Topic: what the heck is this sound?

[nulldogmas]

https://soundcloud.com/nulldogmas/interference/

There's a clunk toward the beginning of this sample, so it's possible this was the moment when my M10 almost slid off my lap, then I hurriedly caught it after it fell maybe three inches. I still don't get how this would cause the interference that followed, however. (Which didn't recur during the rest of the show.)

Mics were AT-853 cards, into a UBB, into the M10. Was also running CSBs into a SP-SPSB-1 into another M10 on the same stand, which didn't pick up any interference.

[danny3]

link gives me a "we can't find that track" message

[nulldogmas]

link gives me a "we can't find that track" message

Try again now?

[voltronic]

Cell phone noise.  Even with balanced cable runs (which you didn't have), it can get into your recorder directly.  Airplane mode is your friend!

[nulldogmas]

Cell phone noise.  Even with balanced cable runs (which you didn't have), it can get into your recorder directly.  Airplane mode is your friend!

Even if my phone didn't receive a call then? And if so, how come this was only picked up by one of the two recorders? Different length cable runs?

Also, my phone is a Verizon iPhone, which by my understanding is CDMA, so shouldn't be causing interference like this.

[flipp]

It didn't have to be your phone causing the interference. Unless you had at least a 5' radius with no one else around you it very well could have been a phone you never saw.

[Fried Chicken Boy]

Definitely sounds like cell phone interference.  Doesn't matter if you received a call or not, it could be from a text, pushing emails, the phone updating something or checking in with the network, etc.  Or, as flipp noted, it could've been your neighbor's phone.  Since it was just present on one of your recordings, different cable runs or shielding in one of the components is the likely culprit. 

[Bruce Watson]

Even if my phone didn't receive a call then?

Surely you know that your cellphone (and everyone elses) is constantly pinging the local tower(s) so that the cell phone system can find your phone if it's called, and so that your phone knows which tower to talk to should you decide to use your phone for something. So yeah, even if you didn't receive a call right at that moment, your phone could have been talking to the tower(s).

And as others have said, it doesn't have to be your phone. Some phones leak more RFI than others. And then there's pagers and other devices. Not to mention actual radio mics and radio monitors (a lot of IEMs are run from the FOH mixer via radios so the band members can roam about as they play).

And it doesn't have to get into your system via mic cables. One of the easier paths is through power cables; battery operation cures that one. But I've heard of more than one case of RFI getting through the mic itself. When it's that bad... you're just sorta screwed.

[nulldogmas]

I was running on batteries, so power cabling wouldn't have been it. The AT853s have somewhat longer cables than the CSBs, so maybe that made them more susceptible? (This is the first RFI problem I've had in a recording in 14 years, FYI, and also these AT853s are fairly new to me.)

If somebody adjacent to me had a phone throwing lots of RFI, I would think it would have been a problem at more than just that one moment. But I guess it's not worth worrying over at this point — it sounds fine enough with a patch from the other mics.

 

[voltronic]

Bruce pretty much summed it up - there are a number of ways that a phone can be active when you think it is idle, and a number of paths that interference can sneak into your signal chain.  And you never know when it's going to happen, unfortunately.  The only way to eliminate it is to have you and also everyone else near your equipment put their phones into airplane mode or power them down.  Good luck with that!

Case in point: I have a set of powered KRK monitors at my desk connected by balanced cables to my Focusrite Saffire external FireWire interface.  The fact that I'm using FireWire, with a dedicated FW card (much more crap going on in your computer on USB), to a fully metal-enclosed interface box, with balanced cables to shielded monitors would make you think that I never get cell phone noises.  Not the case.  Sometimes when I have my phone on the desk next to my keyboard, there is the telltale noise in my right monitor as my phone is doing whatever it does on the network.

Even well-made balanced cables can sometimes let in RFI, sometimes the connectors are at fault.  Neutrik makes the EMC series XLR connectors specifically for this reason.

Again, your 853s have a long unbalanced cable run, with another (very short) unbalanced run from the UBB to the M10.  So it's not at all surprising this happened, even though it may seem very random.  I think you've been very lucky that this is your first RFI incident.  I'm not suggesting that you have to go out and buy new things; just that it's one of those things that happen.  All you can do is minimize the chances, but like my example above, it still may creep in.

[rhinowing]

I think you've been very lucky that this is your first RFI incident.  I'm not suggesting that you have to go out and buy new things; just that it's one of those things that happen.  All you can do is minimize the chances, but like my example above, it still may creep in.

agreed, I get RFI issues on usually 2-3 tapes per year, minumum

[nulldogmas]

Again, your 853s have a long unbalanced cable run, with another (very short) unbalanced run from the UBB to the M10.  So it's not at all surprising this happened, even though it may seem very random.  I think you've been very lucky that this is your first RFI incident.  I'm not suggesting that you have to go out and buy new things; just that it's one of those things that happen.  All you can do is minimize the chances, but like my example above, it still may creep in.

The one thing it may encourage me to do is to keep running a pair of redundant recordings whenever possible. Having the CSB source (which I'd only set up for comparison purposes) to patch in reduced this to a minor annoyance; if I had to live with that interference on the final product, I'd be pretty miserable.