Yesterday I boom opped a commercial that had the strangest interference occurring over with wireless systems. It was a faint, fast, rhythmic rumble. It took the mixer and I all day to figure out the problem. Luckily the boom was clean, but it damn near drove us nuts trying to figure it out. We changed frequencies about a dozen times, which seemed to help in the short term, but right when we went for a take the sound persisted. We swapped it cables, and several other 'fixes'. Heck we even wondered if it was the boom acting as some kind of antenna because it would coincide when I raised my boom up for a take.
Turns out it was the camera's range finding system! They were using an ultrasonic range finder that was overloading the mic capsules of the Lavs. We would only hear it during the take because that's when the damn thing was pointed directly at the actors. Upon further testing we learned it was a purely acoustic problem with the small diaphragm mic being bombarded by the ultrasonic waves. The camera department said they had never heard of that issue before.
Has anyone else experienced this problem? I searched all around the web and all I could find was one forum on gearslutz. Here's the link for the curious.
https://www.gearslutz.com/board/remote-possibilities-acoustic-music-location-recording/911813-sound-killed-arri-udm-1-ultrasonic-measurement.html
Figured I'd posted about it so more info on the topic could be known.
Was shooting on the Arri mini. Attached to camera was the Arri UDM - 1 sonic range finder. We were using countrymen b3's and Sony UWP- D11 wireless.
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