On 04/23/2018 03:19 PM, Fons Adriaensen wrote:
On Mon, Apr 23, 2018 at 01:10:56PM -0700, Fernando Lopez-Lezcano wrote:
In my case to get good calibration data I need to rotate the microphone with
no wobble and at different orientations (or if it is not _exactly_ perfect,
try to get away with calibrating out the average delays to all capsules).
There's practically no way to obtain precise positioning,
Yes, I get (measurable) wobble even after "calibrating" the position of
the array (I have a small XY table at the bottom of the rig to be able
to offset the center of the array with respect to the center of
rotation). No way to make this "perfect", just the stiffness of all
parts and play is enough to create small errors.
unless you'd use a robot to rotate the microphone,
Funny you would say that, I have a robotic arm on order (I should have
gotten it a couple of weeks ago but some part was apparently on
back-order)...
and that comes with its own sort
of potential problems (like reflections on the robot arm).
Indeed, at this point I'm not sure it is going to be a solution, or just
another problem :-) A robot arm that is big enough to be "out of the
way" would be way too expensive. Very cheap ones are too small and don't
have enough carrying capacity and precision. Some are obviously too
"fat" and will be a pain in terms of reflections, or too short and not
enough reach. We'll see if what I'm getting is good enough...
At least it should make the task of doing many repeatable measurements
not so insane, at this point everything is manual (I am the robot).
Of course driving the robotic arm so that it positions the center of the
microphone at the right spot is probably not going to be easy either.
Again, physical interface, tolerances, play... Hmmm, jack-delay and arm,
feedback loop, hmmm[*]...
The only practical solution is to make the processing software detect
small position (and other) errors and compensate for them.
I reached the same conclusion, and that is what I'm doing now. So far it
looks like an improvement.
-- Fernando
[*] unstable system, the arm goes wild and destroys the microphone,
nothing left to measure!, bliss.....
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