Dual 505 update
On Wed, 11 Mar 2015 10:57:34 +0000, Sumatriptan
wrote:
On 11/03/2015 09:12, Jim Lesurf wrote:
Yes, it has. See what others have now said, for example.
Also IIRC it is touted by at least one company as a way to 'throw' audio so
that it can be heard in one area but not others. The trick is to send one
set of ultrasonic tones from one speaker and another from a different
speaker. You then are said to only hear the intended intermod in the area
where the beams cross.
No idea how well it works. Only recall hearing reports about it. Must admit
my concern was the exposure to high levels of ultrasound and I wonder if it
would eventually damage hearing or cause some other problem.
Interesting result from Don in this thread. I didn't try it myself
because of worries about screaming high ultrasonics affecting my
hearing. So, the verdict seems to be that they can't be heard in
isolation but may impact perception of sound within the audible range.
Just wondering, does material outside the usual hearing range contribute
or detract from perceived 'realism' of recordings? Quite relevant
because we have a whole niche industry selling products offering
performance at at 20 kHz and above that may/may not be relevant to the
sound we can hear.
Of course, subsonics are an example of sounds that may not be heard but
are widely known to be perceived.
Yes, this all rather begs the question of _just_ how far we should go
in pursuit of 'perfect reproduction' of the original 'sonic
experience'. Do we (or even _should_ we) go so far as to risk hearing
damage by reproducing the full range of frequencies and SPLs or do we
make some reasonable compromise in this regard?
One excellent example of using a compromise to successfully emulate a
sonic experience is demonstrated in the "Wolfenstein 3D" 'demo' games
in regard of the pistol shots.
Firing a hand gun without ear defenders causes the ear's own AGC to
kick in in response to the initial high level transient after clipping
the 'crack' of the shot so that the ensuing reverberations and other
incidental noises become very muted, initially swiftly returning back
to more normal sensitivity levels in an exponential return to full
sensitivity.
Obviously, in a computer game, no sane game designer is going to ask
or even expect the serious gamer to invest in a KW rated PC speaker
system or use 10 watts per channel into efficient closed back
headphones to provide the 40 or 50 dB extra dynamic range to permit
the game player the 'full experience' of firing such a weapon under
combat conditions. However, what the clever game designer has done
here, is to impose a simulation of the ear's own dynamic sensitivity
response on the sound track's volume level curve so that what the
listener experiences (in a reasonably quiet environment free of other
sonic distractions that would otherwise 'give the game away') is very
close to the perception of the real experience but without imposing
any damaging stresses on the gameplayer's hearing.
I've no doubt the experience of fire arms enthusiasts were enlisted
to fine tune the simulation of the 'pistol shots' at least to the
point of eliminating unsoliicited criticism from those game players
who've actually fired such weaponery. It certainly met my expectations
of just how one would percieve such sounds, ignoring the physical pain
and damaging effects of the 'real thing'.
I have to say, it was this attention to detail that left a lasting
impression even though, by today's standards, the screen resolution
was ludicrously low (however, it was, at the time, the best resolution
in a "First Person '3D' Point and Shoot 'em up" game, mainly, it has
to be said, on account it was the _only_ "First Person '3D' Point and
Shoot 'em up" game available at that time :-)
The point I was making is that we don't necessarily want to reproduce
the whole of the audio spectrum of an original performance with such
extreme accuracy when very often all we really require is
verisimilitude.
Admittedly such processing to 'simulate' the dynamic effects of the
human ear can only be optimised for a small range of 'ideal' SPLs but
this hasn't stopped us fitting and using volume controls in the past
and to this day. Even extreme audiophiles will accept such compromises
as a necessary evil to accommodate the needs of others and also to
trade off reality against the need to preserve one's sense of hearing
for other novelties. IOW, the volume control is a tacit admission that
we're never going to achieve the Nirvana of sonic perfection (at least
not in this 'Plane of Existence'. :-)
I'm interested in Don's report of sudden onset of IM products. I wonder
where in the ear they are being generated...drum, stapes, cochlea,
brain? Plenty of scope for non linearity in that soft squidgy stuff we
are made from.
A lot of the 'overload' distortion arises in the the modified jaw
bones (stapes, hammer and anvil) when, just like a mistracking stylus,
they part company at their points of contact on sound pressure peaks.
It's actually possible to observe this type of 'in the ear'
distortion' when stood too close to the speakers at a rock music
performance by making the 'overload' distortion go away by the simple
expedient of plugging your ears with your fingers. The disappearance
of such 'clipping distortion' products has nothing to do with the LPF
effect associated with shoving a finger in each ear and more to do
with reducing the SPL at the ear drum.
The other sources of distortion in the cochlea and the central
nervous system become less quantifiable (in that order) but
undoubtedly exist. It's the very last part of the chain that's the
least quantifiable and hardest to understand (the cochlea is merely a
more subtle example of the mechanical problems demonstrated by the
three smallest bones in the human body).
Here we get ourselves into the realm of 'Psycho-acoustics' where a
dichotomy exists between our processing of sounds to allow us to
overcome interference effects in the environment in order to extract
the important 'information' that assisted our survival against other
threats as well as more recently, understand messages from fellow
members of our immediate tribe once our species had evolved into
co-operative hunter gatherer groups, a skill that finally evolved into
the one that lets us speak to each other, even under extremes of
interference. That same skill that allows us to appreciate the
'message' contained in 'musical works of art' ( that is, the ability
to enjoy a modern pop record despite the less than ideal listening
conditions :-).
The thing is, such 'signal processing' powers of the brain, can be
'reprogramed' by the mind contained within that brain. Indeed, such
'reprograming' is an ever continuing process during each individuals'
lifetime. It's a consequence of the 'adaptability through learning'
that gave our otherwise ill armoured, under-weaponised bodies the edge
over other 'better equipped' prey and predator species.
The consequence, of course being that we can choose to ignore
deficiencies in the whole audio system in order to concentrate on the
message in the music (including MP3 encoding/decoding errors) or else,
in looking for 'more detail' in the playing of more complex
orchestrations, find ourselves picking out the deficiencies of the
whole audio system.
Dedicated audio engineers, being engineers, like to define 'The
Problem' as simply as possible (hence the basic definition of working
over a range of frequencies limited to between 20 and 20000Hz with a
dynamic range of 90dB and almost zero distortion within that well
defined audio spectrum).
Such 'limits' are wide enough to satisfy all but a very few dedicated
Hi-Fi enthusiasts so dedicated in their pusuit of sonic Nirvana as to
be willing to take the risks involved in reproducing the more extreme
musical performances (the cannonade in Tchaikovsky's 1812 Overture,
anyone? see the comments for this you youtube example
https://www.youtube.com/watch?v=VbxgYlcNxE8 )
I'm currently listening to it as I type. I started with the volume
set at "Easy Listening Level" and it's at the 4 minute mark. I'll let
you know whether I agree with the comments in another eleven minutes
or so. :-)
The point is, I feel any such such 'Ultra Hi-Fi' system will need to
incorporate a mode switch marked "SOAR"[1] and "Ultra (risk of some
hearing loss)".
I've just finished auditioning that youtube rendition. Sadly, it was
a lttle disappointing since either the recording itself failed to
capture the dynamic range or the the streaming wasn't up to handling
the job. The cannon shots were obviously clipped with no sign of
psycho-acoustic processing as per the Wolfenstein 3D example of pistol
shots which so excellently dealt with the problem.
However, I have to admit I was only using a pair of PC speakers,
admittedly of above average quality and box volume, rather than
through my 50+50W RMS per channel (200W PMPO) mini power amp and large
speakers capable of rattling the otherwise unrattleable windows of the
downstairs lounge.
I suspect I'd have still heard the same shortcoming. There are so
many places in the transmission chain for such clipping effects to
manifest themselves, including the recording itself for which there
was no information as to its origin. Too many unknowns to fathom out
the cause for my sense of disappointment. :-(
[1] SOAR = "Safe Operating Area Restrictions applied"
--
J B Good
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