Determine actual latency.

1. [Reaper] Preferences > Audio > Recording > User audio driver reported latency, uncheck.
2. [Reaper] Add track, record something.
3. [Interface] Connect headphones (?) into input.
4. [Reaper] Add track.
   1. Turn off monitor.
   2. Arm for recording.
   3. Set input.
5. [Reaper] Play and set levels so track 1 & 2 roughly match.
6. [Reaper] Record.
7. [Reaper] Track 1: Put a marker (M) at a distinctive point.
8. [Reaper] Track 2: Put a marker (M) at the same point.
9. [Reaper] Double click in the ruler (top) in the space between the two markers (creates a time selection).
10. [Reaper] Right click in the ruler (top) in the space between the two markers > Samples.
11. [Reaper] Bottom, Selection: [from] [to] [number of samples].

Determine reported latency error.

1. [Reaper] Delete second marker.
2. [Reaper] Track 2: Delete item.
3. [Reaper] Preferences > Audio > Recording > User audio driver reported latency, check.
4. [Reaper] Record.
5. [Reaper] Track 2: Put a marker (M) at the same point.
6. [Reaper] Double click in the ruler (top) in the space between the two markers (creates a time selection).
7. [Reaper] Right click in the ruler (top) in the space between the two markers > Samples.
8. [Reaper] Bottom, Selection: [from] [to] [error number of samples].

Set correct latency.

1. [Reaper] Delete second marker.
2. [Reaper] Track 2: Delete item.
3. [Reaper] Preferences > Audio > Recording > User audio driver reported latency, check.
4. [Reaper] Preferences > Audio > Recording > Input manual offset, set samples to [error number of samples]

Check it.

1. [Reaper] Record.
2. [Reaper] Waveforms should match.

• Monitor Input: Next to record icon on track, options are On, Off, Tape Auto Style (off during playback, on during recording - useful if punching in and out).