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RME User Forum → FireWire & USB series → Rf interference and Adat
We had a strange problem on session this week - two of the Octamic channels were picking up a very loud radio signal, even after switching mics and cables.
Mics were connected via 40m of XLR/multicore and the Octamic was running at 96k into a UFX via SMUX.
Once I switched to the analogue outs of the Octamic the problem went away.
Any ideas?
ADAT does not carry any actual electrical connections so the Octamic may not have had a true signal ground with the UFX until you connected it via analog cables.
40m of mic cable is a long run, especially with dynamic mics. With my RCA44/77 ribbons I use a Cloudlifter head amp at the mic before the 100' snake. The Cloudlifter adds about 20dB.
Thanks Boz. So is it still a 'ground loop' when the mics pick up actual an radio station?
Yes. After connecting all the outputs ground was better so you could have used the digital output nonetheless.
Strictly speaking, I think 'ground loop' describes a situation where a circuit has undesirable currents flowing in the ground leads, often causing audio 'hum' or video 'humbars'.
This situation is more of an input that has an incomplete 'shield' connection, leading to RFI pickup. This often involves the additional feature of minor connector corrosion oxide acting as a diode to detect AM broadcast RFI that leaks in through the interrupted shield.
RME User Forum → FireWire & USB series → Rf interference and Adat
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