Any DAW application will add some latency to playback when using a VST plug-in like the ARIA Player. This can often be addressed by changing buffer size settings in the DAW application. Reaper's default settings for buffer size add an estimated 185ms between when a note is triggered and when you actually hear it - this is enough to be very noticeable. You can circumvent this problem by changing Reaper's buffer settings:
- Open Reaper.
- Go to Options > Preferences.
- Choose the Audio > Device category on the left.
- The default setting is 8 x 1024 samples. Decrease these values to decrease latency.
NOTE: The exact values will depend on the capabilities of your computer's audio and processing hardware.
Please note that as you decrease the buffer size settings, you may encounter poor audio quality, possibly to the point of no playback. This indicates that your computer's hardware cannot handle such low settings, and you will need to increase the buffer size.