CHORD CHANGES - TRANSITION TIME
I don't see a very important issue sufficiently covered in tutorials on chord changes. Sometimes it is never mentioned.
TRANSITION TIME - the length of time it takes to change from one chord to the next. beginning with the fingers lifting from the strings and ending when the fingers are placed back down in their new position for the subsequent chord.
The end of the transition time usually coincides with the first beat of the bar (beats and bars covered in 1,2,3,4) that being the beat you hear the first downstroke on a new chord.
1 2 3 4 1 2 3 4
↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓
|Em |A C |
* * *
In this example the E minor chord is played for a whole bar, 4 beats. A is played for 2 beats, as is C. We see the A is first hears on the 1st beat of the 2nd bar. That is the end of the transition time the length of time it takes to execute a chord change. That length will be determined by the point at which the chord change begins.
If you could, as it were, pin the tail on the donkey and mark exactly where you would begin the change or where you think you begin them. If you can play this passage, the rhythm is 1 downstroke for each beat, check the moment. when do the fingers leave the E minor and head for the A major?
this is my marker. the moment i would begin the change. Probably earlier than you might think or you might leave it yourself.
...3 & 4 & 1 & 2 & 3...
... * |A * C
Beginning your change here, ashade before the upstroke between the 4th and 1st beat gives you more time and that means arriving just in time for the first downstroke on the A without rushing and being more accurate. the strings on the upstroke before a chord change finishes is usually on open strings, string played unfretted as the fingers have already started their journey to the next chord.
This is absolutely fine, most chords contain open strings and often sounds even better than leaving the change til after that upstroke which leave minimal time for the change and will ultimately slow down progress. There is a finite limit to how fast the fingers will move. Leaving earlier than you think is necessary increases the top speed at which this becomes a problem.
Chord changing is usually a problem of the playing hand setting a fast tempo which is the tempo at which it is least possible to finetune the precise moment to change or even pinpoint the moment at which to begin the change. Old habits will always die hard and new skills are difficult to acquire so learning to slow down and walk through this (rehearsal tempo) rather than running (performance tempo) is essential. It does need some crawling first (practice tempo).