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Unknown transient/echo effect, Any idea what this is?
DickD
post Aug 19 2003, 21:44
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I recently heard an effect of hearing perception that I'm not sure I've known about before. Perhaps it's well known.

To paint the picture, I was recently rewiring a house (brick cavity wall external construction, brick or sometimes breezeblock internal walls) and putting in socket boxes and channelling the walls to bury the cables. I was using a cold chisel (metal), hitting it with a club hammer (also metal ended, with wooden handle) about 60-100 beats per minute, usually chipping away at red brick or mortar beneath the plaster surface layer on the walls to make fine adjustments to the holes made by the box-sinker or the channelling depth.

The rooms I was working on were fairly empty and echoey. Particularly when working near the corner of a room, when hammering the chisel repeatedly, I could make out the multiple closely-spaced echo transients after each impact transient. (around tens echoes per second, I'd guess)

However, when hitting just once, or listening for the closely-spaced echoes after the first hit, I was unable to discern the echoes, but they became audible on multiple repeated hits. This was different from hearing the resonant tone of a room (I found that in some other rooms) but I heard echo effect this when working in more than one location (though not all locations).

I'm aware of the principle of the ambiguity zone (the effect has a person's name, possibly van-Something - Dutch? - I don't have the source of that info on this PC) where echoes with a short enough delay are perceived as ambience that give cues to the environment, space and depth and 'belong' to the original sound and its original location, but delays significantly over about 40-50 ms are perceived as separate sounds as if they originate from another source, possibly elsewhere.

Is this some form of modification to the ambiguity delay, or some disturbance to temporal post masking from repeated transients? Or is it something to do with the loudness and the ear's protection mechanisms adapting to protect the ear once loud noise has been detected? Might it have something to do with the summer cold/influenza I'd just been recovering from (doubt it, as I've noticed it at many different occasions with different levels of symptoms)?

No rush to reply as I probably won't be online for a few days, but I wondered if anyone had any insight or suggestions to explain my perception. Obviously it's difficult to repeat without knocking seven bells out of the place, and I can't ABX it!

Cheers,

DickD
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Azeteg
post Aug 23 2003, 17:30
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Perhaps your rate of hitting the chisel was related to the size of the room, which could mean longer delays you could not hear first added up when hitting multiple times.

Or something.

/Azy
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