Specifications

Pro Tools Reference Guide604
Mixer plug-ins provided with Pro Tools HD-se-
ries systems provide 48-bit precision with 48 dB
of headroom. This means that on the “input”
side of the bus (where signals are summed to-
gether), signals can never clip (even if channel
faders are set to a full +6 dB of gain).
However, the “output” side of the summing
mixer (where the signal is sent in the 24-bit
world of a digital output or onto the TDM bus)
can clip. You can use a Master fader (which does
not “cost” any DSP) to scale the output level of
any mix summing point (a bus or physical out-
put). The master fader's meters will tell you if
you are clipping the mix bus, and the fader can
be used to safely scale the level to avoid clip-
ping, with no loss of quality.
Pro Tools MIX-series systems are supplied with
two mixers, a stereo 24-bit Optimized version
and a Surround mixer. These mixers are almost
identical to those supplied with Pro Tools HD-
series systems, but they provide only 30 dB of
headroom (while still maintaining 48 bits of
precision). Since Pro Tools MIX-series systems
cannot mix as many disk or auxiliary tracks as
Pro Tools HD-series systems, less headroom is
needed to avoid clipping, and this is generally
not a cause for concern.
24-Bit Optimized Mixer
(Pro Tools MIX-Series and Pro Tools|24 Only)
With the 24-bit Optimized Mixer, the Master
Fader meters indicate clipping at both the input
summing stage and the output level stage at all
times. With this mixer, you could lower the
Master Fader to reduce your output level, but
the Master Fader meters could still indicate clip-
ping at the input stage.
In the unlikely event that this occurs—this
mixer's 30 dB of headroom will allow many sig-
nals to be mixed without any input clipping—
simply follow the procedure to trim back your
faders, as described in “Trimming Input Sum-
ming Levels” on page 605.
16-bit Optimized Mixer
(Pro Tools MIX-Series and Pro Tools|24 Only)
With the 16-bit Optimized Mixer, the Master
Fader meters indicate clipping only for the out-
put level stage of the mixer. With this mixer,
you could lower the Master Fader to reduce your
output level, but any clipping at the input stage
would not be indicated.
If reducing the output level has no effect on
clipping, it could be occurring in one of the fol-
lowing places:
◆ At the input summing stage. To prevent clip-
ping at the input stage, trim the input summing
levels.
◆ At an insert on the Master Fader. If you are us-
ing a plug-in on the Master Fader, its meters
show the levels on the insert. To prevent clip-
ping at the insert, trim levels on any plug-ins or
Hardware inserts on the Master Fader.
If you are mixing larger numbers of signals
together, always use a master fader so that
you can monitor levels for the bus (using the
master fader meter), and to trim the result
to avoid clipping. Since Master faders cost
no DSP, there is no reason not to use them.