Specifications

Pro Tools|HD Getting Started Guide94
Mono and Stereo
Each TDM mono or stereo mixer is of the di-
mensions “N x 2,” meaning that it mixes a vari-
able number of inputs to an output pair. For ex-
ample: A session with six tracks routed to
Output 1–2 would require a single 6 x 2 mixer. If
one of the six tracks is assigned to Output 3–4,
however, two mixers are required—one 5x2
mixer routed to Output 1–2, and one 1x2 mixer
routed to Output 3–4.
Multichannel Surround
Each Surround mixer can have a variable num-
ber of outputs as well as a variable number of in-
puts. For example, the 7.1 format requires eight
outputs. A single mono track assigned to a 7.1
Output or Bus path would require a 1x8 mixer,
while one mono and one stereo track assigned
to a 7.1 Output or Bus path would require a 3x8
mixer.
The important concept here is that every output
(whether they are I/O or bus outputs) requires
that a mixer exists for that output. This means
that creating a send to bus 1 requires that a
mixer be created for the bus 1–2 outputs, and
that mixer will have one input.
Mixing with Sends and Busses
Each send will add an input to the destination
output pair. For example, a send to output 1 will
add another input to the output 1–2 mixer. If
the send destination doesn’t already have a
mixer for its output pair, then a new mixer will
be created. A send to bus 3 will make a 1x2 mixer
for bus 3 if no other bus 3 sources have been cre-
ated yet.
In addition, adding a new track and assigning its
input to a bus source will create a mixer for that
bus pair if there is not one already.
For example, creating a new Auxiliary Input
track and setting its input to bus 5 will create a
1x2 mixer for bus 5, even if no sources have
been created yet.
Submixing
When the number of channels that must be
mixed exceeds the capacity of a single DSP, ad-
ditional “main” mixers are created automati-
cally, along with summing submixers (which
sum together the “main” mixers). The use of
submixers allows large mix configurations to be
created.
For example, on a Pro Tools|HD system, when a
Stereo mixer running at 44.1 kHz needs to grow
to more than 68 inputs, a submixer is created
along with another “main mixer” that provides
“n” number of inputs beyond 68. Both the orig-
inal 68x2 mixer and the new “N x 2” mixer
which provides additional inputs are routed to a
submixer, and its outputs are finally sent to the
desired destination (such as Output 1–2 on your
main audio interface).
Note that any small delays (on the order of a few
samples) that are created remain equal between
these main mixers because they are summed to-
gether by means of submixers, and are not cas-
caded.
The total number of voiceable tracks supported
by your particular Pro Tools configuration will
ultimately determine the maximum number of
channels for your TDM mixer.
Mixers and DSP Hardware
Different mixer plug-ins are available, each of
which uses DSP power at slightly different rates
on the different audio cards (and their DSP
chips), as shown in the following tables.
See “Mixer Plug-ins” on page 97.