[SpHEAR-devel] latest musings (PCB, new Octathingy, calibration and more)

[Fernando Lopez-Lezcano]

On 06/23/2018 02:20 PM, Marc Lavallée wrote:
> Hi, and thanks for the news!

Hi Marc,

> I started a related project: building a binaural microphone, for
> measurements and recording, using very small Knowles capsules. One thing
> I have to learn is how to calibrate microphone capsules, and I found an
> interesting article about a calibration technique that doesn't require
> an anechoic environment, and I wondered if a similar technique could be
> used for the measurement and calibration of ambisonics microphones:
>
> https://www.scribd.com/document/321928725/Microphone-Calibration-by-Transfer-Function-Comparison-Method

They use SMART which is a (expensive) professional software to run a 
realtime transfer function measurement between the two microphones.

> Of course it'd be impossible to place a reference microphone at the
> center of an ambisonics microphone, but I guess it'd be fine to first
> measure the reference microphone (a few times for averaging) then the
> ambisonics microphone by making sure its center is at the same spot than
> the previously measured reference microphone. Does it make sense (or am
> I too optimistic)?

It does make sense and that is what I am doing (and presumably everybody 
else), but not in realtime as described in the article. I have a emm-6 
calibrated microphone that I use to have a reference measurement by 
placing it at the exact same position as the microphone being 
calibrated[*] - that measurement is used to create an inverse filter 
that "equalizes" the speaker, and that filter is then used to calibrate 
all measurements of the Ambisonics microphone...

After that the fun begins - making sense of the data :-)
-- Fernando

[*] well, not exactly the same position but as close as I can get it