Dave Hunt wrote:
It is true that 1st order ambisonics doesn't consider distance, with
all sources being reproduced at the distance of the speakers,
although Gerzon did consider distance panning. A Soundfield mic
recording contains distance information. If attempting spatial
synthesis, the ambisonic encoding equations do not include distance,
and this has to be added in various ways: amplitude variation
(inverse square or other law), hf air absorption, early reflections
and reverberation in a virtual space, source directivity, occluding
objects etc..
Sources inside the speaker distance cannot be be correctly
represented with 1st order ambisonics, as the x,y,z components all
diminish to zero at the listeners position, and this can be
compensated to some extent by increasing W to maintain a similar
loudness. As far as I can see, higher order components also tend
towards zero (apart from R, which tends towards a constant of -0.5).
Modelling near sources in HOA seems to depend mostly on the
'proximity effect': an increase of gain at low frequencies in the
directional components.
I'm not sure that this is really 'gimmickry' as Jörn suggests.
Hi...
I would highly suspect that some 3D audio game engines (Codemasters, for
example "DiRT" series) are considering distance cues. Although I don't
know this, I believe this would add a lot to a more realistic game
impression.
The fact that many people don't consider distance as some important
parameter doesn't mean it is a "gimmick", agreed.
Thanks for the clarifications!
Stefan
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