On 06/17/2013 11:22 PM, Sampo Syreeni wrote:
On 2013-06-17, Jörn Nettingsmeier wrote
that's the main problem with the eigenmike: the higher the order, the
narrower the bandwidth and the higher the lower boundary. which means
that an eigenmike signal set will not usually be downwards-compatible
- if you aim for a correct amplitude response for the full 4th order
set, it will sound duller and duller the more orders you truncate. it
is possible to generate a spectrally correct output for each subset of
orders, but that has to be computed from the a-format, with a priori
knowledge of the playback order.
How does that happen? Okay, it might be that the usable frequency range
changes, but once you've done equalizing in the A to B step, don't you
then always get just a B-format set which you then decode at your target
order?
deriving low-frequency, high-order information from tightly packed
capsules (i.e. capsule distance small compared to wavelength) requires
ridiculous amounts of gain. at some point, you will only be amplifying
random noise, without any meaningful results. so it is important to
limit the lower boundary of a high order signal set.
the nice thing about this is that low orders alone are fine for low
frequencies (they provide a large sweet spot at LF), and higher orders
are only really needed to extend the sweet spot at HF.
so in theory, a setup like the eigenmike has quite useful
characteristics. as it stands today, the big problem is that this
bandlimiting effectively kills the biggest advantage of ambisonics, to
let the listener/consumer decide the playback order.
sure, for a separated eigenmike signal set, the necessary corrections
can be made for arbitrarily low orders, but as soon as you have panned
higher order sounds in your b-format master, it gets messy to the point
that i don't want to go there...
the same problem arises if you recklessly combine a POA microphone with
higher-order spots (like i'm guilty of), but the spectral issues are a
lot more manageable. plus it's way easier to keep a four-channel first
order signal set separate from the panned HOA set than a 32-ch
fourth-order eigenmike set.
--
Jörn Nettingsmeier
Lortzingstr. 11, 45128 Essen, Tel. +49 177 7937487
Meister für Veranstaltungstechnik (Bühne/Studio)
Tonmeister VDT
http://stackingdwarves.net
_______________________________________________
Sursound mailing list
Sursound@music.vt.edu
https://mail.music.vt.edu/mailman/listinfo/sursound
