Hell, putting on headphone on a prisoner with extremely irritating sound won't give that prison any permanent damage but may cause them to give you information due to stress. Aren't their drugs out there that will result in false pain? I believe there are, so that's a good option.
By allowing torture you open the floodgates of hell. By definition torture must hurt, meaning it must be a traumatic experience for the victim. There is no humane way of doing it.
Torture is not compatible in any way with the presumption of innocence, and there is no reason why we should abolish this essential pillar of western civilization.