Looking for a good lavalier mic that is impervious to GSM / cell phone interference
 

I have some Audio Technica AT803B microphones that do a great job, but they are very susceptible to the "GSM buzz" or cell phone noise. (If you're not familiar with the noise, check out http://www.dvinfo.net/forum/all-thin...nal-noise.html)

Anyway, I'm looking for a similar mic that would NOT pick up the noise. I think this must be possible because I have shotgun mics that don't pick it up, and I also have wireless sets that don't pick it up. So I would assume there's a similar mic that doesn't pick up the noise.

Any thoughts?

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

At what distance? Using what other equipment?

If you are looking for something that is impervious to a cell phone in another pocket of the user (the wearer of the lav mic) then you are dreaming. The RF field is so great at short distances that NOTHING is really "impervious". Certainly not baseband audio equipment, and especially not high-impedance, very low-level devices like electret microphones. The ONLY cure for this situation is to turn off or remove the phone from the user.

Note further that SOME of the vulnerability is in the wiring and/or connectors, and particularly in the input circuit of the terminating equipment (i.e. the wireless transmitter or the XLR adapter, etc.) You can do some limited "RF hardening" to some equipment.

But there is almost nothing worse than a pulse-mode GSM cell phone, especially one searching for a cell connection. They put out a stream of RF pulses that resembles the kind of jamming that was commonplace during the cold war in the repressive communist totalitarian regimes of eastern Europe.

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

The most common scenario is in a conference room, with people having lavalier mics clipped on. Oftentimes, they will have their cell phone either in their pocket or resting on the table in front of them.

Maybe it's not possible to get rid of 100% of all of the interference, but it seems like some mics do a much better job than others. For instance, we have some Lectrosonic wireless pairs (not sure the model) that don't seem to ever pick up any type of cell phone noise.

Since I posted this, I've been doing more research, and I might be even answering my own question. It seems Shure has a microphone, the MX150, which is supposed to have some form of EMI / RF guard or shielding. I also was reading about Audio Technica and their "UniGuard" shielding, which seems to be essentially the same thing.

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

Black Berry and other extraneous rapid beeping type noise are often induced though a mic cable. Try replacing the cable with a star-quad design, from Canare, Belden or Mogami. before spending $3k on a Lectro system.,.. though a Lectro is a good gear investment

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

Thanks for the suggestion, Rick. Could you give me some info on where I could find one of those star-quad designs you're talking about? I don't think I've ever heard of them.

The Lectros do work well, but I'd rather not have wireless mics, mostly due to having to swap out the 9V batteries every now and then.

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

I should add that it appears the interference/noise is coming in on the thin wire between the actual microphone itself and the power pack. Everything seems okay from the XLR cable on, so it seems the vulnerability is with that thin microphone cable.

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

Typically a lav is unbalanced so it's not surprising the the culprit woulds be the cable between the mic capsule itself and the power supply/balancing transformer/XLR adapter.

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

With that in mind, I wonder if there's anything I can do to mitigate the damage or lessen the intensity.

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

Yes - insist all mobile phones are switched off or set to "Airplane Mode" while you are recording.

This is standard in all professional recording situations.

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

Right... I already ask them to do that.

The problem is, these are depositions in conference rooms, so it's not your standard professional recording studio/set. People fall into old habits, or they just don't comply thinking that it's not really necessary to have the radios fully off.

With that in mind, I'm trying to find a way around that. And like I mentioned, some microphones DO seem to deal with it much better than others, so it's just a matter of finding the right equipment/retrofitting my own to work better.

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

If you are doing depositions...
A) Do everybody a favor and skip the wireless mics. They are more trouble than benefit in this scenario.
B) Leave it up to the attorneys how serious they are about having interference-free recordings.

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

I know wireless has its advantages, but I was also kind of hesitating to use them. Here are the cons, as I see them:

* Possible static/interference over the air
* Having to swap out/charge batteries
* The risk of somebody forgetting to take it off when leaving the room

The benefits, on the other hand:

* What seems to be better resistance to cell phone interference
* Tidier. Not having to string cables all over the place.

Anything else that I'm missing?

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

NEVER EVER use wireless when you can use a wired microphone! Depositions are a perfect example.

A solid-gold $10,000 wireless microphone can NEVER EVER be as good as an ordinary $20 cable! In any and every situation.

A wireless microphone is ALWAYS a 2nd choice compromise over using a wired microphone.

Wireless microphones are MUCH MUCH *MORE* susceptible to cell-phone interference. I have thousands of dollars worth of wireless mics that have been rendered useless in places where cell phones cannot be controlled.

I would NEVER bring a wireless microphone to a deposition shoot.

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

There is a reason broadcast mixers go hardwired most of the time. Unless mobility is a necessity...wire works!

Let me add, a balanced mic into a balanced input on a recorder will be your best defense against RFI.

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

XLR is always balanced... right? I go XLR from the mic to the mixer, then XLR from mixer to recorder (camera).

If that's true, then how would I go about finding a balanced microphone itself? Are there certain specs I can look for?

Also, aside from forcing people to actually shut their phones off, have you guys found any tricks at all to minimize the problem? In my experience, it seems like some mics handle it better than others, so I guess I'm wondering if anybody has any recommendations on actual mics or anything I can do to with my existing equipment.

Thanks for chiming in!

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

The snag with interference of this nature is that there are two main ways it gets into the system to cause problems. The first is that the mic cable acts as an aerial - the screen feeding the interference to the mixer/pre-amp input where it causes problems. Secondly, it gets to the inner conductor(s). Radio microphones don't need mics with balanced connections, as they power the mic by applying the polarising voltage superimposed on the audio line, or my putting the voltage on a separate core. In most cases, even when a lav mic has an XLR connector, it's often one of those extra long ones, with the pre-amp in the plug - so although it has balanced output, the input may well be unbalanced - and therefore more susceptible to the stray RF currents. Solving these issues is always difficult because the RF noise is unpredictable, but my own experience is that some mics, usually the ones commonly used on wireless systems that have unbalanced cabling, are the worst. If you need the RF immunity then you'll have to set up some tests to establish which items you have that are contributing to the problem. Some input devices seem more prone to the problem. An AKG I use from time to time is totally fine when plugged into a Yamaha mixer, but the same mic plugged into a JVC camera is prone to the problem. I'm certain the issue is cable pickup, but a mic input with poorer RF rejection characteristics. Lots of trial and error to find combinations that work better. I'm not sure you'll ever cure it. I had the problem a few days ago when I left my own phone on my macbook, that had the headphone output connected to the usually good Yamaha mixer. I guess the phone on the aluminium chassis of the macbook allowed the RF to travel straight down the cable into the mixer - and the nasty noises emerged! I have an old transformer isolator and using this, which has an output with no direct wired connection to the input socket, does work to be a good isolation device. Difficult to use one of these on every input, though. probably a step too far, but could you use ordinary microphones on desk stands? Properly balanced and more reliable?

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

As several people have stated, this problem most likely comes from the use of an unbalanced mic and wiring at some point in the chain, as is the case with the small electret lavs. For all we know, in some cases the interference might actually get into the high impedance FET which is part of the electret mic capsule itself.

Seems to me that the most trouble-free solution would be to use a balanced dynamic mic, rather than an electret. The mic element itself is low impedance, it's purely passive (no onboard FET), and you feed a balanced signal down a twisted pair (with a shield, of course) directly to the recorder. If the recorder is properly constructed, so as to be RF-immune itself, the problem should disappear. (A transformer-coupled input would be better than an active balanced input, IMHO.)

Of course a dynamic lav is a bit larger than the smallest electrets. But you're not micing a broadway musical, and you don't need to hide the mic in someone's hairline. A visible mic is perfectly OK for depositions.

If I were in your shoes, I'd try something like this: Shure SM11CN Omnidirectional Dynamic Lavalier Microphone | Full Compass

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

not always...many devices that use XLR connectivity are actually unbalanced circuits. Real balanced circuits cost more so it's usually the cheaper devices that are unbalanced. hard to know for sure without looking at circuit diagrams or plain old testing as manufacturers aren't usually given to divulge the inner workings anymore. if you can read a dead short between pins 1 and 3 of an input it is most likely UNbalanced.

I will say that we use senn mke-2 (def unbalanced mic) and sony ecm-77or88 (not sure about balanced) and rarely have issues, but again the source is only half of the equation. I do know the desks i use (calrec, yamaha, SSL, Neve) all have true balanced inputs (active), and many have transformer coupling to boot.

Easy way for you to test, make a call to your own mobile. while it is in call hold it next to your mic. During the call is about the most active rf signal the handset will produce and it continues as long as the call is in progress. If there is going to be a problem with interference this will decidedly reveal it.

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

All mini tie mics are unbalanced down the cable - they are balanced at the XLR connector.

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

Not quite.

All electret mini tie mics are unbalanced down the cable.

The Shure which I referenced above (Post #17) is a dynamic, and according to the literature and wiring diagram it is a conventional balanced dynamic mic. Nothing unbalanced about it.

Of course it's not quite as "mini" as some of the electrets but it's still small enough to be used with a tie clip.

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

I e-mailed Audio Technica to ask about any possible way to retrofit the AT803B to resist the interference.

The response I got was a suggestion to use an inline RF filter, such as this Shure A15RF: Shure A15RF RF Filter, Problem Solver | Full Compass

I wonder if that would do the trick! Seems very intriguing. Anybody have any experience with one of these?

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

Unlikely to work. Reason: The RF is getting in to the INPUT end of the mic and filtering the OUTPUT of the microphone won't get rid of the interference after it is embedded into the audio.

My policy is: If the attorneys aren't concerned enough about the problem to order everyone to turn off their cell phones, then it is NOT YOUR PROBLEM. Leave it up to the customer how serious they are.

It MAY be possible to "RF-harden" that microphone, although I would bet against it. But the A-T people know that if you have to ask, you aren't qualified to perform the modification. Not to mention that there is almost nothing you can do that won't instantly void the warranty and carry a good likely hood of destroying the microphone in the process.

The one thing that has a (very small) chance of success would be to use an external ferrite bead filter around the mic cable. Unfortunately, these are typically much larger than the microphone themselves and would render the microphone horribly clunky, ugly and difficult to use. And they still wouldn't work if the RF path is directly into the microphone head which is the most likely problem.

As others have already suggested. If you really MUST operate in an RF-hostile environment, use old-fashioned fully-balanced dynamic microphones with good shielding. And maybe some of those Shure RF filters as well.

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

Do they have balanced dynamic microphones that are lavaliers? Or is there some reason not to be using them?

This video is really interesting:
I wonder if soldering some of those X2Y capacitors onto the mic's circuit board itself would help.

Thanks for all the feedback, guys.

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

Yes, this was already suggested in previous responses. Did you just blow it off?

Dynamic mics are larger and not as sensitive as electret. They are also a dying breed.

Yes, it would be interesting if you were Audio-Technica. But there isn't anything you can do retroactively as an end-user.

Yes and No.

Yes: If you could get them into the right spot, they would protect the very sensitive FET gate against RFI. But I guarantee that there isn't enough room on the board to put ANY of those components.

No: Adding capacitance across the input will attenuate the very tiny audio signal and make the problem worse because it will tend to DECREASE the signal-to-noise ratio (SNR). An electret microphone is a very special kind of circuit that is very difficult to protect against nearby GSM pulse-mode RFI.

Repeating: If you want to use electret microphones you MUST turn off the phones in the room!
If you can't do that then you have a choice of using an old-school balanced dynamic mic, or else just living with the interference. You aren't the first to encounter this problem. You aren't even the 1000th. You seem to continue to believe there is some magic solution. Rest assured that if there were a magic solution we would have all heard about it by now.

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

I read the bit about dying breed and thought 'rubbish', but it's quite right - I had an old AKG which I quite liked, but a bit of Googling showed that in reality - we have a single Shure and a single EV microphone - neither of which are very small - the EV for example, is 3/4" in diameter, so hardly tiny.

The X2Y products (wasn't that a dreadful video?) seem to be pcb based, and it's a shame they haven't produced one built into an XLR-XLR barrel type connector that could be plugged in line.

I guess we're just going to have to accept that phones DO have to be off.

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

I said mini tie mics - the Shure is not a mini tie mic.

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

The interference has already been embedded into the audio by the time it reaches the XLR output connector. There is NOTHING you can do by the time it reaches the XLR connector. I you don't prevent the RFI from getting into the very first stage (the impedance converter circuit inside the head) it is TOO LATE.

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

"What's in a name?"... I guess it depends on your definition of "mini."

The first dictionary I grabbed says:
miniature: "-adj., on a very small scale, reduced"

miniaturize: "v.t., to reduce in size"

While the SM11 is certainly not as small as the newer electret tie mics, it is "reduced in size" compared with a lot of the earlier lavs that we saw in past years. The sizes have gotten progressively smaller, and perhaps we're near the end-point of the curve with the SM11.

Shure SM11: L = 33.5mm, D = 14.7mm.

EV 649B: L = 57.2mm, D = 19.0mm.

Shure SM51: L = 62.7, D = 19.8mm.

EV RE85: L = 67mm, D = 23mm.

Altec 686 (ugh!): L = 88.9mm, D = 27mm (max).

Shure certainly expects the SM11 to be used as a "tie mic" as the spec sheet indicates it ships with a "Tie Clasp Assembly" and a "Tie Tack Assembly." Admittedly, I wouldn't want this thing hanging from a pin shoved through my necktie. Then again, I don't remember when I last saw my necktie.

So I think it's accurate to say that the SM11 is a "tie mic" and, given that it's the smallest dynamic I've found, it might be called "mini" as well. But, ya know, if it makes everyone happy I will call it a "small" dynamic tie mic.

BTW I note that the Shure/Countryman WCB6T (electret) is described as a "Micro-Lavalier Microphone" so perhaps we've now reached a new "micro" dimension which is smaller than "mini."

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

And remember that even a balanced dynamic microphone may be susceptible to GSM RFI, depending on how it is designed and constructed, and depending on the connectors, cabling and microphone preamp.

There is no guarantee that there is ANY microphone that is truly "impervious" to GSM RFI.

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

Absolutely correct!

If the dynamic capsule is insulated from the case, it is pretty much balanced... that's a function of capacitance between the capsule, the case, and the microphone coil. At typical lo-z mic impedance (~ 200 ohms) and audio frequencies, any imbalance should be so small as to be insignificant; at RF it becomes more important.

A shielded twisted pair should be pretty much impervious to the RF levels we're talking about. But some shielding is better than other shielding... you need to check the wiring specs to find the percentage coverage of the shield. (This is especially important for RF coaxial cable.)

Still, a bad input stage (mixer, preamp, recorder, etc.) can cause problems. If the case and pin one connectors (of the XLR) do not connect immediately to the chassis where they enter, but rather follow some long "ground" wire to the circuit board, that "ground" wire will act as an antenna, and will re-radiate any RF (which was picked up on the shield) back inside the chassis, where it can easily bleed into everything.

Still, the OP said he had problems only when the phone was near the unbalanced cable, between the capsule and the connector, and not with the cable from the connector to the preamp. If that is truly the case, then I feel pretty confident that a balanced mic (like the SM11) would solve his particular problem.

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

That sounds encouraging.

I might have the terminology wrong, but here's the explanation in layman's terms:

The microphone itself (with the tie clip) has a thin wire that connects to the power pack. The power pack then outputs via XLR to the mixer.

The noise does not seem to come in on the XLR cable -- only on the thin wire between the microphone and the power pack. The intensity does not seem to vary if you slide the phone up or down this thin wire, leading me to believe that it's not necessarily the microphone itself, but just this thin wire that's picking up the noise.

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

There is a (small) possibility that you can filter out the RFI using a ferrite bead aound that thin mic cable. The most effective would be to put 3-4 turns through a ferrite torroid, but that would be pretty clunky with a torroid big enough to pass the microphone head through. Or you could try some of the "snap-on" beads like those on this page...

Ferrites | AllElectronics.com

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

Interesting suggestion, Richard. Your suggestion about several turns of mic wire through the ferrite is absolutely correct, and the snap-on type would make that easy to implement. FWIW, I've ordered from All Electronics before, they're reputable.

RF is very strange, in that it travels on the outside surface of a conductor, and does not penetrate to the inside. When cellphone RF intercepts the shield on the mic wire, it travels mostly on the outside of the shield. Ferrite acts like a low-pass filter, stopping the RF from traveling any farther along the wire. Using ferrite, as close as possible to the point where the wire enters the preamp or bodypack, would prevent [a lot of] the RF from continuing along the shield and into the preamp.

As you point out, there are still other ways that RF can get into the audio. But if the OP is really in love with his present mics, investing a few dollars to try some ferrite is certainly a worthwhile experiment.

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

I do depositions for a living and only a couple of times encountered cell phone interference out of hundreds of depos. If there's a cell phone issue you politely ask for the phone to be shut off or moved away from the mic. I think you're making to much of this and like others have said wireless is a bad idea. One last thought this issue could be due to something else. Have you ruled out your mixer? What are you using for a mixer btw?

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

My mixer is a SignVideo ENG-44.

I'm fairly positive the mixer is not the issue. It appears that the only point of entry is between the microphone itself and the thin wire that connects the microphone to the power pack

If you don't mind, Pete, perhaps you can share what kind of microphones you use. I'm definitely open to buying new mics that handle the interference better.

It's not always a big deal, but sometimes somebody may have an iPhone in a shirt pocket just inches away from the mic. In a case like this, if there's a lot of phone activity, it can seriously mess with the audio.

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

There are a great many situations where people (participants, audience, etc) are asked to turn off their cell phones. I would think that a formal legal deposition would certainly be a place where the attorneys would be concerned about having the uninterrupted attention of the deponent or witness (as well as everyone else in the room). I am rather surprised that this is even a problem at all. If the attorneys didn't ask for cell phones to be turned off, as the videographer, I would take the initiative and state the conditions for proper behavior.

No electret microphone is immune from interference from a cell phone mere inches away.

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

I don't do depo's but I do live television, web streaming and convention/conference work and MOST people seem to think "turn OFF your cell phone" means "turn it to vibrate or silent". I have ACTUALLY been told by speakers that "this is good enough and that's all I'm going to do".

Again, in a legal deposition, you may well have more influence but I can attest to TRYING to do the right thing and having been thwarted. Not once or twice but DOZENS of times.

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

In that case, the production decision has been made by others, and any cell phone interference was pre-authorized by the "producer" so it is no longer my concern. End of discussion.

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

I understand it might not technically be my fault if somebody refuses to shut their phone off or thinks I want them to only turn the sound off, but I guess I'm more concerned with the end result.

It seems like some pieces of equipment deal with the GSM interference better than others, so my goal is to just give myself the best chance possible to have a clean audio feed, knowing that it's not always doable to have all the cell phones off all the time. Knowing how attached people can get to their phones, I sure would love a way to not even have to make that an issue for people.

Again, thanks for all the input, guys!

Re: Looking for a good lavalier mic that is impervious to GSM / cell phone interferen
 

This whole issue -- turning off every phone, whose job it is to enforce the rule, and who is responsible if someone doesn't comply -- may be an interesting philosophical discussion, but it's not a technical solution. Why belabor the point?

Everyone knows you're recording a deposition. You don't need a "micro-mic" that's nearly invisible. Get the mic that is technically right for the job, and you can forget all the other issues.

Then get the SM11 dynamic, which is fully balanced, and you should never have to think about cellphone interference again.

Any electret will be susceptible to some degree... you'll never know how much until it's too late. Do you want to make this an endless research project, or do you want to have clean audio every time? If the latter, just get the SM11 dynamic and get on with recording. My gosh, they're only $100 at B&H, it doesn't get any better than that.