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Sorry about that.

It gets difficult keeping track of which forum I put stuff on. I will give a small primer for what I am talking about..please forgive me if you already know this stuff.

A re-mapping of a space is like matrix multiplication. Consider the re-mapping of space, from x,y coordinates to r, phi. Put x,y into the mapping function, get out a radial distance and an angle.. the remap function is a simple 2 by 2 array.

Consider a source of sound that emits a simple impulse like a click. (this is only for clarity of explanation). I also refer to an x-y coordinate grid, like a holodeck with the stripes on the floor.

Put that source 100 inches in front (y axis) and 20 inches to the right (x axis).

The click reaches the right ear about 80 uSec before the left.(this is ITD). The click intensity will be about .1dB louder in the right ear also (this is IID). (The assumption is that of a point source in space, the IID numbers will change for a line source, and will be a constant for a planar one nearfield.)

Now, move the source to the right 6 more inches. The ITD has changed approximately 6 uSec. And the IID has changed about .006 dB. (rough numbers, I'm looking at two graphs.)

If you can detect that move in space, you have at least a threshold for those parameters to that level. But .006dB is incredibly small, and most likely, far too small for us to detect. A quandry.

Most people will have great difficulty in noticing that shift in space. Not because they cannot detect it, but moreso because they don't have a solid reference to guage the shift with. But, if you have two coincident point sources and move one the 6 inches from the other, detection is easier.

This is called differential localization..the ability to distinguish a difference in space, as opposed to absolute localization.

Now, set your sound system up with an 11 band eq. Get a female vocal dead center, and increase the 10K slider on the right side only. If your eq changed only the level, then the sibilance of her voice will move to the right, leaving the rest of her voice still in the center..

Conversely, take MY speaker system with it's 5 and 10% tolerance crossover components, and try to visualize that same female vocal. Won't work, the sibilance is to the right..manu tolerances of course..but my eq can't move that vocal back correctly..can't get there from here..

What I am attempting to do with that eq, is trying to re-map the sibilance via the use of amplitude only adjustment, but that is not the only parameter that is incorrect in my speakers. Phase is off big time too.

Try playing a wave file on a comp card, where the output is multiplexed. One channel is 11 uSec leading the other. It is re-mapped, the imaging is all screwed up. My feeble attempts to move the image back to center by pan pot re-mapping, is useless. Now, the delay is still there, but the amplitudes are wrong..

So, now..Where in a that origional two dimensional grid, can I put a sound source, so that both ears hear the same volume, but one ear gets the signal 11 uSec before the other?? And, where in that grid can I put an object so that both ears get the information simultaneously, but it's louder in one ear??

Answer to both questions: You can't. Those places do not exist. The process has re-mapped the localization parameters, and our poor brain has to adapt.

Note that in my example, 6 uSec and .006 dB.. Those numbers are rather low, especially the .006dB. too low, we aren't that sensitive. But, we don't know how sensitive to differential localization as nobody's measured our ability correctly.

Can the selection of cable parameters alter the information (re-map) to those levels?? Of course, that can be measured. Can we detect it? Anecdotally, people say yes. Have we setup proper methods to test our ability..

No.

PS..I use the term mapping because win two d space, there are lines of constant ITD and lines of constant IID. Somewhat akin to a smith chart. Movement along a constant ITD line, like a pan pot does, is not a pure x or a pure y move, but rather, something different. Re-mapping is standard nomenclature, and is what I use for my motion control machines at work. It can be cumbersome to think about 11 dimension spacial movements..remapping is the easy way out.

Cheers, John


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