An Analysis of the Use of Sound in Hitchcock's "The Birds"

Sound is an important part of any movie. Certainly it's possible to watch a movie on mute but ascertain all the essential information through subtitles or visual cues, but this is still a fraction of the true experience. You miss out on things like actor's voices, like a quivering of the voice betraying a hint of fear or a a soft tone from an otherwise gruff and wizened character indicating a tender reprieve from the norm. But you would also miss out on the ambiance.
Now for horror movies, and Hitchcock in particular, ambiance is a vital component to the overall film. It's hard to feel scared if their is no tension or hint of danger which often owes a lot to a background score or plentiful background noise. However with The Birds Hitchcock goes against the norm and goes entirely without background music. The only sounds for the movie are voices, a few ambient effects, and (most prominently) the sound of the birds.
This is because Hitchcock, when doing research for the film, found a new means of altering sound with the use of computers. Though there are certainly instances of natural bird sounds, many scenes were manipulated in a manner that the sound of the birds almost becomes the films missing score. What's more is that the altered the natural sounds to make the birds sound more otherworldly and sinister. The effect is a classic example of the uncanny, we have a common animal given the sound of some horrible alien creature. Personally, at certain parts, I thought the birds sounded like the devil.
But the absence of a formal score also helps to establish a sort of tension or unease. Take a look at this re-edited version of the final attack scene, where a composer added a soundtrack created to match it.

http://www.youtube.com/watch?v=Lw0FP9putKM


No really, watch the whole thing.
Okay, did you notice a distinct lack of stress? Does it not all of the sudden take on the air of a Disney film or cartoon? The score tends to completely overpower the visuals. It takes the smooth, steady speech of the original scene and turns it into a loudmouth hooligan. There's a subtle removal of the sense of the unknown. Melanie isn't a curious women exploring the house on her own anymore, she's a mannequin being followed by a full orchestra. We are so removed from the scene by these instruments that we are no longer able to relate to the character, but instead hinge our attention on the intrusive sounds. The scene isn't quite ruined, but it is beyond salvation.
Having seen that re-authoring of one of the film's pivotal scenes I think we can say with confidence that Hitchcock made the right choice. In eliminating background music and keeping speech to a minimum he's trimmed the excess from his scenes and presented a much more succinct and effective experience.

References:
http://www.youtube.com/watch?v=Ke1b1j777wU
http://www.zx.nu/ss/chapter8.htm