Meaning.
Voicemaster is a term that comes up frequently in LoA's stories. It is a title given to someone who can imitate voices ranging from falsettos to deep basses and animal sounds. Talent for a voicemaster is very rare and supposedly there are only a handful of voicemasters in each generation.
Limitations of a Voicemaster.
A female Voicemaster usually can't imitate a man's voice. Also a man who carries the title and tries to imitate a girl's falsetto will find it difficult.
List of Voicemasters.
Adeline Dragon. Pilot League. Her highest and clearest range is Purpure's falsetto while Crystal Lion's voice is the deepest she can go. Any deeper and she'll get a sore throat. Actually she can talk in a higher falsetto but Purpure's falsetto is much more popular than her little girl slut falsetto.
Wolf Piper. Highest range sounds like a young puppy.