<div class="gmail_quote">On Sat, Apr 24, 2010 at 7:50 PM, nescivi <<a href="mailto:nescivi@gmail.com">nescivi@gmail.com</a>> wrote:<br>> yes, and in fact for higher frequency signals it is generally understood in<br>
> psycho-acoustics that we distinguish location more by level differences (due<br>> to masking of the head) than by phase differences, as the latter have become<br>> quite irrelevant, as the wavelength of these higher frequency is generally<br>
> much smaller than our ears are apart from each other. OTOH, the high frequency<br>> waves have a harder time bending around our heads, and thus create level<br>> differences based on whether the sound source is to the left or right of us.<br>
<br>Thank you for providing some useful perspective and attitude. (Is this your work? <a href="http://www.aes.org/events/122/papers/session.cfm?code=P5">http://www.aes.org/events/122/papers/session.cfm?code=P5</a> "Reproduction of Arbitrarily Shaped Sound Sources with Wave Field Synthesis—Physical and Perceptual Effects" -- Very interesting!!)</div>
<div class="gmail_quote"><br>What is the frequency at which these diffraction level effects produce level differences in the ears?? Are the results taken from <a href="http://www.aes.org/e-lib/browse.cfm?elib=14003">http://www.aes.org/e-lib/browse.cfm?elib=14003</a> ? (The Effect of Head Diffraction on Stereo Localization in the Mid-Frequency Range—Eric Benjamin, Phil Brown, Dolby Laboratories - San Francisco, CA, USA) -- IMHO, that paper explicitly focused on the mid-frequency range -- doesn't mean that is the extent of our hearing, nor is it clear they deny high-frequency effects, as they'd be in contradiction to a huge body of academic literature that states the exact contrary. Further, by limiting to "stereo localization" and mid-range they're implicitly ignoring pinna effects and throwing their experimental results in the direction they planned to prove in the first place: which is pretty obvious basic mixing -- you can use a pan-pot to place a midrange source in a stereo field. Also, i very much doubt they did they experiments to the same standards demanded by academic psychology research -- are their findings Post hoc ergo propter hoc scientific justification for existing product features or limitations? Has anybody in psychology accepted their findings as valid? Or reproduced the results independent of Dolby's financial interests?? </div>
<div class="gmail_quote"><br></div><div class="gmail_quote"><div>The part that doesn't make sense is that we can also localize sound up/down/front/back and certainly for up/down, level differences between the ears couldn't explain our ability to localize -- pinnae and high-frequency response does. Which is what the animal and perception psychology literature tells us. Fortunately, there *ARE* animal studies very similar to the ones i suggested we do, before declaring -- apriori -- what sound matters and what sound doesn't.</div>
<div><br></div><div>One thing you might find interesting is that there is at least counterargument to your statement for mammals -- with a 33khz hearing limit, requiring 40Khz bandwidth, and performing worse on a sound localization task as the bandwidth reduces under 20Khz: "like humans, chinchillas use the upper octave of their hearing range for sound localization using pinna cues." And yet we allocate very little resolution, at 44.1Ksamples/second, to hearing from which we derive positional cueues: "In humans, frequencies as high as 15 kHz have been shown to be necessary either for optimal discrimination in the lateral field or in elevation (Hebrank and Wright, 1974; Belendiuk and Butler, 1975). As the 60-dB upper limit of human hearing is at most 20 kHz, this means that the</div>
highest octave of the human hearing range is used to derive pinna locus cues."<div><br></div><div><a href="http://linkinghub.elsevier.com/retrieve/pii/S0960982209011701">http://linkinghub.elsevier.com/retrieve/pii/S0960982209011701</a></div>
<div>Sound localization in chinchillas. II. Front/back and vertical localization</div><div>Rickye S. Heffner *, Henry E. Heffner, Gimseong Koay</div><div> </div><div>...</div><div><br></div>
Effect of low-pass filtering<br> <br>The role of high frequencies in discriminations of eleva-<br>tion was systematically explored by determining the ability<br>of chinchillas to localize the 4 different low-pass signals<br>
presented from two speakers located 45 ° apart, again an<br>angle chosen for its moderate difficulty. As shown in Fig.<br>6, the performance of the 2 animals declined steadily,<br>reaching the 50% discrimination level at the 10-kHz low-<br>
pass setting and falling to chance at the 5-kHz setting.<br> To determine the effect of increasing the angle of<br>separation on performance, chinchilla P was also tested at<br>an elevation of 75 ° . As shown in Fig. 6, increasing the<br>
angle of separation resulted in only a small increase in<br>overall performance at the 40-kHz setting, but a much<br>larger increase at the lower filter settings. As at the 45 °<br>separation, performance declined steadily as the high-<br>
frequency content of the signal was reduced, although the<br>degree of the decline was not as great. Thus the impor-<br>tance of high frequencies for vertical localization can be<br>demonstrated at either angle. However, the size of the<br>
effect and the low-pass filter setting at which performance<br>falls to chance is dependent on the angle of separation.<br>...</div><div class="gmail_quote"><br> For comparison with the results of the two previous<br> left/right localization. Testing was conducted at 30 ° sepa-<br>
ration, the smallest angle supporting sustained performance<br> of approximately 80% and was thus of comparable diffi-<br> culty to the angles used in the tests of front/back and<br> elevation localization.</div><div class="gmail_quote">
<br></div><div class="gmail_quote">Fig. 7 shows that there was little difference in the ability </div><div class="gmail_quote">of the chinchillas to localize the broadband (i.e., the<br>40-kHz low-pass signal) and the filtered stimuli. Although</div>
<div class="gmail_quote">performance declined slightly with the 5-kHz low-pass<br>noise, there was no systematic reduction in performance as<br>seen in the two previous tests (cf., Fig. 7 with Figs. 4 and<br>6). Thus, it appears that chinchillas do not require the<br>
presence of high frequencies to perform a left~right<br>sound-localization discrimination, a result which suggests<br>that the binaural time cue is adequate to maintain their<br>level of acuity in this task. This point is discussed in more<br>
detail below.<br>..........<br><br></div><div class="gmail_quote">4.3. Role of high frequencies</div><div class="gmail_quote"><br> In order to be effective, pinna cues require the presence<br>of high frequencies in the signal to be localized. In hu-<br>
mans, frequencies as high as 15 kHz have been shown to<br>be necessary either for optimal discrimination in the lateral<br>field or in elevation (Hebrank and Wright, 1974; Be-<br>lendiuk and Butler, 1975). As the 60-dB upper limit of<br>
human hearing is at most 20 kHz, this means that the<br>highest octave of the human hearing range is used to<br>derive pinna locus cues.<br><br></div><div class="gmail_quote"> Like humans, chinchillas require high frequencies to<br>
localize sound using pinna cues. The results of both the<br>f r o n t / b a c k and vertical localization tests demonstrate that<br>performance declines as high frequencies are removed<br>from the signal and eventually falls to chance (Figs. 3, 4<br>
and 6). The range of frequencies necessary for pinna cues<br>to be effective depends, o f course, on the angle of separa-<br>tion (cf., Fig. 6). In order to perform consistently at 50%<br>or better at the angles of separation used here, vertical<br>
localization requires frequencies o f 10 kHz or higher<br>whereas f r o n t / b a c k localization requires frequencies of 5<br>kHz or higher (cf., Figs. 4 and 6). It should be noted that<br>performance in both tasks improved as higher frequencies<br>
were added to the signal, even for the addition of frequen-<br>cies above 20 kHz. As the 60-dB upper hearing limit of the<br>chinchilla is 33 kHz (Heffner and Heffner, 1991), this<br>suggests that, like humans, chinchillas use the upper oc-<br>
tave of their hearing range for sound localization using<br>pinna cues.</div><div class="gmail_quote"><br>4.4. Implications for the evolution of high-frequency hearing</div><div class="gmail_quote"><br>A m o n g vertebrates, mammals are unique in possessing<br>
good high-frequency hearing, i.e., the ability to hear above<br> 10 kHz. Some time ago it was suggested that the selective<br>advantage of mammalian high-frequency hearing is to<br>enable even small mammals to make use of binaural<br>
spectral-difference cues to localize sound (Masterton et al.,<br>1969). That is, interaural spectral-difference cues are avail-<br>able to an animal as long as it can hear frequencies with a<br>wavelength short enough to be shadowed by its small head<br>
and pinnae. This view is supported by research that has<br>shown that acuity for left/right sound localization in rats<br>and mice is decreased when high frequencies are filtered<br>out (Heffner, 1989; Mooney, 1992; Heffner and Donnal,<br>
1993).</div><div class="gmail_quote"><br> Over time it has become apparent that not all mammals<br>need high frequencies for optimum acuity for left/right<br>localization (Heffner and Heffner, 1992). For example,<br>frontal locus acuity in humans is not adversely affected by<br>
the removal of high frequencies from an acoustic signal<br>because the time cues available in the low-frequency por-<br>tion of the signal provide sufficient locus information<br>(Musicant and Butler, 1984). Similarly, left/right localiza-<br>
tion acuity in horses is not significantly affected by re-<br>moval of high frequencies and, indeed, there is evidence<br>that horses have lost the ability to use the binaural spectral<br>difference cue (Heffner and Heffner, 1986,1988c).<br>
As with humans, the ability of chinchillas to perform a<br>left/right localization discrimination is not affected by the<br>filtering out of high frequencies (Heffner et al., 1994). It<br>should be noted that this finding does not mean that<br>
chinchillas do not use the binaural spectral-difference cue.<br>On the contrary, their ability to localize high-frequency<br>tones demonstrates that they readily use binaural<br>intensity-difference cues and, presumably, the spectral-dif-<br>
ference cue (Heffner et al., 1994). However, it does<br>demonstrate that their frontal locus acuity can be sustained<br>by the binaural time cue alone. Thus, for chinchillas, the<br>primary selective advantage of high-frequency hearing may<br>
be to enable them to use binaural spectral cues a n d / o r<br>pinna cues to localize sound sources located away from the<br>midline and to make vertical locus judgements. Accord-<br>ingly, we might conclude that the appearance of pinnae<br>
accompanied by an extension of the high-frequency hear-<br>ing range combined to improve the sound localization<br>ability o f mammals within the lateral and vertical auditory<br>fields. Thus it is not surprising that the only bird known to<br>
have good acuity throughout auditory space is the barn<br>owl, an animal which has evolved a pinna-like structure<br>and has pushed its upper limit of hearing to just over 12<br>kHz, higher than that of most birds (Knudsen, 1980;<br>
Konishi, 1993).</div><div class="gmail_quote"><br><div>-------------------</div><div><br></div><div>-- Niels</div><div><a href="http://nielsmayer.com">http://nielsmayer.com</a></div></div>