DigiDesign Digidesign Pro Tools 8.0, Reference Manual

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Pro Tools Reference Guide 366
Pro Tools LE uses the host processor in your
computer for all audio processing, playback, and
recording, so there is always a small amount of
latency in the system. For example, there may
be some audible delay between the incoming
signal and outgoing signal when monitoring re-
cording through Pro Tools.
With Pro Tools, latency occurs as follows:
• All Pro Tools systems can have RTAS MIDI-
to-audio latency (such as when playing an
RTAS virtual instrument live and monitor-
ing the instrument’s output).
• Pro Tools LE systems have input-to-output
monitoring latency on any record-armed
tracks or Auxiliary Inputs with live inputs.
• Pro Tools|HD systems have monitoring la-
tency on tracks that have one or more RTAS
plug-ins.
The latency amount is related to the
H/W Buffer
Size
setting—the larger the buffer size the
greater the latency. You can reduce the amount
of monitoring latency by reducing the
H/W
Buffer Size
setting. However, even at the smallest
buffer size, there is still some latency.
In addition, reducing the buffer size limits the
number of simultaneous audio tracks you can
record without encountering performance er-
rors.
While there may be times when you want a
larger buffer size, such as when you have higher
track counts with more plug-ins, you will gener-
ally want the smallest possible buffer size when
latency is present during recording and moni-
toring.
For more information on
H/W Buffer Size
set-
ting, see “Hardware Buffer Size” on page 42.
If you are monitoring the recording source with
an external mixer before it is routed to
Pro Tools, you will not hear any latency.
To set the Hardware Buffer Size:
1
Choose
Setup > Playback Engine
.
2
Choose the number of samples from the
H/W
Buffer Size pop-up menu.
3
Click
OK
.
Recording with Delay
Compensation
(Pro Tools HD Only)
Generally, you will want to record with Delay
Compensation enabled to maintain phase co-
herent time alignment between tracks with dif-
ferent DSP delays. However, you will generally
want to avoid using inserts on recording tracks
or tracks used for controlling the levels of cue
mixes. For more information about Delay Com-
pensation, see “Delay Compensation” on
page 860.
Zero Latency Monitoring
(Mbox 2, Mbox 2 Mini, and Mbox Only)
Mbox 2, Mbox Mini, and Mbox give you the
ability to monitor your analog input signals
while recording, without hearing any latency.
This zero-latency analog monitoring is con-
trolled by the front panel Mix knob, which you
can use to blend and adjust the mix between the
interface’s analog input and Pro Tools playback.
For more information, refer to your system’s
Setup Guide .
Computers with slower CPUs may not be
able to use a H/W Buffer Size setting lower
than 512 samples buffer size without en-
countering performance errors.