Although most actors can speak Mandarin now, there are still some actors who can't. Or you don't speak Mandarin very well.
If the original sound is used instead of the second dubbing, it will be unacceptable to the audience. In addition, some actors from other regions, such as Guangdong, Hongkong or Taiwan Province Province, may have some Cantonese accents.
But they can't speak Mandarin. At this time, they need a second dubbing to cover up this deficiency! The second reason is to eliminate noise!
We can't hear any noise when we watch a movie. What I hear is the comfortable actor's voice and background music.
But in fact, when shooting, a lot of noise will be recorded. The easiest way to eliminate noise is to eliminate the original sound and dub it directly twice.
In this way, the original sound of the actors and the voices of some extras will disappear. You need to dub them again!
So this is the second reason, in order to eliminate noise! The last reason is that it is more rigorous!
The use of secondary dubbing is actually to be more rigorous! Because the second dubbing, the dubbing actors used are all professional dubbing actors! They are all dubbed after dubbing training.
If you don't dub it twice, some lines or places will be imprecise! Or it sounds strange.
But after the second dubbing, these problems will not appear. So, this is the last reason, in order to be more rigorous!