A fast run is learned slowly: loop just the bars that trip you up, play them at a speed where every note is clean, then raise the tempo a little at a time. Orfeo slows the music without changing its pitch, so it still sounds like the song.
Step by step
Open the song and find the run. Scrub to it with the mouse wheel on the piano roll.
Hold Alt and drag across the run on the piano roll to select a loop. Include a beat or two before it, so you have a run-up.
Click the blinking loop button in the top bar to start looping.
Hold the BPM ▼ arrow until the % readout shows about 60%. See Change the tempo.
Press Space and play along until the run is clean several times in a row.
Click ▲ a few times to go up by a few beats per minute, and play it clean again. Repeat until you reach 100%.
Once it holds at full speed, widen the loop by a bar on each side, so you learn to enter and leave the run smoothly.
