I'd like to know what are the differences in timbre – or the acoustic properties of a sound – that allow us to differentiate between a sound which is quiet (but close-by) and one which is far away.
For example, you can tell when someone near to you is playing an instrument quietly even without looking to see where they are – they don't sound 'far away'.
Hearing a loud gig or a car stereo playing from the next street doesn't sound like it's quiet – it sounds loud, but far away.
But other times we can't differentiate – I sometimes hear a siren on TV and think it's on the street!
I thought only the amplitude (i.e. volume) of a sound wave diminished with distance – does the shape/frequency alter too?
Is this ability just to do with having two ears to locate the source – surely someone who is deaf in one ear can still tell an orchestra is playing a diminuendo and not gradually getting further away?!
Best Answer
There are different cues to the perception of distance:
These different cues (maybe more, and mainly the two first) are weighted in your brain to give a stable assessment of distance. Research shows that the weighs associated with these cues vary with the type of signal (noise or speech), and angular position of the source [2].
As you guessed, the interaural coherence is not a major cue for distance perception, especially for greater distances, see [1].
sources:
1 http://www.acoustics.org/press/160th/lavandier.html
2 http://www.mendeley.com/research/assessing-auditory-distance-perception-using-virtual-acoustics/