Specifications

Expanded Systems Guide16
RTAS Monitoring Latency with
Expansion|HD
Systems using the Digidesign Expansion|HD
chassis will incur increased latency when moni-
toring the output of RTAS plug-ins, compared
with systems where the Pro Tools|HD cards are
installed in the host computer. This increase in
RTAS monitoring latency is due to the hardware
buffering needed for the Expansion|HD chassis.
A Pro Tools Hardware Buffer setting of 256 sam-
ples on a Digidesign Expansion|HD system in-
curs the same RTAS monitoring latency as a
hardware buffer setting of 512 samples on a sys-
tem with the HD cards installed in the host
computer. This increase in monitoring latency
may be noticeable when playing RTAS virtual
instrument plug-ins in real time.
RTAS monitoring latency can be reduced by de-
creasing the Hardware Buffer setting in
Pro Tools. However, decreasing this setting may
affect other areas of system performance.
To minimize RTAS real time monitoring latency
when using the Digidesign Expansion|HD:
1 Launch Pro Tools.
2 Choose Setup > Playback Engine.
3 Set the HW Buffer to half of its previous set-
ting (before you installed the Expansion|HD
unit). For example, if the HW Buffer setting is
256 samples, set it to 128 samples.
Specifications
This section provides slot layout and technical
specifications for the Digidesign Expansion|HD.
Slot Layout
The Digidesign Expansion|HD Chassis has slots
that are numbered sequentially, right-to-left
when viewed from the front (1–6).
When Delay Compensation is active in
Pro Tools, any delays incurred due to RTAS
monitoring latency are correctly compensated
during playback.
The Digidesign Expansion|HD is for
Pro Tools|HD (for PCI) cards only. It does
not support Pro Tools|HD (for PCIe) cards,
SCSI HBA cards, video cards, FireWire
cards, or other special-purpose cards.
Slot numbering for Digidesign Expansion|HD
654321