Stem01
Measure the gap at both ends
Put the original recording on an audio track and the converted MIDI on an instrument track. Pick a clear attack near the start and another near the end. If the MIDI leads or lags by about the same amount at both points, move the entire MIDI clip by that amount. If the gap grows, check tempo and clip stretching before editing notes.
02
Check the tempo used for the import
StemMIDI exports a single MIDI track at 120 BPM so the file can encode the recording’s estimated note times. Try the import in a separate 120 BPM project with the source audio playing at its original speed. At 120 BPM, an attack four seconds into the take lands eight quarter-note beats from the start. If the project plays those same eight beats at 100 BPM, the attack lands at 4.8 seconds. That difference points to tempo rather than a misplaced note.
03
Fix the notes that still disagree
Once the start and end of the clip agree with the audio, zoom in on the remaining mistakes. Move a note’s start if the attack is late or early, and adjust its end separately if the sustain is wrong. For piano, check bass notes and rolled chords against the recording. Use quantization only where you want the performance to follow the grid.