Hi Eric,
On 4 June 2012 05:57, Eric Carmichel <[email protected]> wrote: > Hi Robert, > Thanks for the note. I remember a communication we had sometime back. > I agree that we cannot know what reality is like for another person. > Fortunately, inferential statistics, or just a plain ol' consensus, helps > here. For example, most normal hearing listeners get the sense (or illusion) > of a phantom images when listening to a decent stereo system. There's > agreement to this despite not knowing what each individual's perception is > like. But the same *illusion* may not apply to the hearing impaired listener. It does depend just what you mean by an "illusion". Within limits, some forms of stereo are not illusions - by that I mean that what is presented to the ears (or the CI's) is close enough to physically correct to not count (at least for me) as a true illusion. For a listener in the sweetspot, looking forwards, Blumlein Stereo produces wavefronts that have essentially the correct delays for ITD's to work - in the range where they are appropriate, i.e. low to mid. Properly implemented (i.e. matched HRTF's) headtracked binaural is even better, except for the lower bass where body resonances play a part. At the exact centre spot, Ambisonics recreates things fully - so is this an illusion? In practise, possibly yes, as it doesn't do as well away from that spot. WFS theoretically can recreate fully, even over an area, but practical limitations mean that it doesn't. For me, the only form of stereo that truly counts as illusory (albeit often highly enjoyable) is pure spaced pair. > But this isn't to say that hearing impaired individuals, or even those with a > profound unilateral hearing loss, can't localize/spatialize > sound. So, in > this somewhat elementary example, we could surmise that stereo recordings > would be a poor way of bringing > *physical reality* to the laboratory (unless it's stereo imaging techniques > we wish to evaluate). Absolutely on the last! > > Whether a person is studying auditory processing disorders, hearing loss, > implantable prostheses, vision, etc. it would be most ideal to have a > controlled, real-world environment. If the physical variable is both > *real-world* (for external validity) and repeatable / portable across > laboratories (latter being easy to do with recordings and modern > electronics), then the perceptual consequence of changes made to a single > variable (e.g. a change in a CI processor's envelope detector) can be > determined with a certain degree of confidence. Naturally there will be > outliers, a range, and all the stuff you know about much better than I do, > but I believe a *physically real* periphonic system will yield much more > meaningful results than a two speaker system in a tiny audiometric test > booth. In the early days of CI testing this may have not been the case: > Simply getting a decent speech understanding score was an accomplishment! But > as processors and hearing aids > advance, I believe the test protocols will have to advance too. Just my > thoughts here. Okay, so how about this? An anechoic environment, with standardised HOA speaker array to handle the early reflections and reverberation, which we can probably assume are more tolerant of deviations from physical reality, with the direct sounds actually coming from individual speakers - so exactly physically correct? Dave -- These are my own views and may or may not be shared by my employer Dave Malham Music Research Centre Department of Music The University of York Heslington York YO10 5DD UK Phone 01904 322448 Fax 01904 322450 'Ambisonics - Component Imaging for Audio' _______________________________________________ Sursound mailing list [email protected] https://mail.music.vt.edu/mailman/listinfo/sursound
