Thanks to cumberbatchinfobank.com for the interview and Y for the translation (paraphrasing) :)
Q: How was the voice of John Harrison created?********Benedict explains he discovered that voice, that way of speech as he was trying to figure out the kind of person he is. Although John Harrison seems at first glance to be a man without any compassion, he is in fact a very passionate man, which actually is the source of his fierce need for revenge. That’s how he wanted to play Harrison, so he used a very controlled voice that was full of fearsome authority but calm and soothing at the same time that would make people fear him but trust him at the same time. Benedict says he tried to create a powerful, stable voice for John Harrison.*******Q: How did you acquire your voice?*******Benedict jokes, he did so by smoking occasionally, drinking whisky…which is a lie, he says. He says his voice is a British thing, part of the British tradition that places value on not just the physicality of the actor or a grand spectacle but places value also on how words sound and the way an actor speaks. His voice is a product of understanding the importance of those things. Their language is the language of Shakespeare, after all, and so that might also be a part of him.*******Q: Does finding the voice play a part in finding the character?*******Benedict says in his case of approaching new roles, he often starts with finding the voice for his character, how the person communicates in various situations. In some cases, the dialect or accent determines how one’s body moves. The voice of a character isn’t separate from everything else, so he tries to use everything (voice, body, etc) in his performance.********Q: Have you ever found it difficult to find the voice for a certain character?********Benedict says when he was a student, he often had to play roles much older than he actually was, so there were times he tried to gain a deeper, more mature voice by smoking Marlboros and drinking whisky, not that he would ever recommend that to young people. As a theatre actor he was blessed with wonderful voice trainers, so he learned a lot from them, not just the quality of the voice but the importance of maintaining your voice.