这是一个著名的录音师说的关于Adr的问题，注意其中一句，演员在录音棚里面一般是没有台词或剧本的。
Randy Thom:
The way ADR is treated and approached is symptomatic of how little respect sound gets in the movies. You march the actor into a cold sterile room and usually give them no time to get into the character or rehearse. They are expected to just start performing a few minutes after they walk into the room. The emphasis is almost always on getting the dialogue in sync instead of getting the right performance. Of course the majority of the actor's brain is then occupied with whether his lips are flapping at exactly the same rate as they were on the day that the camera was rolling. It is no wonder that most ADR is not very good. In the final mix, directors almost always prefer the production sound, even if it is noisy and distorted.
One of the things you do with ADR to make it sound more like production sound is to pitch it up. ADR is almost always delivered at a lower pitch because the actor doesn't have the energy he/she had on the set. In the excitement of the shooting set the actor tends to talk louder and higher. In an ADR session, the director typically has to push the actor to get them anywhere near the level of vocal performance that came from the set.
If the recording of ADR were treated more like shooting the movie it would almost certainly be better. Recording it in more authentic environments (instead of studios) tends to help the actors' performance enormously. Environmental noise is a problem whenever you record outside of a studio, but well worth the trade-off in my opinion