Perhaps a cricket pitch the ground in Perth, Australia is called the WACA (and fits in with your earlier hint of one letter of 'ewer' being correct)
Bugger I thought that was it. Pitch as in music pitch. Pitcher as in tuner = tuning fork. (which can also be used as a pitch fork)
On the right lines there Ron. Think what happens at the very beginning of an orchestral concert - before they play the first piece.
This is worse than going to the Dentist! Other than tune-up, render harmonious or mellifluous, none of which are 4 letters, then I am stumped.