Apple Logic Pro 8 - Manual (Page 849)

Chapter 37 Working With Plug-in Latencies 849
Working With Plug-in Delay Compensation
The Compensation menu in the Logic Pro > Preferences > Audio > General tab allows
you to either disable plug-in delay compensation (Off ), or activate it for:
 Audio and software instrument tracks.
 All channels (audio, instrument, aux, output, bus, and ReWire).
About Plug-in Delay Compensation
Logic Pro provides plug-in delay compensation for all channels: If activated, Logic Pro
compensates for latency introduced by plug-ins, ensuring that audio routed through
such plug-ins is synchronized with all other audio.
Logic Pro achieves this by calculating the amount of latency caused by plug-ins, and
then delaying audio streams by an appropriate amount—or shifting instrument and
audio tracks forward in time. The compensation method depends on the type of
channel that the latency-inducing plug-in is inserted into.
 If latency-inducing plug-ins are inserted into aux or output channels (or ReWire
channels, if used), Logic Pro delays all other audio streams by an appropriate amount.
 If latency-inducing plug-ins are inserted into audio or instrument channels, Logic Pro
automatically shifts these tracks forward in time. The advantage of this method is
that other channels (that do not contain latency-inducing plug-ins) do not need to
be delayed.
As an example: Imagine a simple song with a few bass, guitar, vocal, and drum tracks.
The bass track is routed through an audio channel that contains an effect that
introduces a latency of 10 ms. All guitar tracks are routed to an aux channel that
contains several inserted effects. The combined latency introduced by these effects is
30 milliseconds (ms). The vocals are routed through another aux channel that has a set
of effects that introduce 15 ms of latency. The drum tracks are routed straight to the
main outputs, without being routed through any effects. If latencies were not
compensated for, the drum tracks would play 30 ms ahead of the guitar tracks. The
bass track would play 20 ms ahead of the guitar track, but 10 ms behind the drums. The
vocals would play 15 ms before the guitar track, but 15 ms behind the drums and 5 ms
behind the bass. Needless to say, this isn’t ideal.