[Tech1] Topic for today Stereo vision

[Chris Woolf]

It is quite interesting that you were listening in the dark.  The 
longitudinal depth of a stereo image is a tricky thing to measure, but 
most research seems to find that it is very hard to persuade a mind to 
accept an image that is bigger than the room it is played back in. You 
can increase it in people's /imagination/ (with darkness or eyes closed 
helping that) but /location/ of instruments etc is very difficult to 
agree upon. This is much like spaced mic stereo - lovely effect, but a 
touch ethereal in detail. There's a big difference between an impressive 
imagined (subjective) image and a repeatable objective one.

With good WFS it does seem possible to overcome this limitation, mainly 
because you can move around. Since the "distant" images stay put when 
you move - something that can't happen with conventional stereo replay 
systems - your brain is prepared to accept the slightly confusing 
concept of sound beyond the visibly finite boundaries.

With headphones distance is equally confusing for the brain - hence the 
common problem of central forward sound often popping back into the 
middle or top of a listener's head. The brain has do a lot of imagining 
to project the image where it should be, and how well that happens 
varies a lot with individuals.

Where it /can/ work is if the audio is convolved with an accurate (and 
individual)  HTRF, and a fast head tracker. Once again, it seems that is 
because you can move around and the image still stays where it should be 
- locked to the world, and not to your body position - so your brain 
doesn't get too many challenges to correct for reality.

There's been fair bit of work on pilot's headphones, giving them 
"traffic" indications Done well, the warning can come from where the 
nearby aircraft actually is, making it much easier to find visually - 
but this has to be an objective positioning, not an imagined one.

Chris Woolf


On 10/10/2022 06:02, Keith Wicks wrote:
> I disagree that stereo sound has "a distance limit of no more than the 
> room dimensions." (I take that to mean the dimensions of the room in 
> which the sound is reproduced, not the room in which the sound was 
> recorded.) The first good quality stereo sound I heard was at Evesham 
> (1961), in an acoustically dead studio. The studio lights were turned 
> off during the demonstration, which featured a full symphony orchestra 
> in a fairly live hall. Afterwards, when the lights were turned on 
> again, it came as a great surprise to see how small the studio was, as 
> the recording had given the impression of being played in a concert 
> hall that was much larger than the studio used for the demonstration. 
> (Dave Mundy probably heard that demonstration too. I don't know 
> whether his experience was the same as mine. I have not asked.)
>
> On reflection, the effect of increased depth could be expected as the 
> depth of stereo sound produced by headphones is not limited either.
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://tech-ops.co.uk/pipermail/tech1_tech-ops.co.uk/attachments/20221010/61dc158e/attachment.html>