On 01/07/2011 10:01 AM, Arnold Krille wrote:
> On Friday 07 January 2011 09:10:41 Giso Grimm wrote:
>> On 01/07/2011 12:33 AM, fons@email-addr-hidden wrote:
>>> Azim and elev are in radians, to convert to degrees multiply by
>>> 180/pi. Note that for all layouts on the demon page, dist will
>>> be 1 for all speakers. For ambdec you should use the real distance.
>>
>> in ambdec, is the distance used for anything else then delay and gain
>> compensation? Is it correct that for regular setups this does not matter?
>
> I imagine it could be used:
> Ambisonic when shipped seems to be normalized to distance of 1 unit.
> When your speaker array is much bigger or smaller, one could use that
> information to rescale the sound reproduction.
> But I haven't actually thought about this or even tried some formulas... Might
> not work.
i guess you are hinting at jerome daniel's thoughts on near-field
compensation? i guess his point was that you have to assume a "standard"
distance when encoding, and the decoding would be wrong if your diameter
is different. however, as you say, since the decoder knows the assumed
standard, it can correct accordingly.
for those non-ambiheads wishing to follow this discussion:
the near-field effect in ambisonics results in a bass boost. it's caused
by the speakers. ambisonic theory (without NFC) assumes plane waves,
i.e. speakers that are very far away, so that the wave fronts are not
curved. since they are curved in practice, you get the bass boost. the
same thing is responsible for the well-known proximity effect on
directional microphones.
> Finally, one of the main advantages of ambisonics compared to that 5.1/7.1-
> crap is that your setup doesn't have to be perfect. Different distances and
> even different irregularities in shape can be compensated and still reproduce
> the signal as intended.
well, yes and no. the failure modes are different, too. depending on how
5.1 and 7.1 are mixed, you can usually place the speakers any old way
and still get something out of it, only the source positions will be
displaced. heck, ever seen those setups with all 5 speakers below the
screen, sitting on top of the vcr? not much surround, but you still get
the idea of the mix.
in ambi, it tends to work well for minor displacements (which you can of
course also correct in the decoder, but i'm assuming user errror here),
but for large uncompensated placement errors, the whole reconstruction
will fail. in this latter case, ambi will behave far less predictable
than any discrete speaker technique.
and people should not expect wonders from ambi rigs. the ITU 5.1 setup
is the most irregular you should try - anything worse than that, and
ambisonics won't be much fun.
maybe when franz zotter and his friends from graz get their partial
spheres decoder into a usable shape (right now it's pd magic only).
it basically enables you to build only parts of a loudspeaker sphere and
discard all direct sound coming from the wrong directions.
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Received on Fri Jan 7 12:15:04 2011
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