Managing Latency

The following article was published in the April 2005 issue of EQ Magazine, and appears courtesy of EQ and Music Player Network.

http://www.eqmag.com/story.asp?sectioncode=44&storycode=7685

Want great results with your DAW? Then you’re going to need to get latency, or timing delays, under control. For our part, we’re going to be looking at some specific examples of how to manage and reduce latency using software settings.

Even with software, though, hardware buffer size has the most direct effect on latency, so this should/must be the first thing you check.

PRO TOOLS

Using Pro Tools LE 6 (6.7) as an example, we can see that the Playback Engine window (found in the Setups menu) contains the “H/W Buffer Size” setting.

Lowering the H/W Buffer Size will reduce the delay experienced when monitoring audio when recording tracks, and with auxiliary and instrument tracks. Users generally find that with the H/W Buffer Size at 128 samples they don’t perceive noticeable delay (at 44.1kHz, that’s approximately 3 milliseconds). Remember that a smaller H/W Buffer Size will increase strain on your host CPU. So watch the CPU meters, and don’t reduce the buffer size so much that you run out of computer power.

Note that Pro Tools’ Playback Engine window contains some additional parameters, including the “DAE Playback Buffer.” Be careful not to confuse this with the Hardware Buffer above. Adjusting the DAE Playback Buffer will not reduce latency, and can in fact hinder performance when improperly adjusted.

DIGITAL PERFORMER

With Digital Performer 4.5, we’ll see a similar parameter in the “Configure Hardware Driver Window” (Setup menu > Configure Audio System).

The “Buffer Size” parameter can be raised or lowered to reduce latency. (Note the “Host Buffer Multiplier” setting below Buffer Size. This setting won’t directly affect latency, and should be kept at level 1 unless you’re using multiple CoreAudio devices at the same time.)

SPECIAL FEATURES

Several applications, including Digital Performer and Pro Tools, have added software features to manage latency so that you don’t have to struggle with hardware buffers. When using Pro Tools with the Digi002 (or Digi002R), “Low Latency Monitoring” can be employed while recording audio.

When enabled, the audio being recorded “takes a shortcut” and uses the internal hardware mixing features in the Digi002 to send input directly to output (as well as the computer), resulting in zero latency. One catch is that any plug-ins inserted on the record tracks will be bypassed while recording. And this feature won’t reduce latency on instrument/aux tracks.

Taking a different approach, Digital Performer 4.5 adds a new feature called “Automatic Plug-in Latency Compensation (found in Setups > Configure Audio System > Configure Studio Settings).

This option is designed to deal with the latency resulting from instrument tracks, powered plug-ins (such as the TC Electronic PowerCore or Universal Audio UAD1), and certain native plug-ins. By “looking ahead,” Digital Performer can anticipate plug-in delays and adjust the entire song to compensate.

(While we’re looking at this “Configure Studio Settings” window, it’s important to note that adjusting the “Buffer size per voice” won’t affect latency.)

Most audio recording apps have some kind of buffer size setting you can adjust to reduce latency. Some also have “low latency” or “latency compensation” features, as in the examples above. Be sure to check documentation for your software to make sure you’re making the proper adjustments.

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