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Author Topic: cell phones in the studio.  (Read 6069 times)

Offline j.hall

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cell phones in the studio.
« on: May 12, 2004, 05:04:12 pm »
this keeps hapening to me i need some ideas of what to do

i'm rolling tape, some one's cell goes off and now i have this static all over the track

i'm recording to 2" 24 track....and all the new cell stuff get's picked up on the head stack......what the hell?

it's nasty too

it get's into the console, monitors

makes me wonder if it'll screw up the tape when i'm simply in playback

or if some one sets their phone on a reel box and it rings.....YIKES


Offline spankenstein

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Re: cell phones in the studio.
« Reply #1 on: May 12, 2004, 08:51:00 pm »
I'm definitely not an expert on tape but cell phones work like a radio essentially. Nothing magnetic other than the speaker and I think that's too weak to do anything to tape.

I have noticed that GSM phones (t-mobile, at&t) make funny noises that often get picked up buy guitars before they ring and periodically when they "chat" with the tower.

Offline j.hall

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Re: cell phones in the studio.
« Reply #2 on: May 13, 2004, 09:27:25 am »
i'm on cingular, and my tracking engineer is on PCS

if we are rolling tape, "in record", and one of our phones' rings.  we get all sorts of strange static on the tape deck.

this is at his house (where all the mix room gear currently lives) and at two studios in town.  

at first we thought the issue was isolated to his house since the deck is in very close proximity to where we are sitting.

but then it happened at a studio with a machine room about 20' away from the tape deck remote, and at another room with the deck about 8' away.

i can't risk this noise printing itself randomly to tape

does anyone know anything about this....do i just turn all cells off?


Offline josh

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Re: cell phones in the studio.
« Reply #3 on: May 13, 2004, 10:31:17 am »
Nothing magnetic?  Are you kidding?

The whole way a cell phone operates is with electromagnetic/electrostatic wave transmission.

When the phone transmits, there are two "fields" produced by the antenna and also by the amplifiers and other circuitry in the phone:  "H" field or "magnetic" field, and "E" field or "electric" field.  

The "E" field is used for radio transmission.  Your gear is unlikely to pick this up, and even if it did, it's happening at nearly 1 gHz so you can't hear it.

The "H" field is useless for radio transmission because the intensity of this field is reduced at a rate of the inverse of the cube of the distance.  So this means the field is 1/8 as strong at 2 feet distance as it is at 1 foot distance, etc.  This is what you are picking up.

The H field radiation from the phone is incidental, it's not used for transmission and there is no "intentional" antenna in the phone to transmit on the H field.  The reason modern phones are more prevalent to this kind of noise (let me guess, it's a Sony-Ericsson phone, right?) is because the Li-ion batteries are a lower voltage, so the whole phone operates on a lower voltage and lower total circuit impedance.  Lower impedance means more current, more current means more H field.

The answer is to either turn the phone off, switch to a different phone that does not use the S-E chipset or design (although my guess is it will get worse with all phones as they progress), or simply put more space between the phone and the susceptible equipment.  My Sony-Ericsson phone will be picked up by anything magnetically sensitive within about a 6 foot distance...  10 feet and it won't pick it up.  Leave the phone in the other room at least 10 feet or more away from your susceptible stuff.

FWIW, this will probably print magnetic tape as well, at least to some degree.  It may build up magnetic flux on the tape heads requiring more frequent degaussing.  IMHO the real answer to your problem is to switch to digital Smile  just kidding.

If I accidentally leave my phone in my pocket during a gig or rehearsal where I'm playing my guitar, it cracks me up because invariably I'll get the delay set up to do near-infinite repeats or something, then the phone will make its noise and get picked up by the guitar pickup, and the delay plays it over and over and over...

See ya-

Offline j.hall

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Re: cell phones in the studio.
« Reply #4 on: May 13, 2004, 11:01:58 am »
WOW.....

that is the answer i'm looking for

help me out a little more if you don't mind

i only get that noise when my phone is actually ringing, it's not constant durring the ringing process

it doesn't happen while placing a call, or durring active concersation.....only while ringing

my phone is most commonly set to vibrate only, sometime ring and vibrate simultaneously....

would i elimante the problem if i just set the phone to silent while working.

i have a nokia

my tracking engineer has whatever sprint uses

is this a shielding issue?

i have static shields on all three decks it's happened on


Offline josh

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Re: cell phones in the studio.
« Reply #5 on: May 13, 2004, 12:11:41 pm »
j.hall wrote on Thu, 13 May 2004 16:01

WOW.....

that is the answer i'm looking for

help me out a little more if you don't mind

i only get that noise when my phone is actually ringing, it's not constant durring the ringing process



You'll get the noise when the phone is about to ring, ringing, or perhaps while it's idle "calling" the tower.  I have never heard a noise like this from my phone while it's operating (talking).  My guess is because the noise is actually caused because of a transitional state that the phone cycles in and out of during ringing and tower comm.

Look at it like this.  As you know, when discharged with no voltage across it, a capacitor is a short circuit.  When a change in voltage across the capacitor occurs, then current flows through the capacitor until it becomes charged, at which point current won't flow any longer.  This is by definition a transient current.  If it's AC, then current will flow the other way when the waveform polarity changes, etc.  But with DC, like the voltage running your cell phone, the cap charges up and then current only flows if it discharges.

The decoupling caps, filter caps and all that on the DC line will do this when you turn a DC circuit from "off" to "on".  So when your cell phone is sitting there doing nothing, the circuitry that's there to ring the phone is "off".  It's in standby, some other state of low-current, or maybe in reset or powered off.  Phones are designed to conserve power.  When it rings, this circuit is turned on, and there is a spike in current flow which is the very definition of what causes an H field to occur, change in state of current flow.  When it goes off, then the capacitors and other things discharge (another current spike, opposite polarity), then if it comes back on, another current spike, etc.  This is what's causing the noise, methinks.  Not for sure, but an educated guess.  If you hear the noise BEFORE the phone rings, this is the cause.  If you hear the noise occasionally when the phone is idle, this is the cause.

The vibrator in the phone is an electromechanical transducer like a speaker (actually it's like a solenoid).  It will DEFINITELY make a cyclic magnetic field.  If you only hear the nosie while it's actually ringing (vibrating), then turning off the vibrator in the phone might alleviate the problem.

Quote:


my phone is most commonly set to vibrate only, sometime ring and vibrate simultaneously....



Try setting it to ring only and see if it helps.  IMHO it might.  If it were a Sony-Ericsson phone, I'd think it wouldn't help.

Quote:


is this a shielding issue?



No.  Shielding does not work on magnetic fields, unless you use a high permeability material like mu metal (very expensive, not likely you can use it).  You could shield the phone with mu metal and it might work, but it would be very hard to use the display, hear a conversation, or push a button Smile.  Maybe you need a mu-metal holster for it Smile

Your shielding is used for other things (notably, it's really used to improve grounding, but I don't want to get back into that debate).


Offline j.hall

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Re: cell phones in the studio.
« Reply #6 on: May 13, 2004, 01:05:25 pm »
awesome man.....

i'll try running the phone in ring only and see what happens with a little blank tape....then put it in silent

pin 1 arguments..............boy that sounds like fun

Offline spankenstein

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Re: cell phones in the studio.
« Reply #7 on: May 13, 2004, 01:39:53 pm »
I just don't see the difference between cell and say radio, or 802.11 wireless or cordless phones. Now the electrical interference could definitely end up on tape if the equipment (amps, guitars, console) pick it up but I am saying that I don't see the cell phone have a direct effect on the tape.

There was a thread on recpit about flying with tape and the X-ray machines. This should be the same.

Offline josh

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Re: cell phones in the studio.
« Reply #8 on: May 13, 2004, 02:48:12 pm »
spankenstein wrote on Thu, 13 May 2004 18:39

I just don't see the difference between cell and say radio, or 802.11 wireless or cordless phones. Now the electrical interference could definitely end up on tape if the equipment (amps, guitars, console) pick it up but I am saying that I don't see the cell phone have a direct effect on the tape.

There was a thread on recpit about flying with tape and the X-ray machines. This should be the same.


Well, neither is it the same, nor should it be the same, but you would have to understand the difference between magnetic fields and electric fields and wave propagation through air and all sorts of other things to really get why.

The phenomenon that j.hall is describing with his cell phone is not related to radiated electric fields such as the signal transmission of a cell phone communication, or of an 802.11 (2.4gHz) Ethernet device or a cell phone (900-5400 MHz depending).  It's related to magnetic field coupling in the near field, which is stimulated by some other effect of the phone other than the direct RF activity of the transceiver.

Put more simply:  THIS IS NOT RADIO INTERFERENCE

It's a magnetic phenomenon that is not related to the radio transmission of the cell phone.

Radio interference does not passively effect magnetic tape because it is not a magnetic field, it is an electric field, and magnetic tape is not susceptible to electric fields by itself.

Now, regarding X-rays...  man you are off the reservation there.  X-rays are 10 BILLION GHz to about 100,000 BILLION GHz.  Most definitely not a magnetic phenomenon.  Even the smallest amount of measurable inductance would render a circuit unresponsive to X-ray-rate radiation.

FWIW, j. hall, in case I didn't make it clear, I doubt this magnetic noise is directly coupling to the actual TAPE or to the tape heads.  Tape heads are pretty well shielded normally (effectively, and by design, by people who understand electromagnetics), and should not be highly susceptible to this noise.  You'd have to have the phone very near to the tape head (sitting on the machine for example) for the HEADS to pick up the noise.  The same is true for magnetic tape.  You can evey operate a degausser within a few meters of a magnetic tape without damaging it, and it has a much higher magnetic field than your cell phone.

No, the reason you hear this "on tape" is because the noise is being picked up by some other susceptible device (a microphone, preamp, mixer channel, guitar amp, guitar pickup, cable, DI box, you name it, they can all pick it up) and you're recording the output of that device onto tape.  I bet if you disconnect all of the inputs of the tape machine and put on a tape, roll it and record it, then induce this noise by calling your cell phone with it in your pocket or a reasonable distance (1 meter or more) from the tape heads, you won't hear a thing on the tape.  Worth a test.  You can always erase it!  

If magnetic media were this wildly susceptible to stray magnetic fields then computer hard disks would be completely non functional in the presence of a CRT monitor!



Offline j.hall

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Re: cell phones in the studio.
« Reply #9 on: May 13, 2004, 03:28:39 pm »
josh, once again, you have answered questions i haven't even asked yet.

thank you SO MUCH, for the help.......i've been really nervous about this.....and now i've got answers.


Offline josh

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Re: cell phones in the studio.
« Reply #10 on: May 13, 2004, 03:54:53 pm »
j.hall wrote on Thu, 13 May 2004 20:28

josh, once again, you have answered questions i haven't even asked yet.

thank you SO MUCH, for the help.......i've been really nervous about this.....and now i've got answers.




Glad I could be of assistance.

Hope this helps.

See ya-

Offline j.hall

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Re: cell phones in the studio.
« Reply #11 on: May 13, 2004, 04:13:40 pm »
oh it helps.....big time

i know what is happening now, and "knowing is half the battle"

hahahahaha

Offline Rivers

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Re: cell phones in the studio.
« Reply #12 on: May 13, 2004, 10:47:28 pm »
This finally became an issue with a session the other day.
The guitarist and I were doing some overdubs and trying to work out a solo and his damn cell kept ringing like every 10 mins.

It just totally destroys the flow/vibe of the session.

I think from now on I am going to either have the bands cut them off or leave them outside the room.
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Offline stickman

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Re: cell phones in the studio.
« Reply #13 on: May 14, 2004, 12:04:55 am »
ok, i cant speak for tape (i just wish i could...)

however, i think something similar happened to me one day. if someone could explain it to me, that'd be great!

so the story goes something like this...

was tracking a vocal to harddisk when my phone rang. i keep recording the singer in the studio while i talk on the phone in the control room. now, i didnt notice it on immediate playback but later on i realise my entire conversation is somehow recorded on the track. low in volume, but its definitely there and clear as day when listened for. every word. clear as day.

is this similar to what you guys are talking about because i didnt know this could happen?

how would this happen? did my voice somehow transmit or intefere with the signal as it went through the console, therefore going onto disk?

or is this common? (i dont get many calls...)

Offline josh

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Re: cell phones in the studio.
« Reply #14 on: May 14, 2004, 11:42:27 am »
stickman wrote on Fri, 14 May 2004 05:04

ok, i cant speak for tape (i just wish i could...)

however, i think something similar happened to me one day. if someone could explain it to me, that'd be great!

so the story goes something like this...


This is not the phenomenon that j. hall was talking about.

Sounds to me like you left the talkback mic on Smile

digital cell phones use encryption and encoding mechanisms that would be impossible to pick up as interference that would be intelligible.  If it was an analog cell phone then it's possible you have a fine-tuned 900 MHz receiver in there somewhere (like the guitarist's cheap wireless rig?).


Offline stickman

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Re: cell phones in the studio.
« Reply #15 on: May 15, 2004, 11:42:35 pm »
 Laughing definitely wasn't the talkback. also, i can hear the other person's voice (on the other end of the line). the whole conversation was there from that sound before the phone rings - you know that pulsy sound you hear in electronics just before it rings - to the end of the conversation.

oh and it wasnt a walkie talkie analogue brick in my hand... honestly, im not making this up!

Offline josh

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Re: cell phones in the studio.
« Reply #16 on: May 17, 2004, 11:24:35 am »
stickman wrote on Sun, 16 May 2004 04:42


oh and it wasnt a walkie talkie analogue brick in my hand... honestly, im not making this up!


Hm.  Maybe you have a dual-mode phone that was in analog mode when the call was made for some reason (insufficient signal from digital network, etc.?)...

Otherwise, that's a big "dunno"...  digital cell phone encryption should make this pretty much impossible.  Even a scanner tuned exactly to the correct frequency will only give you hash/noise from a call made with a digital cell phone.

I think we can rule out RF interference or pickup if in fact the call was a digital cell phone call, simply because this would not be the observed effect.  So either it's an analog call and it could have been (very unlikely, but possible) RF interference, or it's some other phenomenon like magnetic coupling from the speaker magnet to a magnetic pickup nearby...  tape head, guitar pickup, etc., but you'd think the proximity would have to be VERY close and you'd have to turn up the vol on the cell phone speaker VERY high.


Offline imaginarymusic

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Re: cell phones in the studio.
« Reply #17 on: May 17, 2004, 12:12:20 pm »
i think that the reason the noise happens most when the phone is ringing is because the cell tower and phone are "looking" for each other and until a stable connection is established there is a stronger signal.  

Offline stickman

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Re: cell phones in the studio.
« Reply #18 on: May 17, 2004, 10:56:16 pm »
well a couple things just entered my mind which i remember now (it was quite a while ago when this happened).

my initial thoughts were that perhaps there was an equipment malfunction. the console had just been re-wired (not by a professional) in the studio only a couple weeks before.

and, at the time, the phone i had was in a bad state. the aeriel was half hanging out and was sort of only gaffer taped on  Rolling Eyes

also, i remember (and i really dont know why i remember this) that i taking the call with my head right next to a speaker while i was trying to fix something at the console.

now josh, its quite obvious i know nothing about cell technology but could any of these things have accounted for the mishap?

and thanks for all the great info so far...

Offline josh

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Re: cell phones in the studio.
« Reply #19 on: May 18, 2004, 11:12:32 am »
stickman wrote on Tue, 18 May 2004 03:56


now josh, its quite obvious i know nothing about cell technology but could any of these things have accounted for the mishap?

and thanks for all the great info so far...


It may by now be quite obvious that I don't know much about it either Wink

Yes, imho, these all could have had an effect.  Let me do my best Fox Mulder:

1.  If the phone had an antenna, it likely had an analog mode...  if the antenna was nearly broken, it could likely have been resorting to analog mode for the call at hand, in which case, radio interference could have caused the anomaly

2.  Regardless of whether the phone was operating in digital mode or analog mode, close coupling of the handset's speaker to the loudspeaker in the room could have caused magnetic interference, which could have coupled back through the amplifier circuit by some means and made it onto the tape.

3.  Of course the presence of a ground loop or unterminated shield or cable could exacerbate the probability of either #1 or #2.  A ground loop will improve the odds of magnetic coupling, and unterminated shields or interconnects (like a mic cable connected to the board but not connected to a mic) will improve the odds of electric field (radio frequency) coupling.


OK ... so in summary, for indie rock recording engineers, here's the scoop on RF/EM interference:

RF or "radio frequency" interference occurs as a result of electric field transmission.  Electric fields are those whose impedance is greater than 277 ohms, thereby transmiting efficiently over air which has a characteristic impedance of 277 ohms.  Accordingly, electric fields are produced by creating a large voltage into a high impedance antenna (high impedance relative to ground).  Electric fields are therefore picked up by high-impedance antennae, which means wiring etc. that has a high impedance to ground (higher than 277 ohms), such as an electric guitar, any "unbalanced" signal, etc.  Bear in mind outputs on amplifiers are typically low impedance and inputs are high impedance, unless there is a matching transformer or some other terminating device in the amplifier.  Effective shielding can prevent this type of interference.  Electric fields can have high intensity over a long distance.  Cell phones, cordless phones, garage door openers, AM/FM radio, pretty much anything using radio, uses electric fields for transmission.  You can think of this as "capacitive" coupling, and it is caused by voltage.

EM or "electromagnetic" interference occurs as a result of magnetic field coupling, which happens as a result of high-current, low-impedance (less than 277 ohms) circuits which have relatively high inductance.  These fields are received by inductive (magnetic) pickups like guitar pickups, dynamic microphone voice coils, tape heads, or ground loops or other "loop antenna" type sources (that is a conductive loop of material that has some meaningful inductance).  Cell phones and other devices can emit electromagnetic fields, but they have high intensity only very close to the source of the field, and are related to current.  If you have a low-power device that operates at a high voltage (relatively), such as a condenser mic, it is not going to create magnetic fields of any significance.  A high-power device (relatively) operating at a low voltage, such as a CPU in a modern PC, will potentially create large magnetic fields.  Low-frequency energy (such as 60 Hz hum) is generally magnetic, not electric field.  Proximity and grounding improvements are the best way to combat this type of interference.  You can think of this as "inductive" coupling, and it is caused by current.

Specifically for cell phones, digital cell phones operate in the 900-2500 MHz range and intentionally radiate electric fields.  The same is true for modern cordless phones.  Digital cell phones use data encryption and do not, obviously, transmit an analog signal, so if it's an intelligible conversation being picked up, or anything audio (other than just flat out noise), then it's not the electric field from a digital cell phone that's being picked up.  A regular cordless phone may not use encryption and may be analog.  They vary.  Other devices that use analog transmission may be things like FRS radios (which operate in the 49MHz range), CB radio (pretty rare these days), garage door openers (again 49MHz), baby monitors, wireless guitar rigs, and of course broadcast TV and radio.  Suffice to say if you have an electric field pickup problem, you are going to hear TV or radio stations which are present almost everywhere in high intensity long before you are going to pick up a relatively weak cell phone, FRS, cordless phone, etc., signal.

For the most part, RF shielding is a misnomer and not really effective in recording studios, because there simply is not a RF interference problem to begin with...  Audio does not occur at those frequencies, and if you have a device which by happenstance can recieve a modulated signal like FM radio then even the most rudimentary shielding will completely fix it.  60Hz hum is not a RF interference problem nor is it one that can be fixed with shielding.  In fact, to minimize RF and EM field coupling, grounding is the best solution, and circuit layout is #2.

The reason balanced interconnects don't "hum" as much as unbalanced interconnects is because by design, they cancel hum.  They pick up just as much hum.  It has nothing to do with the shielding.  If you ground the "N" wire in a balanced circuit, you will hear the hum, regardless of shield, although it will be less than a 2-conductor unbalanced cable simply because the ground impedance is lower.  The reason "shielded" cables seem to hum less than non-shielded cables is simply because the shield itself is a lower-impedance, lower-inductance ground conductor than a wire would be.  This is simply grounding, not shielding.  In fact, improved shielding would be worse for grounding...  how many of you have noted that "braided" shielded cables are quieter than "foil" shield (which is aluminum foil)?  I can tell you difinitively that foil shield is far and away a better shield than braided shield, but it is not a lower impedance ground conductor.

I could write a book on shielding and grounding for audio, maybe I should.  But I'll quit now and look out if anyone has other questions.


Offline j.hall

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Re: cell phones in the studio.
« Reply #20 on: May 18, 2004, 11:23:08 am »
not to open this can of worms, but if your studio has a proper "audio" ground as a portion of the AC power scheme, and building grounding scheme, you need to lift the shield at one end of each cable, to avoid creating ground loops.

if you don't have the slightest clue what i'm talking about, then you probably don't have an "audio ground" and need to connect the shield all the way through.

for those of us who travel around to different rooms with gear of our own, you need to ask if this has been done.

my protable bays, and snakes are are wired up connecting the shield through out.  

another quick check when i arrive is to see if the console (i do this while hooking up my monitors) has a heavy gauge "green" wire landed on a grounding lug.  i'll also check a few other key pieces of gear for this same thing.  that tells me if the gear is on an isolated ground or not......