Specifications

Pro Tools Reference Guide66
On Avid HDX and Pro Tools|HD systems, chang-
ing engines requires that you quit and relaunch
Pro Tools for the new setting to take effect.
Pro Tools Aggregate I/O
(Mac Only)
On Mac systems using Core Audio, you can use
Pro Tools with the built-in audio inputs and out-
puts on your Mac by selecting any of the available
built-in inputs and outputs, or by selecting the
Pro Tools Aggregate I/O option for using a combi-
nation of built-in inputs and outputs simultane-
ously (for recording and monitoring).
You can configure the Input and Output options
for Pro Tools Aggregate I/O in the Mac Audio
Setup, which can be accessed from the Pro Tools
Hardware Setup.
Hardware Buffer Size
The Hardware Buffer Size (H/W Buffer Size) in the
Playback Engine controls the size of the buffer
used to handle host processing tasks such as pro-
cessing with host-based, or “Native” plug-ins
(AAX and RTAS).
• Lower Hardware Buffer Size settings are useful
for improving latency issues in certain recording
situations or for improving certain system per-
formance problems:
• On all Pro Tools systems, lower settings re-
duce MIDI-to-audio latency (such as when
playing a virtual instrument live and monitor-
ing the instrument’s output). Lower settings
can also improve screen response or the accu-
racy of plug-in and mute automation data.
• On host-based Pro Tools systems, lower set-
tings reduce all input-to-output monitoring
latency on any record-armed tracks or Auxil-
iary Input tracks with live inputs.
• On Avid HDX and Pro Tools|HD systems,
lower settings reduce monitoring latency that
occurs on tracks that have one or more Native
plug-ins. Lower settings can also improve the
accuracy of MIDI track timing on systems
without a MIDI interface that supports time
stamping. Lower settings also improve MIDI
track timing on tracks using MIDI virtual in-
struments that do not support time stamping.
• Higher Hardware Buffer Size settings are useful
for sessions that are using more Native plug-ins
for playback. These settings allow for more au-
dio processing. They can also be useful to re-
duce errors on machines that require a higher
buffer size.
When changing engines on any Pro Tools
system, you may need to reset the default
I/O settings to match the selected audio
interface.
Selecting Pro Tools Aggregate I/O in the Playback
Engine (Mac only)
If you need simultaneous input (recording)
and output (playback and monitoring) with
Pro Tools using the built-in audio options on
Mac, use the Pro Tools Aggregate I/O option.
If you only need to play back audio for editing
and mixing, select the appropriate built-in
audio output option.