In the film Rogue One: A Star Wars Story, there is a scene at Darth Vader's castle on Mustafar where we can see Vader fully submerged in bacta fluid inside his rejuve tank. Then, after the announcing, from his attendant Vaneé, of Director Krennik's arrival, the tank began to empty and we can see part of Varder's head which does not appear to wear any hearing aid. I ask, is there a canon or legend explanation about how is possible that Vader can hear his attendant’s voice?