User`s guide

Appendix B: TDM Mixing and DSP Usage 387
MIX card with two I/Os declared:
16-bit Optimized mixer: 43x2 per chip
24-bit Optimized mixer: 43x2 per chip
Submixing
When there is no space remaining on any
DSP for a single mixer to increase the num-
ber of inputs, summing mixers must be cre-
ated. For example, on a Pro Tools 24 sys-
tem, when a 24-bit Optimized mixer needs
to grow to more than 26 inputs, a summing
mixer is created along with another 1 x 2
mixer to handle the 27th input. Both the
original 26 x 2 mixer and the new 1 x 2
mixer are routed to the new summing
mixer, whose outputs go to the desired des-
tination (such as output 1-2).
Keep in mind that any delays inherent in
creating the summing mixer are equal.
Since input signals are delayed equally,
phase coherency is preserved.
The number of virtual tracks supported by
your particular Pro Tools configuration will
ultimately determine the maximum num-
ber of channels for your TDM mixer.
Sends, Busses, and Master Faders
Each send will add an input to the destina-
tion output pair. For example, a send to
output 1 will add another input to the out-
put 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
3–4 if no other bus 3–4 sources have been
created yet.
In addition, adding a new track and assign-
ing its input to a bus source will create a
mixer for that bus pair if there isn’t one al-
ready. For example, creating a new Auxil-
iary Input track and setting its input to bus
5 will create a 1x2 mixer for bus 5–6, even if
no sources have been created yet.
Mixing Guidelines
The following conditions apply to mixing
with Pro Tools 24 MIX/MIXplus,
Pro Tools 24 and Pro Tools III systems.
One DSP chip is automatically dedicated to
mixing in the TDM environment.
◆ As you reach the basic mixer limits for a
single DSP chip, the system will automati-
cally begin allocating DSP resources from
another chip (if available), making it un-
available for Plug-Ins.
◆ Each bus or send connection requires
DSP to mix signals. This means that each
Send or Auxiliary Input that you create will
use available DSP.
◆ On Pro Tools 24 systems, the 16-bit Opti-
mized Mixer can power more channels per
DSP chip than the 24-bit Optimized Mixer
Plug-In. There may be cases where using
the 16-bit Optimized mixer will help con-
serve enough DSP power to allow for addi-
tional Plug-Ins.
On Pro Tools 24 MIX/MIXplus systems,
there is no advantage to using the 16-bit
Optimized mixer, so you should always use
the 24-bit Optimized mixer.