Cell Phones and Microphones?

[Ken K]

Has anyone had any experiences with cell phones causing interference with microphones? I recorded a concert at a private home for a songwriter with a small group, gtr, bass, drums / perc, viola, cello, flute, clar / oboe, the songwriter sang and played piano.

Recorded the rehearsal the night before and no problems but the next night on the gig with about 80 people in the audience the mic I used on the flute/oboe (TLM 170) would intermittently start to buzz sort of like morse code. First I thought it was the mic chord but I was using identical cables on all the mics. Got through the gig with no train wrecks and started to investigate because I thought the mic had a problem.

When I started asking around about where to get the mic looked at a couple of engineers said the mic was probably fine and it sounded like cell phone interference. That was the only mic that had a problem. Other mics I used were 2 KM84, 2 TLM 193, 1 TLM 103, 2 Sennheiser 8040, 2 Sennheiser e609,1 Sennheiser e604, 1 Sure beta 52. One engineer said he's had that come up a lot on orchestra dates with certain microphones. Makes me think TLM 170's are very susceptible. Anyone had similar experiences?

[resound]

Originally Posted by Ken K

Has anyone had any experiences with cell phones causing interference with microphones? I recorded a concert at a private home for a songwriter with a small group, gtr, bass, drums / perc, viola, cello, flute, clar / oboe, the songwriter sang and played piano.

Recorded the rehearsal the night before and no problems but the next night on the gig with about 80 people in the audience the mic I used on the flute/oboe (TLM 170) would intermittently start to buzz sort of like morse code. First I thought it was the mic chord but I was using identical cables on all the mics. Got through the gig with no train wrecks and started to investigate because I thought the mic had a problem.

When I started asking around about where to get the mic looked at a couple of engineers said the mic was probably fine and it sounded like cell phone interference. That was the only mic that had a problem. Other mics I used were 2 KM84, 2 TLM 193, 1 TLM 103, 2 Sennheiser 8040, 2 Sennheiser e609,1 Sennheiser e604, 1 Sure beta 52. One engineer said he's had that come up a lot on orchestra dates with certain microphones. Makes me think TLM 170's are very susceptible. Anyone had similar experiences?

Certain cell phone techs cause this: not the CDMA that Verizon runs on, but GSM networks like AT&T, T-Mobile, etc.. This is actually a pretty well documented issue. Sadly, I don't have a good suggestions other than to make sure all phones are off.

[kwesloh]

Usually it's just the mic that's closest to cell phone that exhibits. I've had this happen with B&K 4006s, KM-184s and AKG-422s. In almost every case they have been hanging over an audience.

-Kyle

[Beech]

I've only ever noticed this when I leave my phone on the console. Any chance that might have happened?

[Remoteness]

Originally Posted by VukOnCrack

Certain cell phone techs cause this: not the CDMA that Verizon runs on, but GSM networks like AT&T, T-Mobile, etc.. This is actually a pretty well documented issue. Sadly, I don't have a good suggestions other than to make sure all phones are off.

Yes, completely off, not just on vibrate! I've found that some musicians don't understand this concept.

[Remoteness]

It's not just with microphones, but with many other electronic devices, like Beech mentioned above.

Move an active GSM cell phone around your CRM and listen to the noise the phone makes.

I even heard it on one of the Grammy telecasts when U2 was excepting their award.
Someone must have had their phone on while at the podium.
It was live television and there was no going back.

Part of the recording process should be to let all musicians know they must turn their phones completely off.
In many cases we let the audience know this too, not just for the potential noise problem, but for the fact that we don't want a call coming through during the recording... Ouch!

Originally Posted by Ken K

Has anyone had any experiences with cell phones causing interference with microphones? I recorded a concert at a private home for a songwriter with a small group, gtr, bass, drums / perc, viola, cello, flute, clar / oboe, the songwriter sang and played piano.

Recorded the rehearsal the night before and no problems but the next night on the gig with about 80 people in the audience the mic I used on the flute/oboe (TLM 170) would intermittently start to buzz sort of like morse code. First I thought it was the mic chord but I was using identical cables on all the mics. Got through the gig with no train wrecks and started to investigate because I thought the mic had a problem.

When I started asking around about where to get the mic looked at a couple of engineers said the mic was probably fine and it sounded like cell phone interference. That was the only mic that had a problem. Other mics I used were 2 KM84, 2 TLM 193, 1 TLM 103, 2 Sennheiser 8040, 2 Sennheiser e609,1 Sennheiser e604, 1 Sure beta 52. One engineer said he's had that come up a lot on orchestra dates with certain microphones. Makes me think TLM 170's are very susceptible. Anyone had similar experiences?

[GYMusic]

I doubt that the TLM-170 was at fault. Most likely a cable. Cell phones do not emit RF when they are on standby. And, when they are on and transmitting, the RF frequency is so high and at so low of an RF level, it would not be a problem for a microphone.

[LX3]

I find that cell phones break thru into unbalanced lines extremely efficiently. I occasionally get a scare when I hear one during a recording, but it's always turned out to be interference picked up by my Roland M240R, which is all unbalanced. So that racket doesn't make it to tape thank heavens.

I had a bit of an argument with a punter at the Jazz Cafe once, who insisted on making calls and sending texts right next to my rig. Deafening racket. I was like "I'm not being funny, but could you switch your phone off? - I'm getting interference". His answer was "How can you possibly hear me over the band?". That turned into a long and frustrating conversation.

I haven't had any interference from cell phones into microphones or mic lines... but that's not to say it can't happen. The bit of microphone from capsule to impedance converter is basically unbalanced... if very short.

I'm not using the Roland any more, so now I can tell the difference between noises that I'm recording and noises that my monitor desk is making...

[Jim vanBergen]

I've been working with two manuacturers on the R&D for solutions to help combat this problem. In reality, high power RF devices (yes, a cell phone is MUCH more high-power than a simple wireless microphone!) emit huge amounts of RF (I have measured up to a watt or more when in a data handshake with a cell tower!!!) which will completely obliterate any signal you have that is travelling down an unbalanced path. Now, where will you have an unbalanced signal path? Any cable with a short or shield bonded to case, and in many parts of a simple audio circuit, from the capsule to the transformer. Most podium mics, most lavalier mics, most high end microphones have an unbalanced signal from capsule to active electronics and again thru transformer. Most active electronics in a microphone utilize an IC to quasi-balance the audio circuit.

Even if you have great signal integrity from the stage side, I have been my own culprit by leaving on my blackberry while mixing on a DiGiCo and hearing it blast thru the console. Just a reminder that it's not only microphones but everywhere in a signal path and we have to be incredibly vigilant to maintain signal integrity.

Cheers!

JvB

[Ken K]

Originally Posted by Jim vanBergen

Now, where will you have an unbalanced signal path? Any cable with a short or shield bonded to case, and in many parts of a simple audio circuit, from the capsule to the transformer. Most podium mics, most lavalier mics, most high end microphones have an unbalanced signal from capsule to active electronics and again thru transformer. Most active electronics in a microphone utilize an IC to quasi-balance the audio circuit.

JvB

Jim,

Two questions: 1) not quite sure by what you mean, "shield bonded to case"?

2)"most high end microphones have an unbalanced signal from capsule to active electronics and again thru transformer" - Do you mean within the microphone before it even gets to the mic cord?

One more question. Would a mic cord with the shield floated at one end be more resistant to RF then one with the shield connected at both ends? I thought I had read an article about wiring patch bays using that method.

[Cosmic Closet]

Working a lot of corporate video for a living, I can't count the number of times a cellphone has done its thing in the middle of an event.

Whether a long, low buzzing, pulsing sound or the classic "motorboating" effect of a Nextel, those things can and will screw up audio.

At least we seem to be done with the Nextel Walkie-Talkie option. One of those keyed near a Betacam recorder (or any other kind of analog tape) would punch a hole in the recording if you were unlucky.

Best,
Claus.

[Jim vanBergen]

Originally Posted by Ken K

Jim,

Two questions: 1) not quite sure by what you mean, "shield bonded to case"?

2)"most high end microphones have an unbalanced signal from capsule to active electronics and again thru transformer" - Do you mean within the microphone before it even gets to the mic cord?

One more question. Would a mic cord with the shield floated at one end be more resistant to RF then one with the shield connected at both ends? I thought I had read an article about wiring patch bays using that method.

Answers:
1) on an XLR cable, the ground (pin 1) should NEVER, EVER be bonded to the metal connector. However, I often find that they are. The older Switchcrat connector is the most common connector where I see this problem, the new Neutrik XLR - never. That can be the cause of a ground loop within a system that exhibits classic grounding problems.

2) a capsule is two wire (unbalanced). Open a LDC and look at the capsule- +/-, going go the circuit. And from the circuit to a transformer, usually the same- just two wires, +/-, like in the classic Shure dynamic designs. So this is the first place that some designs ail in terms of RF integrity, and where the consulting I'm doing with mic manuacturers is directed.

3) lifting the ground on an XLR cable is a BAD IDEA. What you mention with patchbays is common or electrical contracting, in which large number of wires are all ground lifted at the same place- all at the patchbay side. I have seen this work well, and also I have experienced this as the basis or classic "pin 1 problems" with some installations.

Phiilip Giddings wrote an excellent book on this topic, Jim Brown (a member of the AES) has also written some excellent white papers on the topic- there is a lot of good information out there for those who are interested in learning more.

JvB

[videoteque]

A microphone with a metallic body should be safer, if the metal sourrounds everything it should shield from external "waves".

If you have 100 people, you will NEVER get all of them to switch their cellulars off...

[Jim vanBergen]

Originally Posted by videoteque

A microphone with a metallic body should be safer, if the metal sourrounds everything it should shield from external "waves".

If you have 100 people, you will NEVER get all of them to switch their cellulars off...

I wish that were the case, but sadly it's not. Vintage Neumann microphones are often HIGHLY susceptible to this problem. By the same token, most mixing consoles are folded steel...which is also not strong enough to shield the internal electronics.

[locosoundman]

This may be a myth, but I have heard that transformerless (mic) designs are more susceptible to RF interference problems. Anyone know whether or not this is true?

[Testing123]

Originally Posted by Ken K

Recorded the rehearsal the night before and no problems but the next night on the gig with about 80 people in the audience the mic I used on the flute/oboe (TLM 170) would intermittently start to buzz sort of like morse code.

It's not impossible that you were really hearing morse code. There are still ham radio operators using morse code, and if there happened to be one nearby your equipment could have been getting RFI from that.

When audio equipment is interfered with by equipment using RF, it's almost always a design problem on the part of the audio equipment. People tend to blame the RF equipment (and it's true that if you turn it off the problem goes away) but if the audio equipment was designed properly there would not be an issue. The RF equipment is doing what it's supposed to do - radiating RF.

[jacobfarron]

I haven't read all the replies, but Neutrik makes the EMC-XLR connectors (male and female) that filters most interference from cells and RFI. For critical situations (like the live shots I do for networks) they're the best. No problems since I've installed them. Neutrik - Audio - EMC-XLR Series

[zoff]

Originally Posted by jacobfarron

I haven't read all the replies, but Neutrik makes the EMC-XLR connectors (male and female) that filters most interference from cells and RFI. For critical situations (like the live shots I do for networks) they're the best. No problems since I've installed them. Neutrik - Audio - EMC-XLR Series

I tried them at the inputs of my powered monitors and at best they only lowered the level of interference from my phone. Do you have the connectors at both ends of the cable? I only wired them to the male XLR at the speaker amp inputs.

[Jim vanBergen]

Originally Posted by zoff

I tried them at the inputs of my powered monitors and at best they only lowered the level of interference from my phone. Do you have the connectors at both ends of the cable? I only wired them to the male XLR at the speaker amp inputs.

The Neutrik and Gepco cables that are sold with the new ferrite-enhanced connectors utilize them at both ends of the cables. I'd be VERY concerned if I did not use them at the female (microphone) end.

[David Rick]

The Time Division Multiplexing scheme used by GSM phones, Blackberry's and what have you is very, very difficult to keep out of low-level mic lines. When K2 Audio redesigned the PA for the U.S. Senate, they had to work really hard at this. (Jim, you might see if Ray Rayburn would be willing to talk with you about what they did.)

Those who lean toward the geek side of things (probably those with an EE degree) may want to look at these powerpoint slides from Henry Ott's master class at the AES convention in NYC last fall.

David L. Rick

[jacobfarron]

I use them at both ends. After extensive testing on one of our sound stages, I found the cable to the mic has the most chance of interference. But I use them throughout the chain: mic to mixer, mixer to recorder or camera or vyvx fiber. I spoke to our Neutrik rep and he told me specifically that both connectors need to be use to realize the full potential of the noise blocking.

They're a bit pricey (about $10 to $15 per connector) but well worth it IMHO. I can't speak for others, but when we're on live and some frantic director across the country is yelling in the PL I want to make damn sure I don't give him anything else to yell about.

And, as I said... no problems since.