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In Reply to: RE: Early reflections and comb filters posted by Ethan Winer on December 13, 2007 at 14:31:16
Ethan,
>I've tried absorption, diffusion, and nothing at the side-wall first reflection points. Absorption won hands down. <
While this is fine in itself it hardly qualifies as experiment that shows that reflections generate audible comb filter coloration.
In his paper “Coloration and binaural decoloration in natural environments”, Acustica/acta acustica 2001, vol. 87, p.400 Brüggen writes that
"threshold data do not describe the percept of audible reflections, that is, what multidimensional perceptual changes occur when reflections are above threshold”
and
“reflections might be clearly audible but not perceived as disturbing”
This paper describes the only attempt I known of where music has been used for coloration/decoloration experiments and the experiment has been abandoned!
When designing coloration experiments one has to be very careful that the test subjects judge coloration and not change in spatial impression. Simply placing absorbers or diffusers to find that "absorption won hands down" just won't do it!
>If you want hard evidence in the form of graphs, see Figure 1 in THIS article on the RealTraps web site. The horribly skewed response from untamed early reflections is undeniable!<
I know these graphs, you have used a single mike and some test signals, I presume? Humans have two ears to beginn with and what's more, there's a head between these ears so using two mikes instead of one won't get you any further. If you used a dummmy head with mikes placed inside the ear canals you would get more meaningful results. And even in that case, two mikes on a dummy head do not process the sound waves like human hearing does. And even if they did, you are using test tones not music. While comb filter coloration is easily audible with test tones, there us no evidence that it is audible with music (cf. Brüggen).
Klaus
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