Specifications

Appendix B: TDM Mixing and DSP Usage 595
Appendix B: TDM Mixing and
DSP Usage
Benefits of TDM II
Digidesign’s TDM (or time division multiplexing)
technology is based on the concept of a single,
high-speed data highway, or bus that transmits
data between your Pro Tools CPU, Pro Tools
cards, and the DSP chips on the cards.
Pro Tools|24, and Pro Tools|24 MIX-series cards
feature Digidesign’s original TDM bus design.
Pro Tools HD-series cards feature Digidesign’s
new and enhanced TDM II architecture. The
TDM II architecture provides many advantages
over the original TDM architecture in terms of
its mixing capacity and flexibility.
With both systems, individual channels from
sources such as audio tracks, sends, or busses are
sent out from Pro Tools audio cards, and com-
bined together or multiplexed onto the TDM bus
so that all signals can travel simultaneously and
can be accessed within a single sample period.
At the receiving end, the audio cards can listen
to any connection on the bus, and take what-
ever data they need.
The TDM bus runs fast enough to accommodate
many audio signals at the same time. Each sep-
arate audio signal or stream, takes up a single
time slot on this multiplexed bus.
One of most powerful features of the TDM ar-
chitecture is that a single time slot can be used
to “broadcast” data to many destinations simul-
taneously. With TDM II, not only can it send
data to many destinations simultaneously, but
it can also send signals both bi-directionally and
“privately” between DSP chips, which effec-
tively provides a much greater number of avail-
able time slots. This provides a greater potential
number of connections for routing, processing
and mixing audio signals within Pro Tools.
The examples that follow illustrate how the
original TDM I bus and TDM II differ in their
handling of data.