Reading through this thread I feel the other responses may not have
given you a clear picture. There are lots of very capable Ambisonic
practitioners on this list, but sometimes they forget that beginners may
not understand the formal terminology (or the in-list banter).
The simple answer is that you cannot manipulate a set of A-format
signals and then convert them into B-format. A-format is simply a set of
microphone signals with very precisely-known characteristics and from
precisely-known directions (LFU, RFD, RBD, LBU - note the U (up) and D
(down) components; it's not simply LF, RF, RB, LB). Normally the only
possible manipulation of the A-format signals is correction for
calibration differences between the microphones and compensation for the
distance between the capsules if you are using a soundfield-type
microphone; this manipulation is done to the A-format signals to improve
the A-format to B-format conversion.
The Ambisonic signal as such exists as the B-format data. In this form
only it can be rotated, focussed, made to behave like sets of virtual
microphones of different character, etc. Nowadays this is much more
easily done in the digital domain rather than by analogue mixing. But
the A-format signals are not an analog of quadrophonic signals; if you
mix/rotate the A-format signals before converting them into B-format
what you will end up with is a set of signals that _cannot ever_ be
converted into Ambisonic B-format. To attempt to do so just doesn't make
any sense.
OK, I've simplified things a little in this explanation; the more
scientific- or mathematically-minded list members will probably burn me
in effigy for heresy. ;-) But I think you needed a simpler, more direct
explanation than you had got before now.
Gerard Lardner
On 26/09/2013 23:22, Kan Kaban wrote:
Sorry Mr. McGriffy & Aero for the wrong quote, I don´t do lists since some
years ago.
Thanks a lot for all this info to everyone, I really appreciate your concern.
Now I have a lot to do...
I´m sorry if some ambisonics terminology is not being used as intended. I hope
you understand.
The idea of using a quadraphonic panner (previous to AB conversion, came from
Mr. Gerzon´s paper:
"A-format consists of four channels LB, LF, RF, RB compatible with existing
'discrete' practice for the four corner positions".
Please correct me again, but I read that A-format is Lb / Lf /Rf / Rb. So seems
logical & possible to me (sorry I that´s offending anyone) to use a
quadraphonic panner before the AB converter.
I suppose that´s not a full ambisonics panner, but at last will do the job as a
starting point. Isn´t it?.
Soundfield´s MKV looks beautiful & very interesting too.
Regards,
Gino.
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