Specifications

Pro Tools Reference Guide38
Hardware Buffer Size
The Hardware Buffer Size (H/W Buffer Size) con-
trols the size of the hardware cache used to han-
dle host-based tasks such as Real-Time Audio-
Suite (RTAS) plug-in processing.
◆ Lower Hardware Buffer Size settings reduce
monitoring latency, and are useful when you are
recording live input.
◆ Higher Hardware Buffer Size settings allow for
more audio processing and effects, and are use-
ful when you are mixing and using more RTAS
plug-ins.
To change the Hardware Buffer Size:
1 Choose Setups > Playback Engine.
2 From the H/W Buffer Size pop-up menu, select
the audio buffer size, in samples.
3 Click OK.
CPU Usage Limit
The CPU Usage Limit controls the percentage of
CPU resources allocated to Pro Tools host pro-
cessing tasks.
◆ Lower CPU Usage Limit settings limit the ef-
fect of Pro Tools processing on other CPU-inten-
sive tasks, such as screen redraws, and are useful
when you are experiencing slow system re-
sponse, or when running other applications at
the same time as Pro Tools.
◆ Higher CPU Usage Limit settings allocate
more processing power to Pro Tools, and are
useful for playing back large sessions or using
more real-time plug-ins.
With Pro Tools 6.x, the maximum CPU Usage
Limit is 85 percent for single-processor comput-
ers (except for Digi 002, which has a limit of 99
percent), and 99 percent for multi-processor
computers. (The 99 percent setting dedicates
one entire processor to Pro Tools.)
To change the CPU Usage Limit:
1 Choose Setups > Playback Engine.
2 From the CPU Usage Limit pop-up menu, se-
lect the percentage of CPU processing you want
to allocate to Pro Tools.
3 Click OK.
Number of Voices
(TDM Systems Only)
On TDM systems, the Number of Voices setting
lets you control the number of available voices
and how those voices are allocated to DSPs in
your system. For example, the default number
of voices on a Pro Tools|HD 1 system is 48
voices, using one DSP (at sample rates of
44.1 kHz or 48 kHz).
Depending on the current sample rate and the
number of TDM cards in your system, you will
have different choices for voice count. For voice
limits on different Pro Tools|HD systems, see
“TDM System Playback, Recording and Voice
Limits” on page 7.
In addition to causing slower screen re-
sponse and monitoring latency, higher
Hardware Buffer Size settings can affect the
accuracy of plug-in automation, mute data,
and timing for MIDI tracks.
Increasing the CPU Usage Limit may slow
down screen responses on slower computers.
Changing the number of voices affects
DSP usage, the total number of voiceable
tracks, and overall system performance.