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)