When we're young, our piano teachers exhort us to "practice each hand separately." They tell us that if we do so, we'll learn our music better.
Yes, this can work for us, but there's another, even better reason for practicing one hand at a time: it helps us experience the music differently.
This is big.
When you're walking a bass line with your left hand and playing chords with your right, for instance, you want to really sound like a duet. Your left hand should sound like a real bass player and your right should be playing chords with rhythmic precision and good voiceleading, just like you would if that's all you were doing.
But all too often I hear pianists doing this and it sounds kind of mushy. The bass line doesn't really groove and the chordal rhythms are stiff and predicable.
The remedy? Practice the hands separately and try to experience the integrity of the part all by itself. For its own sake. Then later, when you put the hands together again, the resulting sound will be much better.
Here's a video of me demonstrating this, on walking bass lines.
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