On 3/26/19 2:59 PM, Martin Dupras wrote:
Thank you for all the answers. I do appreciate.
However, no one has answered my question. I will ask again.
Can someone point me to any published resources that explain the principles
and theoretical equations required to in theory convert from 2nd order
A-format to B-format? I can find resources for 1st order but not for 2nd
order.
Hi Martin, see:
http://www.aes.org/e-lib/browse.cfm?elib=19682
"The *SpHEAR Project Update: The TinySpHEAR and Octathingy Soundfield
Microphones"
Has some details on the second order Ambisonics microphone calibration I
am doing for my 3d printed 8 capsule microphones (almost no theory, that
has been published before and the references might help, in particular
Eric Benjamin's original article for his 8 capsule design - which is the
one I implemented in the project). Contact me off-list if you don't have
access to AES...
-- Fernando
On Tue, 26 Mar 2019 at 21:54, Fons Adriaensen <f...@linuxaudio.org> wrote:
On Wed, Mar 27, 2019 at 04:50:06AM +0800, Stephen McArdle wrote:
I think the question might be more simpler than this.
For 1st order (with 4 microphones) the very first A to B
equations are (for example):
W' = FLU+FRD+BLD+BRU
X' = FLU+FRD-BLD-BRU
Y' = FLU-FRD+BLD-BRU
Z' = FLU-FRD-BLD+BRU
It's not that simple. This would work if
* your capsules are exactly hypercaridiod (i.e. max
directivity), independent of frequency, and
* they are *perfectly* matched.
That is not the case in practice. Even if the capsules
are high quality and well matched you will need some
EQ in addition to these simple sums.
What would the equations be for 8 microphones?
W' = FLU+FRD+BLD+BRU+FRU+FLD+BLU+BRD
X' = FLU+FRU+FRD+FLD-BLD-BRU-BLU-BRD
Y' = FLU+FLD+BLD+BLU-FRU-FRD-BRD-BRU
Z' = FLU+BRU+FRU+BLU-FLD-BLD-FRD-BRD
No, this is completely wrong, ignores all practical
aspects, and again it's not that simple.
But what about R’,S’,T’,U’ ??
Much more complex again.
In practice you can't do this to sufficient accuracy
without rather complex EQ or convolution.
And anyway, trying to do A/B conversion (or even Ambisonic
decoding) in environments like PureData, SuperCollider and
similar is a sure recipe for disaster. These are all
*artistic* tools, and they don't allow for the precise
technical definition of e.g. the required EQ. Apart from
that the probabily of making some simple but fatal error
is way too high for a reliable result.
Ciao,
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