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Old October 11th, 2005, 05:42 PM   #1
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Cell Phones & Mic Interference

Had an interesting thing happen the other day. I own a GS400 and a Rode Videomic. I was out in the field recording, when at times, I heard a strange quiet but noticeable beeping/clicking sound in my headphones as I monitored my audio. It sounded somewhat familiar, but I thought I might have been having toruble with my mic or my cam with the electrical lines overhead or something.

It wasn't until the next day, while writing an email on my computer, that I heard the exact same sound coming out of my computer speakers. Then, it hit me. It was my freakin' cell phone. I had heard that noise from my cell in my speakers before, but I didn't make the connection that that was the same noise coming through on my MiniDV recording. What's interesting is I just got a new cell phone recently, and I upgraded to GSM from TDMA, and I've noticed that it "communicates" on it's own every once in a while, much more so that my previous TDMA phone did (that phone only made the noise when receiving a call, my new phone does it entirely on its own sometimes). Besides the obvious cancer-causing sketchiness this makes me wonder about, it also now has me needing to turn off my phone altogether when recording so as to ensure I don't pick up the interference. But, man, everyone and their brother has a cell phone these days, and it makes me worried that no matter what I do, I might pick up this interference at times -- it's subtle, but noticeable.

Anyway, I was wondering a couple of things from the crew around here: (1) have you ever run into this problem yourselves? And (2) am I picking up this noise because my Rode Videomic is has an unbalanced connection to my cam? Would an XLR mic going into a cam that had XLR inputs pick up this sound/interference?
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Old October 11th, 2005, 05:58 PM   #2
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You aren't the first to have this happen. There is a thread from a few months ago that raised the same issue.

The new phones do more 'communicating' on their own than the previous ones did. Most of it is your phone on the constant look out for the strongest cell tower or any cell tower if you are in marginal coverage. Other enabled features can also necessitate the phone communicating with the network.

And btw, the other thread was based on the corporate participants in the videotaped meeting having their cell phones on and killing the audio. Fully balanced and shielded XLR audio cables may help, but there are likely other routes of entry for the interference.

But to summarize, yes it's a well known phenomenon.

-gb-
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Old October 11th, 2005, 10:36 PM   #3
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Quote:
Originally Posted by Bill Binder
Anyway, I was wondering a couple of things from the crew around here: (1) have you ever run into this problem yourselves? And (2) am I picking up this noise because my Rode Videomic is has an unbalanced connection to my cam? Would an XLR mic going into a cam that had XLR inputs pick up this sound/interference?
Welcome to my GMS nightmare! I had the exact same experience when I first got my GSM phone. I couldnít track it down and I was ready to blame my neighbors. Then I was in a conference call at work and the same sound came over the conference phone. Thatís when it hit me that I was the common denominator. It wreaks havoc with any electrical equipment. If Iím in the kitchen pouring a cup of coffee, it interferes with the kitchen radio. I keep my phone off when I do any audio recording. It was the only solution.

~jr
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Old October 11th, 2005, 11:10 PM   #4
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it affects all microphones, even the expen$ive ones. try telling a national sports network announcer he has to turn off his cell phone because the interference from it is on the air...sometimes it's from someone whom you have no control over. all you can do is move away from it.
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Old October 12th, 2005, 08:40 AM   #5
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Yes GSM, especially Cingular GSM are very nasty about this because of the frequency hopping spread spectrum technolofy and the fact that the radio "stays in touch" with the network pretty frequently. My Moto V180 is my new enemy (and friend). Just turn it off at critical times.
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Old October 12th, 2005, 11:16 AM   #6
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Alright, seems so obvious now. Doh! And, yes, I am on Cingular GSM. Lucky for me, the times it happened weren't during dialog, so it was an easy to fix lay in some ambiant noise from other clips I had, but damn, the thought of taping in a convention center or something like that makes me cringe now. Thanks for the replies. I first thought my mic was on the fritz, but once I heard it on my speakers I immediately knew what was up.
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Old October 12th, 2005, 01:38 PM   #7
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I don't believe it's limited to any one carrier. I currently have a GSM phone, and yes it interferes with just about any kind of audio equipment within 6-10 feet (for that matter, I get flickering lines in my CRT monitor if it's right next to it!). I work in an audio industry where we are constantly running into people with phones on.

It's not just phones either. Pagers, blackberries(tm), or anything that uses the GSM or GPRS network can be a culprit. Silent mode doesn't cut it -- they have to be powered off completely.

My older digital phone (pre-GSM) also caused interference, but it was more like a series of low-frequency pops and was not nearly as potent. Even WiFi networks can potentially be a problem. Anything wireless has the capability to interfere.

Do we have any European readers that can weigh in on this? I thought I heard that GSM has been the established cellphone technology over there for quite some time now. How do you guys cope with it?
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Old October 13th, 2005, 05:01 AM   #8
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Jeremy: yes we have had GSM here in Europe for many years now. But it's on different frequencies than you use in the US. In Europe it's the 900MHz system. (I believe it is 1800 and/or 1900MHz in the US)


I have only a few times noticed the interference. Most of the time, I don't have any trouble. Even if I have my cell phone in a chest pocket, when shooting handheld. (I use a Canon XM2)
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Old October 13th, 2005, 08:10 AM   #9
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Quote:
Originally Posted by Trond Saetre
Jeremy: yes we have had GSM here in Europe for many years now. But it's on different frequencies than you use in the US. In Europe it's the 900MHz system. (I believe it is 1800 and/or 1900MHz in the US)


I have only a few times noticed the interference. Most of the time, I don't have any trouble. Even if I have my cell phone in a chest pocket, when shooting handheld. (I use a Canon XM2)
You are right about the difference in frequency between US and Europe. However, we are able to buy phones here that have all three bands so they can work in Europe as well.

But to keep this on topic, just try to maximize distance from any powered on cell phones or keep them turned off.

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Old October 13th, 2005, 10:50 AM   #10
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Looked on the net and it seems that here in Japan we don't use GSM, but we still turn off our cell phones when we have a video shoot, we get the same interference when a call or email comes in. Same with having my cell phone next to my computer speaker, I can hear the speaker buzzing a second before my phone rings.

At first I thought my camera needed to be serviced, I took it in one time(XL-1) because I would get that buzzing noise sometimes, Canon ended up replacing the heads for free so I can't complain, but now I know the cause of that noise.
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Old October 13th, 2005, 10:21 PM   #11
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What we learned in that other thread was that mics often and (mixers sometimes) have a grounding error. This is a careless design error where the cable runs through the metal housing of a device and the cable shield is connected directly to the circuit ground of the electronics. A little wire is run from that point to the metal housing so that it is grounded too. Trouble is, at high frequencies that little wire has significant impedance, so there is a voltage across it and it acts like a "trojan horse" antenna broadcasting interference to the electronics you thought were protected by a grounded housing.
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