(of music or of somebody’s voice) sounding sweet and smooth; very pleasant to listen to (Oxford)
having a pleasant and flowing sound (Cambridge)
She has a softly mellifluous voice. (Cambridge)
We listened to the mellifluous sound of the cello. (Cambridge)
mellifluous voice
mellifluous sound
Harmonic
Pleasing
Harsh
Inharmonious
Mellifluous