[LAU] ABX test invite

[Ralf Mardorf]

On Fri, 2013-04-05 at 22:50 +0000, Fons Adriaensen wrote:
> On Fri, Apr 05, 2013 at 11:42:31PM +0200, Ralf Mardorf wrote:
> 
> > I made many tests not to get knowledge about my abilities, but when we
> > developed microphones, or even when we sold stereo pairs, several
> > employees listened. Btw. to find a stereo pair it's better to listen,
> > than to do measurements! Try to find a stereo pair of microphones that
> > fit together, by objective scientific measurements and ask people to
> > listen to microphones to find stereo pairs. I'll use the stereo pairs
> > from people who listened to the mics, not the pairs that were found by
> > objective measurements.
> 
> One of the more interesting jobs I've ever done was to define a procedure
> to select 4 matching microphone capsules for Ambisonic mics. That's a lot
> more difficult than finding good stereo pairs, and you can forget about
> doing it by listening. The only thing you could probably achieve that way
> is to identify a capsule as completely out of spec and unusable. 
> Nor can you do it by *simple* tests, which is maybe the only alternative
> to listening you can imagine. It requires, amongst a lot of other things,
> comparing directivity factors and phase response over the entire frequency
> range, using criteria that are matched to the question to be answered :
> can these four mics be used together for an AMB mic or not. It excludes
> factors that would easily lead you astray when listening but which are
> in the end irrelevant.

And you found a procedure to select 4 matching mics? IMO finding more
than 2 mics that match is nearly impossible. A stereo pair for sure must
not be that perfect. I believe that you find a procedure to select mics
by measurements, but I have doubts that there is a capsule vendor that
is that good, that you can find 4 double sided large-membrane capsules
that match. If you limit the characteristics, IOW if only one side is
important, or you use electret condensors and in addition without tubes,
this might be possible, but IMO selecting double-sided large-membrane
tube microphones can be done best by listening and only for stereo
pairs. Resp. you can find 20 mics that match, it's just a question of
time and money ;).

For private home recording IMO it's possible to get relatively good
results with elCheapo mics that don't match. But that's home recording,
nothing you can sell.

I'm thinking about microphony because any thing in a sound chain, e.g. a
codec, could cause panorama issues. If there's a little bit loss, it
could be that the sounds of the instruments still do sound equal, but
when you listen by headphones the lossless mix might surround you, while
loss that is inaudible for the instruments, could cause that the sound
of the recorded room doesn't surround you anymore, but seems to come
e.g. more from the front above. I'm not talking about 2D or 3D, but
profan stereo recordings, that involuntary become 2D or 3D by loss.

FWIW I'm only experienced with stereo, not with 2D or 3D and I guess
most engineers are inexperienced with 2D and 3D, however, assumed MP3
can be used for stereo, it would be interesting to know, if MP3 or
another codec with inaudible loss, is able to keep the mix for a real 2D
or 3D recording. I don't know how data reduction does work, but I guess
there's an effect similar to a compressor (the effect app or device).
You can link the compression for the left and right channel and you can
compress the left and right channel individually.