Rubato describes ‘pulling’ a performance in and out of time, to provide a more emotional, sympathetic effect. Here's how it works...
Step 1: We’ve recorded three parts in this track. A main piano figure playing running 1/8th notes and an accompanying strings part, split into higher/lower instruments. Here’s the piano performance with strict quantising. Most emotion is lost to metronomic timing.
Step 2: Here’s the piano as it was recorded live. It’s so tempting to quantise a part when you hear it playing like this, as some notes are early and some are so obviously late. However, it’s in that ebb and flow that musicality lies.
Step 3: So let’s look to capitalise on the musicality of the phrase while eradicating the bits of timing which are sufficiently ‘out’ as to prove distracting. We start by selecting a 45% quantise strength for the notes, which pulls them nearly halfway between their played position and ‘perfect’ timing.
Step 4: This sounds better but we’re not yet hearing rubato. At the end of each four-bar section, we want to hear the piano ‘pull back’, arriving a little late on the down-beat of the fifth bar before picking up the pace again.
Step 5: We can accentuate these moments, pushing the notes leading up to the end of each four-bar phrase late, before then judging the rate of ‘recovery’ of the notes afterwards to get our phrase back in time. We adjust each note manually to achieve this result.
Step 6: We add two more touches. The first is to adjust velocities where necessary, to make sure the phrase flows even more musically. And secondly, we build a rallentando at the end, creating a series of tempo steps to slow down the end of the piece.