is described as loud
if it is high in volume
(amplitude, or acoustic energy). By extension, a person who emits noise (with the voice
or otherwise) either loudly or a lot of the time can be described as loud. Whether this is an insult or a compliment is a matter of personal preference: some people self-describe as "loud" while many others consider loud people to be intensely irritating.
See also bel, sone.