The audio buffer size is set to a high value
The audio data produced by a software instrument is temporarily stored in a buffer. This audio buffer must be completely filled before it is transferred the sound card and your speakers. The larger the buffer, the longer it takes until you actually hear a sound after pressing a key on your MIDI keyboard.
At a sample rate of 44.1 KHz and an audio buffer of 512 samples, it takes approximately 11ms to fill the buffer, whereas with a buffer size of 256 samples this takes approximately 6ms. These are the theoretically minimal latencies with these buffer settings. The sound card driver, digital/analog conversion etc. may add their bit to this value.
In 6ms sound travels approximately 2 meters. This is a very common distance between live players and monitor speakers. So 6ms seems to be an acceptable and unnoticeable latency.
Latencies below 6ms are barely noticeable when playing an instrument. Thus it's recommended you set the audio buffer size to 256 samples or lower for live playing of software instruments. A larger audio buffer unburdens the CPU and leads to a better performance, but at the cost of a higher latency. Try different buffer settings to find the best value for your personal setup and taste.
The audio buffer size is set in Preferences > Audio... > Drivers > I/O Buffer Size.
The software instrument is processed on a Node
When a software instrument is processed on a Node computer, the audio data has to be transferred to the Node computer and back to the Logic host. This introduces additional latency which is automatically compensated for during playback. When playing live, this latency cannot be compensated for. Switch off the Node buttons of the Audio Instrument tracks you want to play live.
A mastering plug-in can introduce latency
A mastering plug-in, such as the Adaptive Limiter, which works with a large look-ahead, has been inserted in the master output or into the Audio Instrument track. These plug-ins also introduce latency which cannot be compensated when playing live. Disable mastering plug-ins for live playing Audio Instruments.
This document will be updated as more information becomes available.