Specifications

Pro Tools Reference Guide596
TDM (or TDM I)
The TDM I architecture has a single bus where
every DSP within the entire TDM system shares
a single pool of 256 time slots. See Figure 49. In
practice, this means, for example, that if an au-
dio track has a Reverb One plug-in insert, one of
the 256 time slots is used to connect the Engine
DSP on one chip to the Reverb One plug-in DSP
on another chip. The TDM time slot used comes
from the pool of 256 time slots, and is unavail-
able for use by the rest of the system.
TDM II
With TDM II, there is a separate TDM I/O bus
between each DSP chip on the Pro Tools cards,
each with up to 512 bi-directional time slots at a
session sample rate of 44.1 or 48 kHz (both be-
tween DSPs on each card, and between the DSPs
that communicate between cards). The DSP
chips are arranged serially, with a TDM I/O bus
connecting one chip to the next. This means
that every TDM II connection need only use
time slots between the two DSPs that are being
connected. See Figure 50 on page 597.
So, using the same example as above, if an audio
track has a Reverb One plug-in insert, a time slot
is used between the Engine DSP (sending out the
audio track) and the DSP with the Reverb One
instance. If the Reverb One insert is handled by
a DSP that is physically next to the DSP han-
dling mixing tasks, as shown in the illustration
below, this leaves time slot 2 available for use
between DSP 3 through DSP 9, and subsequent
HD cards.
The maximum consumption of the time slots
for a single connection occurs when the audio
must be sent between the first and last DSP in
the system. In this instance, a time slot between
each DSP is used to reach the last DSP in the
chain.
Figure 49. TDM bus on Pro Tools MIX-series hardware
DSP
1
DSP
2
DSP
3
DSP
4
DSP
5
DSP
6
TDM bus
256 time slots for entire system
Engine Mixer ReverbOne
to previous
MIX card
to next
MIX card
MIX-series card
Time slot usage on Pro Tools MIX-series hardware
1
slot 1 (used)
slot 2 (used)
DSP
1
DSP
2
DSP
3
Engine Mixer ReverbOne
256
Time slot usage on Pro Tools HD-series hardware
slot 1 used slot 1 free slot 1 free
DSP
1
DSP
2
DSP
3
Engine Mixer ReverbOne
slot 2 used slot 2 used slot 2 free