Hi,
There are obviously severe limitations in trying to make signals
appear close to the listener with ambisonics. As far as I know, all
first and higher order spherical harmonics go to zero at zero
distance, the central listening position, leaving W (omni) only. The
ambisonic encoding equations do not inherently include distance, even
though they can be expressed in x,y,z coordinates, but only
direction. Distance is basically unity: sq(x) + sq(y) + sq(z) = 1.
We then have to resort to other methods of suggesting distance:
amplitude, arrival time of the sound from the source, the ratio of
direct to reverberant sound, high frequency absorption of sound from
distant sources (only really appreciable in free air beyond 50 to
100m), some sort of proximity effect leading to an increase in in the
level of low frequencies.
Some sounds have no immediately recognised source, and thus their
distance cannot be judged at all. If they move and the above factors
change, especially if they move past the listener, a meaningful
illusion can be created, as Dave has suggested. The Doppler effect
arises through the variation in the arrival time of the sound from
the source, and indicates the speed of movement of the source towards
or away from the listener.
WFS claims to offer a solution but, as pointed out, is "a lot of
speakers to lug around" and a lot of amplifiers, cable, audio
hardware and signal processing power. Then it's down to hybrid
solutions like Gus's " put a hidden speaker close to them and use Dbap".
If only we had loudspeakers that were invisible, weightless, required
no power or cable, could be moved and resized at will and be placed
anywhere without support, could be passed through by human beings
with no injury, and were capable of producing high quality sound at
any level, etc., we could do it using one speaker per sound source.
Ciao,
Dave Hunt
On 7 Nov 2014, at 17:00, sursound-requ...@music.vt.edu wrote:
From: Augustine Leudar <augustineleu...@gmail.com>
Date: 7 November 2014 16:18:08 GMT
To: Surround Sound discussion group <sursound@music.vt.edu>
Subject: Re: [Sursound] The "BUCKET LIST" for Ambisonics? - or only
how to proceed with Head tracked Binaural listening directivity
control ?
Hi Dave,
Is that the one that adds bass to the signals that come closer ? I
only ask
because I have never heard an ambisonics composition that
successfully made
the sound seem close to the listener which is weird because that's
what a
lot of people assumes it can do - and I have heard a lot of ambisonics
compositions in the Sonic lab which is is a 48 speaker array in an
acoustically pretty controlled environment by people from all over the
world. I've also read papers from Ircam where researchers claimed they
could get sounds to come a couple of metres inside the array
effectively
but no more - they almost blew up Ircams system apparently when the
bass of
the nearfield went out of control. Nonetheless its possible that the
artists involved didn't have access to the right software for
encoding such
NFC-HOA recordings - is there any software around with which I
could try it
out ? I would be interested in moving synthesised sounds around
with some
sort of panner rather than replaying recordings. I have had some
success at
this with ICSTs panner - as you say with fast moving sources - but
I put
this down to psychoacoustic effects rather than wavefront
shinanigans -
plus as somebody will no doubt point out this is ambisonics equivelant
pannin. . WFS of course but its a lot of speakers to lug around -
so for
the time being if I want a sound to seem likes its close to someone
I put a
hidden speaker close to them and use Dbap - I find ambisonics
useful for
surround sound panning as it seems to fill the holes better -
especially if
you can adjust the directivity. Anyway - Id love to give any NFC-HOA
software out there a test drive if there's any available,
all the best,
Gus
On 5 November 2014 03:47, Dave Malham <dave.mal...@york.ac.uk> wrote:
Hi there,
It depends what you want to do. If you can limit yourself to
fairly
rapidly moving sources, then you can get some way towards this
even in FOA
especially if the replay venue is reasonably dry and the acoustic
of the
soundscape is somewhat reverberant. With a bit of doppler, the
appropriate
variance of direct to reverberant field and patterns of early
reflections,
it will be difficult for the brains of the listeners not to
perceive the
source as moving past their heads (if that's the path you've set).
However,
the slower the rate of travel, the more likely it is to fall apart
and
revert to the source appearing to come from no closer than the reverb
radius (usually the surface of the speaker array). If you want to go
further, you need to use NFCHOA, (see Jerome Daniel's work).
Dave
On 5 November 2014 00:21, Augustine Leudar
<augustineleu...@gmail.com>
wrote:
I'm wondering - what is other artists experiences of using
ambisonics to
get sounds to appear "close" to the listener - ie proximity or in
WFS
focussed sources ?
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