28 Feb
2010
28 Feb
'10
9:21 a.m.
disclaimer: this user is getting seriously confused.
On 02/28/2010 01:56 PM, fons(a)kokkinizita.net wrote:
To reproduce the field of a real source, you need
*all*
spatial harmonics, in theory (for a real point source)
up to infinite order. So An AMB system of order N must
not just recreate the harmonics up to order N, but *all*
of them. It will control some of them (but no more than
the number of speakers), and the rest has to be generated
by aliasing.
i can see how a soundfield mike would capture (and thus include in the
first-order signal)those aliased components, but then what about a
panner? following your argument, shouldn't we add higher-order aliased
components into a panner matrix?
A first order horizontal decoder with 4 speakers will
exactly control the levels of the 0, 1st and 2nd order
components, and the rest is filled in by spatial aliasing.
The aliased components are not exact of course, and that's
why localisation will be impaired if you move away from
the sweet spot.
Now if you use e.g. 8 speakers to reproduce horizontal first
order the system controls components up to 4th order. If the
input is just first order, the 2nd and 3rd order components
will be zero, as will be all those that alias from them (5,6,
10,11,13,14, etc.) The result is a field that does not match
well to that of a real source.
hmm. i still don't see from this explanation why 1st order horizontal
sounds worse over 8 speakers (or 12, for the sake of argument) than over
just six, even if i'm in the sweet spot.
best,
jörn
(who is about to crack open a can of fizzy InstaMath(tm) extra-strong)