“His voice was low, charged with unspeakable adjectives.”
-Frank Herbert
Booming: loud, deep, and attention-grabbing
Dead: if a person's voice is dead, they sound emotionless and probably monotoned
Flat/monotoned: dull, lacking variation in tone, bored
Grating: irritating, unpleasant, raspy, annoying, etc.
High-pitched: shrill
Plummy: describes the way English people of the upper class talk and the word is typically used with derogatory connotations
Soft-spoken: speaking with a gentle or soft voice
Strident: loud and harsh; very similar to 'grating'
Thick: if your voice is 'thick with emotion', it is generally deeper and unclearer than normal
Tremulous: unsteady or shaky because of emotions
Quavering: if a person's voice is quavering, their voice is trembling (usually due to nervousness)