Gruff voice can signify annoyance or lack of patience, be mindful of the emotional context. The manager's gruff response indicated his irritation with the question.
Pro Tip 2/3
Not Always Angry
Someone's gruff voice might be their natural tone, not connected to their mood or manners. Despite his gruff voice, the old man was actually very kind.
Pro Tip 3/3
Indicative of Characters
In stories, a gruff voice often characterizes a person as tough or rugged. The gruff pirate barked orders at his crew.