Re: [Sursound] Doppler ILLUSION (vs. shift) and more

[Bo-Erik Sandholm]

 
You are setting a hard goal for your self.
You also need to have a look at at the speakers that you are using,
not many speakers are able to recreate a waveform at a the listening position. 
It will definetely be a big challenge when using more than one speaker.
But maybe this is the first point you will have to overlook, Ambisonics at 
least tries :-).

- Bo-Erik

-Original Message-
From: sursound-boun...@music.vt.edu [mailto:sursound-boun...@music.vt.edu] On 
Behalf Of Eric Carmichel
Sent: den 31 maj 2012 20:57
To: sursound@music.vt.edu
Subject: [Sursound] Doppler ILLUSION (vs. shift) and more

- Part of original message removed here

If the system is REAL enough (again, referring to physical replication, not 
perceptual illusion), then iterations of the recording made through the system 
should yield recordings with identical, physically measurable attributes. By 
the way, thanks Dave for sharing insight and experience regarding your 
recording of a recording. I have access to a fairly large, semi-anechoic room 
(all walls, floor and ceiling well treated) that could be useful for such an 
experiment. I'll keep you posted.

As always, I greatly appreciate everyone's help and insight!
Best always,
Eric
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Re: [Sursound] Doppler ILLUSION (vs. shift) and more

[Eric Carmichel]

Greetings,
I very much agree with Bo-Erik that what I proposed would be a difficult, if 
not nearly impossible goal to achieve. Loudspeakers are certainly one of the 
weak links in the system--and the link most open to subjective impressions. Dr. 
Bengt-Inge Dalenbäck (CATT-Acoustic) had suggested using the Tannoy System 600 
near-field monitors (a great choice for my budget). I have a few of these, and 
saving for more. At present, I’m using older, passive KRK monitors with Focal 
drivers; I’ve matched the dozen or so I own for frequency response. The KRKs 
are fairly compact, yet each speaker has enough of a low end response that it 
can provide the requisite stimulus without need of a sub or second loudspeaker. 
Note: Some stimuli are designed to originate from a single location, hence the 
need for speakers that are independently full-range.
It’s probably a lot more reasonable to state that what I wish to achieve is a 
system that is “close enough” to a real world (acoustic) environment so that my 
listening experiments have external validity. Experiments that purport 
significant improvement in hearing aid or cochlear implant performance won’t 
mean much if (for example) noise is coming from one loudspeaker and a single 
talker (target stimulus) is emanating from a second speaker on the opposite 
side of the listener. This, to me, just isn’t “real world.” I’ve investigate 
several surround systems and I’m very pleased with results I get from my 
Ambisonics set up and recordings made with my TetraMic (in addition to more 
musical recordings made by many of you on the sursound list). Of course, my 
subjective impression of my personal system would hardly pass scientific 
scrutiny without measurable claims. Fortunately, nobody would expect a perfect 
system, but I should have a
 measurably “realistic” system if I’m going to denounce or applaud a new CI or 
HA processing strategy.
When it comes to sound source localization, I received a very kind email from 
Dr. WilliamYost the other day. Bill is undoubtedly one of the great names in 
psychoacoustics. The note below (from Bill) may be of interest to those 
interested in spatial hearing, ecological psychology (previous posts), and 
hearing in general: 
“I have been struck with how little we actually know about free-field sound 
source localization. My [Air Force] grant, which just started, deals with 
gaining more information about localizing more than one sound source, esp. when 
the sources produce sound at the same time. This is a topic with almost no 
literature... I am very interested in how the auditory system deals with 
situations in which the source moves and the listener is stationary as opposed 
to when the listener moves and the source is stationary. Both can produce 
nearly identical changes in cues like ITDs and ILDs, but it would not be good 
if the source was perceived as moving when the listener moves. There is a long 
and rich literature on this problem in vision, with several known neural 
circuits that cancel the retinal image changes based on vestibular or 
proprioceptive cues when the observer moves. There is very little work on this 
topic in the hearing literature.” [end abridged email]
As always, I am grateful for the help and insights that I receive on this 
mailing list and other sources. Fortunately, I’m also spending a lot of time 
making live (studio) recordings behind an SSL 4000 console, so my audio 
endeavors continue to be more play than work. Life is good.
Best always,
Eric
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[Sursound] Doppler ILLUSION (vs. shift) and more

[Eric Carmichel]

Greetings All,
Many thanks for the insightful responses to my recent post (Catching the same 
fly twice). I was pleased to read that most folks on the mailing list are a lot 
more qualified to discuss Ecological Psychology than I was (and thanks to E. 
Deleflie for the kind and insightful note).

Dr. Peter Lennox brought up a point that I had considered adding to my post. 
The point has to do with what spatial perception is/does. I very much agree 
that discerning or sensing a CHANGE in distance is more important than static, 
directional localization. This, too, can be intertwined with Gibson’s (and 
others) papers on point-of-impact, although Ecological Psychology deals more 
with vision that hearing. I will, however, unabashedly reveal that I received a 
D on high-school physics project because I wrote that the Doppler shift was 
mostly bogus when it comes to discerning motion (towards or away from the 
observer) because the Doppler shift yields a CONSTANT pitch shift until the 
point where it passes the observer. Years later, a paper was published by 
Michael McBeath (pronounced McBeth, as he told me) et al that proved that my 
earlier and ‘naive’ notion was correct.

McBeath wrote: ‘Despite this fact of physics [re Doppler shift], most people 
tend to hear a pitch rise as the train approaches and a pitch fall as the train 
departs... We tested this phenomenon in the laboratory by presenting listeners 
with simulated Doppler shifted tones and asking them to track with a joystick 
the changes in pitch that they heard... Since the physical measurement of 
frequency and the perceptual experience of frequency (i.e. pitch) were going in 
opposite directions, we called this phenomenon the Doppler illusion. The 
pattern of pitch change that is heard (rising then falling) resembles the 
pattern of LOUDNESS change that occurs. We argue then that the Doppler illusion 
is due to the change in loudness that occurs as the train approaches. More 
generally, dynamic changes in loudness can influence perceived pitch in a 
previously undocumented way.’ [Source = 
http://www.acoustics.org/press/133rd/4pppa3.html]

A lot of my research questions aren’t what the normal-hearing listener 
perceives, but what the hearing-impaired listener perceives. Sadly, we can't 
put ourselves in these shoes, even with simulations. It is for this reason that 
I wish to create a PHYSICAL replica of the acoustic environment, not merely an 
illusion that is 'real' to normal-hearing persons. Dr. Cynthia Comptom-Conley 
(Gallaudet University) did her dissertation on an 8-speaker surround system 
that was (originally) intended to be useful for audiologists. She demonstrated 
that hearing aid users made the same number and TYPE of mistakes in the 
surround environment as they did in similar, real-world environments. This, 
then, ‘proved’ that the surround system accurately replicated the real world. I 
know the system’s designer, and had recommended incorporating additional 
stimuli to extend the usefulness of the system. The designer frowned on 
Ambisonics, stating that recordings made with a
 Soundfield mic sounded muddy (Egad!! Did I mention he had hearing loss and 
wore hearing aids?). The sole recording for the research-oriented surround 
system was made with 8 Sennheiser gradient mics, each equally spaced in a 
horizontal array. Photos of this recording system show a KEMAR centered in the 
mics, but I learned that the photo was all for show (KEMAR really was being 
used as a dummy--to impress other dummies??). The system is novel and useful 
because it fits in a standard audiometric test booth, but I believe an 
Ambisonics system would be a lot more flexible (not to mention it's easier to 
make field recordings with a Soundfield mic).

Saying that HA users make the same mistakes in an artificial environment 
doesn’t really 'prove' that this environment provides the same sensation to 
hearing impaired people as a natural environment would, but the results 
certainly lend credence to the system, at least to the extent that one can 
demonstrate that directional mics are beneficial to hearing aid users. So, akin 
to gamers who are fooled by illusions, or normal hearing people who make 
mistakes when presented with distorted stimuli (to simulate hearing loss), my 
quest for the elusive Holy Grail of audio reality is to build a system that 
provides the same PHYSICAL pressures, wavefront curvatures and directions, 
phase angles, blah blah that existed at the recording site. Hopefully, too, the 
‘sweet spot’ would be large enough to permit normal head movement--the use of a 
bite brace just isn’t natural (the aforementioned system has a radius of 2 
feet, so head movements are frowned upon). From
 what I've read, acoustic holography, wave field reconstruction, or high-order 
Ambisonics are my best bets towards achieving this lofty goal.


If the system is REAL enough (again, referring to physical replication, not 
perceptual illusion), then itera