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Wireless mic static

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

  1. paulears

    paulears Well-Known Member

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    Feb 7, 2014
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    Lowestoft - UK
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    Not really - all that does is makes it go dead earlier - squelch set near the threshold reveals the noise floor rushing up and the little pops and clicks. Turn up the squelch and as soon as the signal falls to the danger zone, you don't hear them - but neither do you her the wanted audio. You get the choice of noisy audio or no audio - neither very useful
     
  2. magic2sound

    magic2sound Active Member

    Joined:
    May 19, 2018
    Location:
    Florida, USA
    I'll play with positioning first. I'm optimistic that will make the difference. (It will be a few days before I'm ready to do more shooting and only then can I really test it since it's so intermittent I have to just shoot real footage and then check it afterward.)
     
  3. paulears

    paulears Well-Known Member

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    With respect - that's a bit daft (or skew-wif as my mum used to say). The thing with radio mics is that to do it properly the operator (sound or camera) listens all the time and they can hear the onset of the problem before the audience will. If you just wing it each time, surprise comes at the end of the take - assuming you have time to check each one, so learning how your system works best is surely worth spending a few hours experimenting with? Doing some tests, establishing if you can make them misbehave and therefore getting a grip on circumstances where you could accidentally spoil the path. Hearing the onset of noise as you rotate a pack, and seeing the kinds of angles where it disappears is a skill to be learned BEFORE it's critical. If you were going to become a surgeon, would you wait till the next operation to see if your new ideas worked? That's just backwards thinking. You are being reactive, rather than proactive. So many people just assume RF systems are solid and reliable and whenever you have a day with no glitches, this was the lucky day, not the norm. In my theatre shows - I employ a person to monitor radio mics - they fit them, they adjust them, they continually monitor the RF levels, they listen to them and can prevent many problems - enough to justify their pay. In this world of tight budgets, I'd never have them at the top of my list for cost savings. It's a rare day when I don't have to include something in my daily reports about radio mics. A totally clean show is a rare thing. Have you noticed how many critical radio mic jobs are done with TWO mics and two packs?

    Please find some time and experiment before your next job - or this entire topic has been pointless.
     
  4. magic2sound

    magic2sound Active Member

    Joined:
    May 19, 2018
    Location:
    Florida, USA
    That's very good advice. I really didn't even consider that. Playing with tolerances -- and noticing patterns and thresholds if I'm able to -- would be really useful indeed. Makes perfect sense. Thanks again!
     
  5. dvdhawk

    dvdhawk Well-Known Member

    Joined:
    Dec 18, 2008
    Location:
    Western Pennsylvania, USA
    I do not share Paul's cynicism regarding squelch settings being all or nothing. And I believe the engineers at Sennheiser are perfectly capable of designing squelch circuitry that does exactly what squelch circuitry is supposed to do in this case. Certainly, if set too high it gates out the good with the bad, and if set too low it lets backround radio noise creep in along side your signal. I'm not saying adjusting the squelch is the solution, but it is another thing that you might want to experiment with while you're scratching your head looking for answers.

    The pilot tone is a simultaneous frequency transmitted from the Sennheiser transmitter pack. and when the "Pilot" setting is enabled on the receiver it will mute all RF unless that pilot tone is present. And again, key-tone, or pilot-tone squelch (depending on the manufacturer's terminology) is not always the answer for the myriad things that can cause drop-outs or interference with wireless mic systems.

    To Paul's overarching point, wireless mics are 50% voodoo. The time to experiment is before you're shooting something that matters.

    Other than via the camera, do you have the ability to monitor the output of the receiver pack? Experiment in your new environment monitoring the audio components outside the camera. If necessary record a couple hours of nothing on the camera. If you use an NLE (Premeire, Vegas, FinalCut) drop the recordings into the editor. The unwanted noises should be pretty apparent amid the relative silence. If you change positions of things during the test recordings, state what you're doing on-camera so you have a record of what things had an effect on the noise situation.

    Carry on.
     
  6. magic2sound

    magic2sound Active Member

    Joined:
    May 19, 2018
    Location:
    Florida, USA
    Testing is a challenge for me due to time and resource constraints. But I will do my best.

    Meanwhile, I want to ask for help with a specific angle if I may, please.

    In the context of my experience with troubleshooting computer issues, the following logical observations seem to be potentially very relevant to me and might help experienced audio experts deduce what is and is not likely to be the issue here (I know I've stated the following already but I'm thinking it might be pretty revealing and help narrow things down):

    1. I have used the same camera and same transmitter-receiver set(s) for years in a different location but under virtually identical conditions in terms of the orientation of the equipment, the sole difference being that now the transmitter is not as high. In all those years, this issue never occurred one single time. But in this new location, it's happened frequently, on about 50% of the videos I've recorded, averaging about 8 minutes in length.

    2. This same issue is manifesting in this new location about equally with two different sets of transmitter-receiver pairs.

    That, to me, seems to essentially eliminate the chance that it's either the equipment or the orientation of the equipment -- unless the two-foot difference in the height of the transmitter could be the culprit in and of itself.

    Well, I"m using a different camera, too, but it's the identical make and model as I used those few years, purchased at the same time, with I believe all the settings set identically. And I think we can agree from the sample I provided it is not in the camera.

    It seems that would leave external RF interference as the only likely culprit -- assuming external RF interference can come from quite a distance. (Or can come from the computer, and/or the powered computer speakers on the desk, and/or the USB WiFi adapter plugged in the computer. Or else, what? The USB charger block sitting on the desk a foot behind the transmitter? I'm a novice but from what you've been saying in this thread, I believe you've said that none of my computer equipment can be causing this since this is an RF issue.)

    I'm living in an extended-stay hotel and the next nearest room is a good fifteen feet away, meaning the nearest possible location for an RF to be coming from is...

    Oh, wait a second. They use walkie-talkies here! The management carries them all over the property. I'm guessing you're going to tell me those use RF and that that transmitter/receiver scenario is potentially enough to interfere with my wireless mic system.

    So, let me just ask:

    1. What's the odds that their walkie-talkie equipment is the culprit?

    2. If it's likely that it is, what would then be the most logical solution?

    Thanks again!
     
  7. paulears

    paulears Well-Known Member

    Joined:
    Feb 7, 2014
    Location:
    Lowestoft - UK
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    Inverse square law applies - double the distance and the signal drops to a quarter - so for external RF to cause desensitisation rather than interference, it has to be close, or powerful - and both would be very bad. RF wireless has very characteristic types of artefacts - You can get nasty spikes that produce transient interference - loud click or bangs, but these are quite rare. The strange phasey/wobbly/phantom voice style noise - weird noises in the background that seems to morph and change - these tend to be intermodulation - where the problem is transmissions on a different frequency, but one where two or more signals combine in a non-linear manner. This depends on both the receiver and transmitter specs, and is why people like Sennheiser put together frequency lists for multi-channel operation that work on specific models. Using a list from one model on a different on works VERY unpredictably. It's also why you can often get away with two randomly picked frequencies, but the presence of a third makes the world go mad! Very often the third pack moving closer and the second one moving further away suddenly destabilises everything.

    All things being equal - if we are talking about ranges of a few feet, the signal strength should be strong enough that any antenna orientation should still capture sufficient signal. If two receivers behave differently, then one is faulty - if both suffer the same problem on the same frequency (and especially different frequencies) then the usual cause is reflections creating nulls - think of these as RF black holes. You can squirt 50mW from these locations and the antenna you can see on the receiver gets zilch. In pretty well every case, moving the transmitter or receiver antenna will work wonders. We still have some original series Sennheiser, and quite a few IEM systems, and a frequent complaint is where the user stands quite close to the other end, and it goes weak and noisy. Move further away and signal strength goes up. Contra-common sense, but reflections do cause this kind of issue.

    At one venue the bass player complained that he was getting lots of noise - the transmitter to his IEMs was in the rack with his other equipment - a 12U rack with amps, stage boxes, 4x IEMs and other random kit - the antennas were vertical-ish on the rear, and the rack itself was a real obstacle to the RF. However, after noting the IEM frequency so we could avoid them - we discovered his IEM feed was loud and solid at the back of the auditorium - 40m away!


    It is possible that you have a local very high noise floor in the radio mic band, but I've never come across this in any case where it was not accompanied by nasty hums - a wide band noise source would reduce range - but in analogue systems, this behaves like co-channel interference which you would hear? Two carriers on the same channel type noises. With capture effect, FM receivers tend to hone in one one or the other, kind off keeping it, till the other is stronger, then switching allegiance.

    You really have to find some time, don't you? You've had loads of suggestions and tips - now you have to do something, or put up with it really? Testing will hopefully point you to the culprit, and provide some handy background knowledge.

    As you have two systems, you can easily explore how your system reacts to co-channel interference, and desense - by shifting the frequency away a little then bringing it closer, and hearing what happens - then maybe you will know better what exactly your issue is.

    As for squelch - operator preference decides on how tight you run squelch. Do you want usable but noisy audio, or only good solid audio? Is constant cutting out and in better than fizzes and photos? Personally - you can with practice, nurse a noisy signal riding the fader - an intermittent signal is obvious to everyone.
     
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