audio reproduction in a nutshell


2010-04-24 1:52 am
Don't get me wrong - I love illusions. Those kind are even more fascinating in the flesh. I just don't think it is relevant to audio reproduction.

I do see a bit of relevance - good audio system will give the aural "illusion" that the singers and instruments are in the room with you.

But clearly, there's a lot of difference between visual and aural illusions, and research in one is inapplicable to the other.
Maybe closer than you think...hearing and sight both use the differential input between a pair of receptors to decode information about the perceptual scene. In the optical illusion the brain decodes the slightly different scenes from two eyes to construct an apparently solid cube floating in air. In audio reproduction the brain decodes the differences in arrival time, loudness and timbre from two ears to construct an apparently structured soundstage of performers arrayed side to side and fore & aft in the listening room. The common element is, of course, the brain...where signals from the receptors get magically transformed into the (not always 100% correct) construct of the perception of reality.:cool:
I know it's an illusion because little presents don't float in mid-air. Once the nature of the illusion is exposed, one has to work at re-adjusting one's perception to see the thing as what it is supposed to represent.

you are arriving to a conclusion based on previous knowledge. there's the famous story of people fleeing the movie theater when they saw a projection of an incoming train. you hear the illusion because you see the speakers.

suppose there was a curtain between you and a pair of speakers that were playing a violin recording. can you tell whether the sound is coming from speakers or if there is actually a violinist behind the curtain?
Illusions are based on experience of recognition. Recognition works applying 3 filters: deletion, distortion, generalization. In recognition of words all kinds of sensory perception work, otherwise you won't understand words like "Bright", "Sharp", "Loud", "Sweet", and so on. In recognition of speech facial muscles and nerves play major role: if somebody can't pronounce some intonations hearing only can't recognize the difference.

I thought this was about a system that fitted in a nutshell, but it turns out it's about a violinist behind a curtain.

You think you're clever but you can't pull the wool over my ears.


i'm sorry for the misleading title.
i'm making the point that the purpose of a loudspeaker system is to create an illusion.