System Configuration : System Setup : Configuring Pro Tools System Settings : Delay Compensation Engine

Delay Compensation Engine
Depending on your Pro Tools system, the Delay Compensation Engine setting in the Playback Engine determines how much DSP or host-based processing resources are dedicated to Pro Tools Delay Compensation, which manages DSP and host-based delays in the Pro Tools mixer.
Within a session, you can enable or disable Delay Compensation (Options > Delay Compensation). When Delay Compensation is disabled, it uses no DSP or host-processing resources.
To configure the Delay Compensation Engine:
1 Choose Setup > Playback Engine.
2 From the Delay Compensation Engine pop-up menu, select None, Short, Long, or Maximum.
3 Click OK.
Delay Compensation Settings
Depending on your Pro Tools system, there are up to four settings available in the Playback Engine to dedicate processing resources for Delay Compensation:
None
Allocates no resources for Delay Compensation.
Short
Provides 1,023 samples at 44.1/48 kHz, 2,047 samples at 88.2/96 kHz, or 4,094 samples at 176.4/192 kHz of Delay Compensation for each channel. This is the most efficient setting. For sessions with only a few plug-ins that do not induce too much DSP and host–based delay, this setting should be sufficient.
Long
Allocates 4,095 samples at 44.1/48 kHz, 8,191 samples at 88.2/96 kHz, or 16,382 samples at 176.4/192 kHz of Delay Compensation for each mixer channel. For sessions with a lot of plug-ins resulting in a large amount of DSP and host–based delay, select this setting.
Maximum
Allocates 16,383 samples at 44.1/48 kHz, 32,767 samples at 88.2/96 kHz, or 65,534 samples at 176.4/192 kHz of Delay Compensation for each mixer channel. For sessions with plug-ins on mixer channels that result in more the 4,000 samples of delay at 48 kHz, select this setting.
*
Pro Tools HD with Avid HDX hardware acceleration always uses the full DSP resources of the Maximum setting when Delay Compensation is enabled. The None, Short, and Long settings are included only for compatibility with legacy sessions.