From what I read in the past, the latency of USB microphones tends to be rather unpredictable. I have no personal experience with such microphones, though.
I can't speak for anyone else, but despite a change in priorities, my two expressed goals have not changed from day one:
I would think that would also be the case here. I have had friends find that single channel USB interfaces don't work for recording looping music, I would imagine that the effect would be worse when trying to use for measurements (in this context).
It is an explicit requirment for the measurements to be accurately time referenced. The best way to do this is with a dual channel measurement from an analogue microphone. With a good or even average interface ASIO or WDM driver there is no problem capturing this with Windows or any other operating system.
USB mics bring a lot of timimg problems to the table. There are ways around it but I would recommend for the sanity of anyone trying to do this that they leave the USB mic in the drawer.
Thanks, I will discuss it with NTK to see if he is still interested and what was missing from the previous information.
I still think Sound Field separation for the 200Hz to 1K region is a worthwhile addition if it can be done without the need for a full blown robot.
Perhaps with some optimization of acoustic centre and symmetry the number of points needed might be small enough that manual or semi automated become worth looking at, that was my hope.
Can you explain how this is an addition compared to gated measurements?
With a bit of space 200Hz is absolutely no problem at all with gated measurements.
Any issues or resonances problems at these lower frequencies can be seen with near-field measurements.
I don't think there is any value in that. The code has been tested with simulated data already. The next step is actual real data from known points, even if that is limited number of points.
The resolution with a gated measurement that has a 200Hz validity starts to get progressively worse below 1K. There is only 5 valid points between the two frequencies. This results in a lot of smoothing. If you want an accurate measurement of the directivity this is not enough.
As you say there are ways to check that nothing untoward is hiding in that smoothing. A valid and practical approach.
I want to be able to measure the response and directivity of a speaker accurately across as much of the frequency range as I can, hopefully without spending US 100K or building a full blown robot, or lifting the speaker 10m in the air
That totally depends on the answer to the question how much is even needed?
If you can already predict beforehand that there will be zero issues and problems below 500Hz, why do I need so much more accuracy?
Indeed, I think something near a 15ms window would be enough resolution for me. The equivalent of 1/3 octave smoothing at 200Hz.
I am not saying that you do. If you are happy with what you have now that's great. Why is it a problem for me to want to do better?
Nice explanation. I have 14 mics. I used to think that I can do this either USB or analog. Analog is the way to go. I'm convinced enough. Got me thinking! Thanks.
Honestly, I don't think that it can. As far as I can tell, sound field separation requires a full 3D measurement. This adds a huge complexity and expense for a small gain IMHO. Nice to have sure, but it'd also be nice to have the 100k+ $ to just buy a Klippel machine.
What's the purpose of getting as high of a resolution as you can get if it's not needed?
Not only that, but why wasting time and effort to something that has zero or very little benefits?
Just getting more information for the hell of it makes zero sense to me.