Specifications

DigiRack Plug-Ins Guide36
Dither
The Dither plug-in is designed for reducing
quantization noise when mixing or fading low-
level audio signals during word size reduction to
16-, 18-, or 20-bits.
Dither is a form of randomized noise used to
minimize quantization artifacts in digital audio
systems. Quantization artifacts are most audible
when the audio signal is near the low end of its
dynamic range, such as during a quiet passage or
fade-out.
The introduction of dithering can reduce these
quantization artifacts with very low-level noise,
minimizing artifacts as audio reaches low level.
With dithering there is a trade-off between sig-
nal-to-noise performance and less-apparent arti-
facts. Proper use of dithering squeezes better
subjective performance out of 16-bits (or what-
ever the destination bit-depth).
The most common application of dithering is to
use it on a master output mix as the last proces-
sor in the signal path when preparing a 24-bit
session for CD mastering. In this case, you
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.
For more advanced dithering, use the Digi-
Rack POW-r Dither plug-in. See “POW-r
Dither” on page 38.
Dither plug-in
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.