Subject: Re: Acoustic Flow Field Generation From: Peter Lennox <peter(at)LENNOX01.FREESERVE.CO.UK> Date: Sun, 2 Sep 2001 10:26:56 +0100This is a multi-part message in MIME format. ------=_NextPart_000_002D_01C13399.CA6AE320 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Acoustic Flow Field GenerationThere are several issues here: 1) different mics are known to behave quite differently in 'reactive' = (ie enclosed or semi-enclosed)spaces (ref: Angelo Farina), and thus vary = in their abilities to reproduce the salient plane-wave characteristics. = Allthough the same mics are being used to record human speakers and = loudspeakers, which would seem to rule out this factor, because of the = ways that the two types of source may differ in their relationships with = local surfaces, this might still be pertinent. (in other words, you = could get some mics which yield similar results for both types of = source, theoretically). 2) Loudspeakers sound more like loudspeakers than they do anything else. = A given speaker's diffusion characteristic, and hence it's acoustic = relationships with local features remain fairly constant, irrespective = of programme material (to a point!). 3) A loudspeaker is (generally) designed to be part of a 'sound field = reproduction system', rather than as a sounding object in itself (with = the exception of speakers which are in fact designed to be part of a = musical instrument, such as guitar cabs - these could be called = 'production systems' rather than re-production systems). As such, a = design intention is to minimise resonances at all frequencies, whereas = all the 'sounding objects' the speaker is to imitate rely on resonance = for the majority of their energetic output. Because of acoustic coupling = (air-transformer) effects, an object in resonance interacts with it's = local environment quite differently from a sounding object which is not = in resonance. 4)In fact, from 3), an important design criterium for speaker enclosure = design is to minimise speaker -room interactions, inhibiting speaker = localiseability in favour of phantom image localiseability. It's my guess that the loudspeakers should be most localiseable when = they are a) distorting in one or more ways (compressing,clipping, = resonating etc.,) or b) playing material which is electronically = generated, and never in itself contained any 'spatial information' (with = apologies for using the term 'information' in this way). This highlights the problem with the (generally held) notion that it is = possible to accurately record 'a sound' yet strip it of any spatial = attribute - what is often called 'direct sound'.Consideration of what = might constitute 'direct sound' shows the term to be a theoretical = entity which is useful, but about as likely as a 'point source'. It is unclear whether the sense of moving through an environment that = you are after would be improved by better localisability of sounding = objects in that environment, or whether some other characteristic of the = environment itself might directly appeal to spatial perception in such a = way as to generate a sense of 'out there-ness'. (I suspect the latter). Lastly, from an ecological point of view, there's the question of = whether a highly symmetrical environment such as the corridor you = describe is particularly 'natural'; did we evolve best acuity for this = type of environment? I suspect not, and that a highly symmetrical = environment is second only to an anechoic one in terms of difficulties = in localisation. Reflections and resonances are simply too homogenous, = which is tantamount to saying 'lacking in potential-information' .(I've = done some informal experimenting in large circular empty spaces) The bottom line is, loudspeakers don't sound like 'real objects' (unless = they are actually being real objects). They actually imitate a wide = variety of real objects fairly well from the perspectives of considering = frequency response, dynamic range etc., but none of their design = criteria have anything to do with spatial perception. It would be interesting to speculate as to what conditions you would = need to achieve similar results for 'real' speakers and loudspeakers. regards, ppl ----- Original Message -----=20 From: Michael S. Gordon=20 To: AUDITORY(at)LISTS.MCGILL.CA=20 Sent: 29 August 2001 21:43 Subject: Acoustic Flow Field Generation Dear List - I am interested in capturing the acoustic flow field of a person = walking down a hallway. Thus far I have made a couple of binaural = recordings of (1) a perceiver walking past individuals reading text = (live) and (2) a perceiver walking past a series of loudspeakers = projecting an assortment of recorded sounds (e.g., human speech, = typewriter clicks, etc.). Those who have listened to these recordings = have found the first set a much more compelling indication of the = listener's motion than the second. There are several reasons why this = may have been the case: the live readers were fewer, more sparsely = located, and generally louder than the recordings via loudspeakers. I am writing to the list because I was hoping that some of you = might have some intuitions or know some references that would help guide = me to more successfully capture the acoustic flow field of a person = walking through a hallway. Specifically I am wondering whether live = sounds should be easier to localize through a loudspeaker than recorded = sounds? Furthermore should the localizability of the sound sources = contribute to the 'realness' of the walking event for a listener? I = would greatly appreciate any thoughts on this issue. Respectfully, Mike Gordon --=20 Michael S. Gordon Ecological Acoustics Laboratory Department of Psychology University of California, Riverside Riverside, CA 92521 USA 909-787-4579 mike.gordon(at)psych.ucr.edu = http://www.psych.ucr.edu/faculty/rosenblum/Mike_Gordon/MikeGordon_home.ht= ml=20 ------=_NextPart_000_002D_01C13399.CA6AE320 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD><TITLE>Acoustic Flow Field Generation</TITLE> <META http-equiv=3DContent-Type content=3D"text/html; = charset=3Diso-8859-1"> <META content=3D"MSHTML 5.50.4134.600" name=3DGENERATOR> <STYLE></STYLE> </HEAD> <BODY bgColor=3D#ffffff> <DIV><FONT size=3D2>There are several issues here:</FONT></DIV> <DIV><FONT size=3D2>1) different mics are known to behave quite = differently in=20 'reactive' (ie enclosed or semi-enclosed)spaces (ref: Angelo Farina), = and thus=20 vary in their abilities to reproduce the salient plane-wave = characteristics.=20 Allthough the same mics are being used to record human speakers and=20 loudspeakers, which would seem to rule out this factor, because of the = ways that=20 the two types of source may differ in their relationships with local = surfaces,=20 this might still be pertinent. (in other words, you could get some mics = which=20 yield similar results for both types of source, = theoretically).</FONT></DIV> <DIV><FONT size=3D2></FONT> </DIV> <DIV><FONT size=3D2>2) Loudspeakers sound more like loudspeakers than = they do=20 anything else. A given speaker's diffusion characteristic, and hence = it's=20 acoustic relationships with local features remain fairly constant, = irrespective=20 of programme material (to a point!).</FONT></DIV> <DIV><FONT size=3D2></FONT> </DIV> <DIV><FONT size=3D2>3) A loudspeaker is (generally) designed to be part = of a=20 'sound field reproduction system', rather than as a sounding object in = itself=20 (with the exception of speakers which are in fact designed to be part of = a=20 musical instrument, such as guitar cabs - these could be called = 'production=20 systems' rather than <EM>re-</EM>production systems). As such, a design=20 intention is to minimise resonances at all frequencies, whereas all the=20 'sounding objects' the speaker is to imitate <EM>rely</EM> on resonance = for the=20 majority of their energetic output. Because of acoustic coupling=20 (air-transformer) effects, an object in resonance interacts with it's = local=20 environment quite differently from a sounding object which is not in=20 resonance.</FONT></DIV> <DIV><FONT size=3D2></FONT> </DIV> <DIV><FONT size=3D2>4)In fact, from 3), an important design criterium = for speaker=20 enclosure design is to minimise speaker -room interactions, inhibiting = speaker=20 localiseability in favour of phantom image localiseability.</FONT></DIV> <DIV><FONT size=3D2></FONT> </DIV> <DIV><FONT size=3D2>It's my guess that the loudspeakers should be most=20 localiseable when they are a) distorting in one or more ways=20 (compressing,clipping, resonating etc.,) or b) playing material which is = electronically generated, and never in itself contained any 'spatial=20 information' (with apologies for using the term 'information' in this=20 way).</FONT></DIV> <DIV><FONT size=3D2></FONT> </DIV> <DIV><FONT size=3D2>This highlights the problem with the (generally = held) notion=20 that it is possible to accurately record 'a sound' yet strip it of any = spatial=20 attribute - what is often called 'direct sound'.Consideration of what = might=20 constitute 'direct sound' shows the term to be a theoretical entity = which is=20 useful, but about as likely as a 'point source'.</FONT></DIV> <DIV><FONT size=3D2></FONT> </DIV> <DIV><FONT size=3D2>It is unclear whether the sense of moving through an = environment that you are after would be improved by better = localisability of=20 sounding objects <EM>in</EM> that environment, or whether some other=20 characteristic of the environment itself might directly appeal to = spatial=20 perception in such a way as to generate a sense of 'out there-ness'. (I = suspect=20 the latter).</FONT></DIV> <DIV><FONT size=3D2></FONT> </DIV> <DIV><FONT size=3D2>Lastly, from an ecological point of view, there's = the question=20 of whether a highly symmetrical environment such as the corridor you = describe is=20 particularly 'natural'; did we evolve best acuity for this type of = environment?=20 I suspect not, and that a highly symmetrical environment is second only = to an=20 anechoic one in terms of difficulties in localisation. Reflections and=20 resonances are simply too homogenous, which is tantamount to saying = 'lacking in=20 potential-information' .(I've done some informal experimenting in large = circular=20 empty spaces)</FONT></DIV> <DIV><FONT size=3D2></FONT> </DIV> <DIV><FONT size=3D2>The bottom line is, loudspeakers don't sound like = 'real=20 objects' (unless they are actually <EM>being</EM> real objects). They = actually=20 imitate a wide variety of real objects fairly well from the perspectives = of=20 considering frequency response, dynamic range etc., but none of their = design=20 criteria have anything to do with spatial perception.</FONT></DIV> <DIV><FONT size=3D2></FONT> </DIV> <DIV><FONT size=3D2>It would be interesting to speculate as to what = conditions you=20 would need to achieve similar results for 'real' speakers and=20 loudspeakers.</FONT></DIV> <DIV><FONT size=3D2>regards,</FONT></DIV> <DIV><FONT size=3D2>ppl</FONT></DIV> <BLOCKQUOTE=20 style=3D"PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; = BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px"> <DIV style=3D"FONT: 10pt arial">----- Original Message ----- </DIV> <DIV=20 style=3D"BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: = black"><B>From:</B>=20 <A title=3Dmsgordon(at)CITRUS.UCR.EDU = href=3D"mailto:msgordon(at)CITRUS.UCR.EDU">Michael=20 S. Gordon</A> </DIV> <DIV style=3D"FONT: 10pt arial"><B>To:</B> <A = title=3DAUDITORY(at)LISTS.MCGILL.CA=20 href=3D"mailto:AUDITORY(at)LISTS.MCGILL.CA">AUDITORY(at)LISTS.MCGILL.CA</A> = </DIV> <DIV style=3D"FONT: 10pt arial"><B>Sent:</B> 29 August 2001 = 21:43</DIV> <DIV style=3D"FONT: 10pt arial"><B>Subject:</B> Acoustic Flow Field=20 Generation</DIV> <DIV><BR></DIV><FONT face=3D"Times New Roman">Dear List=20 -<BR> I am interested in capturing the acoustic = flow=20 field of a person walking down a hallway. Thus far I have made a = couple of=20 binaural recordings of (1) a perceiver walking past individuals = reading text=20 (live) and (2) a perceiver walking past a series of loudspeakers = projecting an=20 assortment of recorded sounds (e.g., human speech, typewriter clicks, = etc.).=20 Those who have listened to these recordings have found the first set a = much=20 more compelling indication of the listener’s motion than the = second. There are=20 several reasons why this may have been the case: the live readers were = fewer,=20 more sparsely located, and generally louder than the recordings via=20 loudspeakers.<BR> I am writing to the = list=20 because I was hoping that some of you might have some intuitions or = know some=20 references that would help guide me to more successfully capture the = acoustic=20 flow field of a person walking through a hallway. Specifically I am = wondering=20 whether live sounds should be easier to localize through a loudspeaker = than=20 recorded sounds? Furthermore should the localizability of the sound = sources=20 contribute to the ‘realness’ of the walking event for a = listener? I=20 would greatly appreciate any thoughts on this issue.<BR><BR></FONT> <BLOCKQUOTE><FONT=20 face=3D"Times New = Roman"> = Respectfully,<BR> &n= bsp; Mike=20 Gordon<BR></FONT></BLOCKQUOTE><FONT face=3D"Times New Roman">-- = <BR>Michael S.=20 Gordon<BR>Ecological Acoustics Laboratory<BR>Department of=20 Psychology<BR>University of California, Riverside<BR>Riverside, CA=20 = 92521<BR>USA<BR>909-787-4579<BR>mike.gordon(at)psych.ucr.edu<BR>http://www.p= sych.ucr.edu/faculty/rosenblum/Mike_Gordon/MikeGordon_home.html=20 <BR><BR></BLOCKQUOTE></FONT></BODY></HTML> ------=_NextPart_000_002D_01C13399.CA6AE320--