I was looking for a used MiniDSP UMIK-1 measurement microphone and found the similarly priced Dayton Audio: http://www.daytonaudio.com/index.php/umm-6-usb-measurement-microphone.html . Then I came across this Omnitronic for half the price (around £55 delivered): https://www.steinigke.de/en/mpn13030923-omnitronic-mic-mm-2usb-usb-condenser-measurement-mic.html It's not calibrated like the other two but the frequency response looks pretty flat and is probably good enough fo