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On 01/07/2011 10:01 AM, Arnold Krille wrote:

quoted text
> On Friday 07 January 2011 09:10:41 Giso Grimm wrote:

>> On 01/07/2011 12:33 AM, fons@kokkinizita.net 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-

quoted text
> 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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