Wireless mic static

Discussion in 'Microphones (live or studio)' started by magic2sound, May 19, 2018.

  1. magic2sound

    magic2sound Active Member

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    Location:
    Florida, USA
    I have a Sennheiser transmitter-receiver ew100 G3.

    It's going into a Canon XA20 pro camcorder, into the Input on the Handle, which is set to Mic/Manual/flat (center). It's always worked fine for me until lately.

    I moved into an apt/hotel where the only Internet is their WiFi. I started noticing static/hissing in my videos, and to troubleshoot it I moved all wireless devices to another room, and even turned off my watch (Bluetooth). I did leave the computer on, which sits right behind me, and left the USB WiFi adapter in it, but that's all I left on and it's nowhere near the path between the mic transmitter and receiver. The receiver is 9 feet from me. The transmitter is 3 feet from the computer and WiFi USB adapter.

    I even changed to a different set of the ew100 transmitter and receiver, which I had on-hand, and that didn't fix the problem.

    The problem is intermittent. I recorded a 12-minute video today and the audio was perfect through all of it except the short segment in this video:

    https://vimeo.com/user37098169/review/270923144/96f168555a

    I need to find a solution. I'm hoping setting the ew100 to a different frequency or something?

    (I guess it could be that WiFi USB adapter in the front of the computer sitting under my desk, but I need that and I would love to find a more cut-and-dried solution -- and I just "suspect" that that won't resolve it.)

    Thanks!
     
  2. dvdhawk

    dvdhawk Well-Known Member

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    Hello and welcome.

    Changing the frequencies on the Sennheisers would be the first line of defense.

    What frequency band are they operating in?

    Do either you, or the subject, have cell phones in your pockets during this time?
    It’s not enough to silence the ringer, they may have to be powered off. Airplane mode may suffice, but OFF is better.

    Have you observed a regular time interval between static bursts?
    Record an hour or two of nothing and see if there’s a pattern.

    It’s a place to start.
     
  3. paulears

    paulears Well-Known Member

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    That's NOT static, as in interference, just low RF. Nothing to do with external noise sources. There are always dead spots you cannot predict, and of course there are some real faults that reduce the signal output - usually antenna dry joints just inside the transmitter, where pressure from tight fitting causes it. You also have unpredictable signal paths, and sometimes reflections that create dead zones. First question - where was the pack on his body? Where was the receiver? Even a short path that has to go through somebodies sweaty body can create this noise. I do loads of stage work, and this kind of thing is so common, and often affects just a few people. Stick a mic on them, and allow the antenna to touch their body and the RF drops drastically - even more annoying when somebody else seems to work anywhere! What can you do? Receiver location is paramount. I assume you are using the battery powered receiver rather than a rack type? Put the receiver on the top of the camera, as high as it can go without anything between it and the transmitter. On the person if his waist is not in shot, attach the pack to the side or front where it's antenna is clear, and nothing between. Double check under controlled conditions the range you get without the signal dropping down and producing the phutt sound. In the clear, you should get a fair distance, but metal is bad - sometimes, the closeness of metal, perhaps the chassis of those screens, works as a reflector for the RF and it creates nulls - areas where signals just cancel. Usually move a foot or two any direction and it comes back, but it's easy to find these dead zones. All that happens is the RF signal drops below the threshold and despite a short path - it's a rotten one. This is why diversity radio systems are so useful - the path from source to antenna 1 may go down, but the receiver can switch to path 2, to the other antenna. Even the more expensive receivers suffer a bit because their two antennas are just too close together. We get really fed up when all goes well in rehearsal, then they all start to sweat and the bodies on stage act like RF absorbers, soaking up the signals as they god from source to destination.
     
  4. magic2sound

    magic2sound Active Member

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    Wow! That is remarkably informative. Thank you! And it's quite consistent with my experience. (By the way, I'm the "talent" in these situations -- it's just me shooting business videos for my nonprofit and my manufacturing company, working alone.)

    The reason what you described is consistent with my experience is that one thing I've noticed as a pattern when observing playback of spots with that sound issue is that it seems consistent that my arm was moving when it happened, probably every time.

    The receiver is the battery-powered type. It's on a tripod next to the camera with nothing at all obstructing the path. Its antenna is about six inches away from the edge of the 7-inch monitor I mounted on top of the camera (good pro brand of monitor). The antenna might be touching the cable that comes out of the top of the receiver, but I'm guessing that's not likely to be an issue. (I'm guessing the design wouldn't have them next to each other and touching by nature if that was an issue. The cable is "behind' the antenna, so it's not impeding the path.)

    On the other hand, the transmitter has bee on my belt on my side while I sit in a chair. I would surmise that my arm has been touching. As I move my arm to make hand gestures while I talk, I'm sure it's been rubbing against the antenna and has been intermittently blocking the direct path.

    Since these videos are all strictly dealing with "head-shot" framing that doesn't go below the middle of my upper body, and my waist is out of the frame, I do have the option of keeping the transmitter off my body and on a tripod that's in front of me so I'm not touching it or blocking it with my arm. The length of the lavalier mic cord is more than sufficient to give me plenty to work with.

    Does the height of the transmitter matter relative to the height of the receiver? Keeping the transmitter elevated will be more of a challenge. Right now, the transmitter, to be "below" the frame, will be about 24 inches off the ground, while the receiver, which is about 8-10 feet away, is about 5 feet off the ground.

    Thanks so much!
     
  5. paulears

    paulears Well-Known Member

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    The distances involved are quite short - so these signal strength reductions do seem severe. I would do the test as soon as you have some time. Go somewhere empty - a field is ideal - set up the receiver into the camera, and then with the mic pack held in front of you towards the camera, start to speak in 'paces', and walk away from the camera. In open space, you should be able to get at least 40 paces away without 'phutts' . If you don't then there is a proper fault. Probably in the antenna connection of one of the units. Once you establish the useful distance (with an assistant?) you can then go a little further till signal cuts out, then get the assistant to wiggle their end, and you do the same the other. If it's a dry joint or similar, the distance may suddenly increase. If you get 30m plus - call this normal. low signal less than this indicates barriers. Bodies are actually very good absorbers of RF energy - being mostly water! IF you have a body soaking up 180 degrees worth of the output, and then reflections range can drop very quickly.

    If you do these kinds of shoot often, I'd use a wired mic every time. I have plenty of RF systems - Sennheiser mainly, but I use wired mics whenever the cable isn't a problem. The worlds best RF radio system is nearly as good as a £10 cable.
     
  6. magic2sound

    magic2sound Active Member

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    Thank you again. What's perplexing in the context of the test you describe is that I've used this setup elsewhere before with no issues ever, and in fact, as mentioned in the OP, to troubleshoot this I switched to a different transmitter-and-receiver set but the problem was unchanged! (Even the cable from the receiver to the camera handle is changed.)

    Doing the test you described is also a challenge in that it's an entirely intermittent issue. Even after it began occurring, I've shot "dozens of minutes" of video in multiple shoots with this current setup without any of that RF noise at all. And then it occurs.

    So, I have to assume the arm in front of the antenna and touching the antenna is the issue. It's consistent with what you described and consistent with what I'm observing on playback. I'll play with that and hope for the best.

    Which again brings me to the question, please, of whether the height of the transmitter matters in this setup.

    Thanks again!
     
  7. magic2sound

    magic2sound Active Member

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    The height is a question even more so in light of the fact that, in thinking through what might be different here from what I previously had set up for years in a studio without ever having this issue even though the transmitter had always been on my hip like it is now, is that now my chair and the camera are at least a foot lower if not more (in the studio, I used to sit on a stool and use a foot-stool for foot pedals to control a teleprompter). So, the transmitter now is perhaps 1 to 2 feet lower relative to the receiver compared to how it used to be.

    I do currently have the option of lowering the receiver about 18 inches, and raising the transmitter a bit, in order to bring them closer in terms of the horizontal plane.

    Hence, my question about whether heights are likely to matter here.
     
  8. paulears

    paulears Well-Known Member

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    Two more things you could check - orientation. of the antennas - they MUST match. If they are at 90 degrees to each other - so one horizontal and the other vertical, or both at 45 degrees, but each the wrong way from vertical, almost complete cancellation can occur. Earlier we were all concerned about interference, and I poo-poo'd this. I probably should explain this a bit better. Mobile phones are notorious for interfering with that nasty buzz-saw stuttering sound, but that is being picked up by the audio circuitry, and isn't an RF issue. If your receiver is set for example, to 607.5MHz, then strong radio systems in the VHF band, and walkie-talkie type radios in the UHF band are far enough away that they shouldn't cause grief. However, a strong RF signal very close - say on 608.5MHz will desensitise the receiver, making it, in effect, deaf - so even small drops in RF produce this weak signal effect. It's quite rare for signals this close to cause desense - because the usual problem is intermodulation interference - and you hear this as strange warbling and odd whistles and whines. You've probably concluded there are no other radio mics operating close to you, so while you could have something local that is very strong, it's a bit rare. In the UK, ch 38 is surrounded by two unused channels - so our closest one that is powerful and active is around 620MHZ - (ch 40) - and it's just possible that if you are very close to this, desense might occur - but very unlikely. I can't comment for Florida. Desense gets quickly less problematic once you get 6 or 7MHz away, and by 15MHz, virtually trouble free.
     
  9. magic2sound

    magic2sound Active Member

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    What about heights?
     
  10. paulears

    paulears Well-Known Member

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    Height is only a factor in avoiding obstacles - one low and one high or vice versa makes no difference in free space. Both high or both low the same close in. Once we start introducing losses, then height can move the antenna into safe space. We have racks of receivers, and there is antenna distribution inside the box - so with 6 -12 receivers in the rack, each with two antenna sockets - we have just two connections for antennas - these could have small rubber duck style antennas fitted, or remote paddle type antennas on longer cables. From the rack to a microphone within 10m or so, the links is usually ok, but for added security, we'd usually separate the antennas and use directional paddles - this usually ensures that even if somebody stands in a null for one antenna, the other one is in the clear.

    In practice, having a receive antenna above head height provides the best route to the transmitters. With antennas lower down - people and things can easily get in the way and wreck a perfectly good link. It happened quite a few times in the Royal Wedding coverage. A perfect route on rehearsal, then it gets blocked when thousands of people turn up. Life's a bugger sometimes!
     
  11. magic2sound

    magic2sound Active Member

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    Got it.

    So, in my case, it seems I may as well bring the heights a bit closer in line since I can, but I should hope (and expect?) that keeping the transmitter on a tripod in front of my body rather than on my hip will be the difference that makes the difference.

    Thanks so much!
     
  12. paulears

    paulears Well-Known Member

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    Personally, I'd not bother with a tripod for the transmitter - I'd just make sure the receiver can physically see the pack. if the two antennas are in the same plane, with nothing between them - that's as good as you can get.
     
  13. magic2sound

    magic2sound Active Member

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    I was thinking my arm touching and/or blocking the antenna on my hip was the culprit. Where else would I put it, then, to avoid that possibility?
     
  14. paulears

    paulears Well-Known Member

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    Well - it would but with the antennas in direct line - the occasional had wouldn't cause problems - you can lose lots of signal before they react badly. Remember that radio works with the Inverse Square Law. If you double the distance, you drop the signal to a quarter of what it was, and if you half the distance, it doesn't double - it quadruples. Your problem was almost certainly a number of things that contributed. If I was ten feet from the camera, I would expect my systems to behave. Do the distance test to make sure the power output is holding up and antennas functioning properly then report back.
     
  15. magic2sound

    magic2sound Active Member

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    Well, going back to what you said in your first post, and given there's little else that makes sense, I have to assume the hand/arm has been a factor. What doesn't make sense to me, though, is why that wasn't an issue in the studio. So, I'm pretty stumped.

    I don't really have a lot of variables to adjust at this point other than that, and it's easy enough to try. After years of computer troubleshooting, well, that's my next attempt. It's logical, the process of elimination leaves little else, and it's the easiest thing to change. I just wish I could explain why it was never an issue with the studio I was in before.

    Oh, wow. One thing I did just notice is that the antennas are each bent back at an angle, and with the orientation I've been working with that resulted in their being pretty much at 90 degrees to each other -- perpendicular. So, that's another variable for me.
     
  16. magic2sound

    magic2sound Active Member

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    >> Oh, wow. One thing I did just notice is that the antennas are each bent back at an angle, and with the orientation I've been working with that resulted in their being pretty much at 90 degrees to each other -- perpendicular. So, that's another variable for me. <<

    Maybe reflections in the studio made up the difference, which don't exist now.

    At least now I have a couple things to adjust and hope to get results from.
     
  17. dvdhawk

    dvdhawk Well-Known Member

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    I have the Sennheiser ENG systems and they are quite reliable over 100 feet - all other things being equal. But to Paul's point, if I were shooting a headshot less that 25 ft. from the camera, I'd use a wired mic if at all possible.
     
  18. paulears

    paulears Well-Known Member

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    If you experiment a bit, with headphones on, but without the mic plugged in, you can see how distance, objects and antenna polarisation impact pin your kit. We've given you the essentials, and now you need to do some tests. RF works in mysterious ways, rarely behaves the same twice, and distances can vary so much from day to day from location to location. No sensible person risks radios if a cable is available. Many famous names who use radio systems - like the comedians insist on a cable mic being available as a backup. When the radio dies, the cable always solves the issue. The usual trouble is that the radios systems nowadays are so good at not showing problems, until the problem becomes just too much, then all hell suddenly erupts. Digital systems are even worse - they just stop with no warming at all. - Analogue allows a skilled operator to hear problems before the audience does, noticing the little artefacts creeping in. Some of the worse offenders are radio systems where the receiver clips to the top of the camera handle - and the antenna points towards the talent. The absolute worst case scenario you can have. I'd love to say all the things we're talking about will cure it, but they won't. They just reduce the problem. Will your issue happen again? Yep. Almost guaranteed.
     
  19. dvdhawk

    dvdhawk Well-Known Member

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    In a moment of clarity this morning one other thing occurred to me. This could also be as easy as adjusting the pilot/squelch settings on the Sennheiser to gate out more background RF.
     
  20. magic2sound

    magic2sound Active Member

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    I'll try repositioning the transmitter and adjusting the pilot/squelch.

    What's most perplexing to me is the fact that the same issue has manifested the same way with two separate pairs of the transmitter-receiver. Very odd indeed. Maybe it does in fact point towards "background RF" that pilot/squelch might resolve. (I have no idea where it might be coming from since nothing is within dozens of feet. I might also point out that I'm a novice here and know nothing about background RF or pilot/squelch, but I'll look it up.)

    Thanks again!
     

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