To Day-Lewis, who claimed the Oscar for best actor as a ruthless oil baron in "There Will Be Blood", the sound of his Daniel Plainview was critical.
"I must have gone over hours of "Dust Bowl" recordings," he says. "The accents and tone can be one of the hardest things to get right, but if you don't, you'll lose your audience."
Bob Corff, author of "Achieving the Standard American Accent" and voice coach to actors including Bardem, Faye Dunaway and Forest Whitaker, says the key to a menacing tone can be just … slowing … down.
"Whether you're looking for a drunk or villain accent, it's very effective to speak your words carefully," Corff says. "In either case, you're trying to hide your true nature. And that's chilling. You don't need to be theatrical if you're saying 'I'm going to cut your head off.' That's scary enough."
The patriarch of modern cinema villainy, James Earl Jones, calls Day-Lewis' threatening monologue in Blood "the scariest thing I've heard in years. The scene where he says, 'One night, I'm going to come to your home and cut your throat.' It was so cold, so disaffected."
Jones says it wasn't until his second film playing Vader that he learned what it takes for a voice to make spines tingle.
"At first, I was trying to put heart in character, and (director George Lucas) said that was the problem," Jones says of Vader in 1977's Star Wars. "He wanted something that could witness and cause all this destruction and not be moved by it."
By 1980 with "The Empire Strikes Back", he understood what Lucas meant. In preparing Jones' lines, Empire director Irvin Kershner read the part into a tape recorder to give Jones a sense of the cadence and rhythm of the voice.
"I thought he did a better Darth Vader voice than I did," Jones says. "It was a little raspy, and completely cold. It seems to be what Heath has done for "Batman"."
Certainly, Ledger's fatal prescription-drug overdose in January also has lent a haunting nuance to a role that has become his swan song. Whether audiences can separate actor from character will decide the destiny of the film — and the lasting memory of the star.
But Nolan says The Joker's on-screen creepiness comes from Ledger's skills, not his fate.
Ledger had one goal in creating the Joker's voice: unpredictability, Nolan says. Ledger moves his voice a full octave up or down in the role — peppering it with a maniacal laugh — a vocal performance that even crewmembers were talking about.
"The crew has some very sharp imitators on it," Nolan says. "They could do a good Batman, but no one could get The Joker. Heath wanted his voice to be as unexpected as his character. You never knew what the character was going to do, and you never knew how he was going to talk."
Voices, particularly in a genre such as comic-book movies, can be freeing for an actor, Bale says. "You can feel pretty silly in a rubber suit," Bale says. "But if you allow yourself to fully get into character, to embody what you're playing, it helps on screen."
And few are questioning that it helped Ledger. A few months ago, director Ang Lee heard Ledger hissing the line "Let's put a smile on that face" as Lee walked through the ShoWest convention of theater owners.
Lee, who directed Ledger in "Brokeback Mountain", initially did not recognize the voice until he looked at the screen.
"I couldn't believe that was Heath," Lee says. "He was such a different person, used such a different voice for "Brokeback Mountain". It's haunting, how much he disappeared into his characters. It wasn't until I heard that, that I realized just how gifted he was with his voice."