Tuneful, musical, melodious, harmonious, sweet-sounding. archaic. spec. Of a peal of bells: in first 2 quots., well-tuned, in tune.

Of an instrument, the voice, etc.: finely or properly tuned; having a good tone; (of music or sound) tuneful, melodious. Also of a group of…

Brought into harmony, or to right musical pitch, harmonious, accordant.

That has been modulated (in various senses).

Of a musical instrument: tuned very precisely, so as to play at exactly the correct pitch. Often (and now usually) in figurative contexts.

Suitably modified, harmonized, attuned.