Day-Lewis, who plays the 16th president in Steven Spielberg's epic film biography "Lincoln," which goes into wide release this weekend, settled on a higher, softer voice, saying it's more true to descriptions of how the man actually spoke.
"There are numerous accounts, contemporary accounts, of his speaking voice. They tend to imply that it was fairly high, in a high register, which I believe allowed him to reach greater numbers of people when he was speaking publicly," Day-Lewis said in an interview. "Because the higher registers tend to reach farther than the lower tones, so that would have been useful to him."
"Lincoln" is just the fifth film in the last 15 years for Day-Lewis, a two-time Academy Award winner for best actor ("My Left Foot" and "There Will Be Blood"). Much of his pickiness stems from a need to understand characters intimately enough to feel that he's actually living out their experiences.
The soft, reedy voice of his Lincoln grew out of that preparation.
"I don't separate vocal work, and I don't dismember a character into its component parts and then kind of bolt it all together, and off you go," Day-Lewis said. "I tend to try and allow things to happen slowly, over a long period of time. As I feel I'm growing into a sense of that life, if I'm lucky, I begin to hear a voice.
"And I don't mean in a supernatural sense. I begin to hear the sound of a voice, and if I like the sound of that, I live with that for a while in my mind's ear, whatever one might call it, my inner ear, and then I set about trying to reproduce that."
Lincoln himself likely learned to use his voice to his advantage depending on the situation, Day-Lewis said.
"He was a supreme politician. I've no doubt in my mind that when you think of all the influences in his life, from his childhood in Kentucky and Indiana and a good part of his younger life in southern Illinois, that the sounds of all those regions would have come together in him somehow.
"And I feel that he probably learned how to play with his voice in public and use it in certain ways in certain places and in certain other ways in other places. Especially in the manner in which he expressed himself. I think, I've no doubt that he was conscious enough of his image."