Everyone who teaches guitar says that you should practice slowly because that is the best way. One example is here, but there are billions of others who say it too.
I try to take their advice to heart, but it frustrates me because "slow" is relative so what is it? I'm a numbers person so I want exact definitions, not "slow enough."
For example, I'm practicing a piece by Carulli called Andante Grazioso arranged by Eythor Thorlaksson and I'm playing it at a slow tempo of 40 bpm(*). The piece is 64 bars long (including repeats) and 3 beats/bar meaning one play through takes about (64 * 3 * 1.5 = 288 seconds) five minutes.
How do I know if that is slow practice or fast practice? The only definition I've heard is that you shouldn't play a piece faster than you can play it perfectly. What is perfect? Obviously unattainable for a human, what you want is "good enough." So what is good enough? Much harder to attain for a self-critical person who is good at spotting errors.
I can play the piece "really good" (to my untrained ears, that is!) at that slow tempo. If I increase the tempo to 60 bpm, with minor faults, to 80 bpm with major faults and to 100 bpm with glaring errors.
And almost as obviously, I can play it even better at 30 bpm or 20 bpm! But why stop there? 10 bpm or one note every six second because if slow is good, then slooooooooooooow is better. :)
Essentially, I'm looking for a number between 0-120 which is the bpm value I should set my metronome to when practicing this piece to receive the most guitar skill/time unit invested. I also want to know what logic I should use to figure out what this bpm value is when practicing other pieces.
- I know classical music isn't supposed to be played at a fixed tempo, but more fluidly. But I'm not good enough for playing like that yet.