First, let’s get one thing out of the way: just because a teacher told you that your playing sounds mechanical doesn’t mean it does.
(the teacher might not be expressing themselves very well)
While we’re at it, let’s get another thing out of the way: your mechanical-sounding playing is not the fault of the metronome.
Metronomes are convenient scapegoats here, because after all, they are machines. But, yeah. No.
There are two reasons your playing might sound “mechanical”:
- You’re not playing all the features of the music.
- You’re struggling with the mechanics of playing.
These are totally different.
1. You’re not playing all the features of the music.
If you don’t recognize that there’s a phrase of music, you won’t play it as a phrase. If you don’t recognize a cadence, you won’t play it as a cadence.
When you don’t notice the details that are in the music, you won’t play them. You’ll only play what you do recognize.
This doesn’t mean you’re doing anything wrong. It only means you’re not doing enough right things.
2. You’re struggling with the mechanics of playing.
When you’re fighting with your body trying to get it to do what you want it to do, you’re not giving your attention to the music.
This doesn’t mean you aren’t being “musical”. It only means you’re too distracted by other things to allow your musicality to express itself.
It is wrong to think of playing as being on a continuum with “musical” on one end and “mechanical” on the other end.
That continuum might be useful for the music critic, but it’s not useful for the player.