Atmosphere on set
Usually an actor’s voice is recorded directly on set, and it’s a big difference whether someone says something in a factory hall (e.g. in the final scene of The Departed) or on a beach or in a forest. A resonating echo, the sound of breaking waves or the creaking of the undergrowth are an inherent part of an actor’s performance and of the atmosphere which makes many movies what they are.
In a dubbed movie, on the other hand, you can easily hear that the voice actors are sitting in a studio. The result is an audio track that’s completely flat, lacking any kind of atmosphere. Sometimes it’s even just words that create an atmosphere, for example the conversation between Death and Max von Sydow in Ingmar Bergman’s The Seventh Seal: ‘Vem är du?’ – ‘Jag är döden.’ – ‘Kommer du för att hämta mig?’ (‘Who are you?’ – ‘I am Death.’ – ‘Are you coming to get me?’)
The Seventh Seal
Every language sounds differently – and the sound of a language is a major part of the art form film. Especially languages which differ greatly from Indo-Germanic and Romance languages are very difficult to dub, because a Korean speaking Korean in Korea, sounds very strange if he’s suddenly a Korean speaking French in Korea. Especially those kinds of languages have very unique phonetics, which often have a lot to do with mimics and gestures. That interaction is often lost when a movie is dubbed. Not to mention the often very confusing, non-existent lip sync.