Specifications

Pro Tools|HD Getting Started Guide90
TDM II
With TDM II, there is a separate TDM I/O bus be-
tween 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 7 on page 90.
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
Pro Tools|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.
Another example of how TDM II is more effi-
cient than TDM I is to imagine a single HD Core
card with one Engine chip and two Mixer chips.
The DSPs with plug-in instances associated with
the first Mixer do not need to communicate
with the second Mixer, therefore the time slot
numbers used can be re-used by the second
Mixer to communicate with other DSPs loaded
with other plug-ins.
Time slot usage on Pro Tools|HD 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
Figure 7. TDM bus on Pro Tools|HD hardware
to previous
HD card
to next
HD card
DSP
1
DSP
1
TDM II bus allows individual connections between DSPs
bi-directionally with 512 time slots each at 44.1 and 48 kHz
HD-series card
512
DSP
2
512
DSP
3
512
DSP
4
512
DSP
5
512
DSP
6
512
DSP
7
512
DSP
8
512
DSP
9
TDM bus