface since this is the maximum resolution
available from the 18-bit digital-to-analog
convertors of these devices.
20-bit Recommended for output to digital devices
that support a full 20-bit recording data
path, such the Sony PCM-9000 optical mastering
recorder, or the Alesis ADAT XT 20. This setting
is also recommended for output to analog
devices if you are using an 882/20 I/O Audio Interface.
The 20-bit setting can also be used with
digital effects devices that support 20-bit input
and output, since it provides for a lower noise
floor and greater dynamic range when mixing
20-bit signals directly into the TDM environment.
If you want, you can choose not to use the
Dither plug-in and instead utilize the full 24-bit
resolution of Pro Tools’ digital output, depending
on your destination device. As noted previously,
if you have a 24-bit-capable Pro Tools system
with an 888/24 I/O Audio Interface and are
outputting audio to an analog destination, we
recommend that you do not use dither.