In general OS X already has good monitoring latency but in certain cases you may need to reduce it just a little bit more if you're noticing delay. If you're using the internal mic there is a setting called "Ambient noise reduction" that can be disabled to reduce latency even further. Since Soundtrap already does its own noise reduction this shouldn't affect the quality of your recordings (though of course you should always double check that things sound as you expect.)
To disable ambient noise reduction you can:
- Go to System Preferences -> Sound
- Select the appropriate mic (usually Internal Microphone)
- Uncheck the box that says "Use ambient noise reduction"
Most external microphones don't have this setting but you can always check to be sure.