Hello,
When recording with my Tascam DR-40 audio recorder, I notice it picks up GSM cellphone signals. Sometimes, the signals are so strong as to ruin the recording altogether.
Since that recorder supports "Stereo XLR/TRS mic/line input with phantom power (supports +4 dB line level input)", I was thinking of getting an XLR microphone.
I have a couple of newbie questions:
- Are XLR microphones imune from cellphone interference?
- Are entry level mics good enough for amateur recording? Should I get a self-powered mic or one that will be powered by the recorder through phantom power?
Thank you.
Try StreamFab Downloader and download from Netflix, Amazon, Youtube! Or Try DVDFab and copy Blu-rays!
+ Reply to Thread
Results 1 to 18 of 18
Thread
-
-
afaik it's not even possible for a portable recorder to intercept and record cellphone signals. first the signals are digital and the recorder has no decoder. second gsm frequencies are in the 380MHZ to 1900MHZ range well out of the recorders range of 20-20k htz
--
"a lot of people are better dead" - prisoner KSC2-303 -
What are those, then ?
I get the same issue with my Sony camcorder, although not as bad.
https://vocaroo.com/i/s0jx9tDASq24 -
Have you tested this with your own cellphone to see if a cell phone is truly the origin of the interference?
-
it's in the audible spectrum. maybe a fax machine neary?
[Attachment 47735 - Click to enlarge]--
"a lot of people are better dead" - prisoner KSC2-303 -
Yes, that noise is cell phone signals being picked up by your recording equipment. I get it too -- especially when my smartphone is next to a powered PC speaker. I hear the noise then a second or two later the phone rings.
-
An XLR connection, if properly shielded and wired end-to-end, will cancel out RFI like this. The key is what's called balanced audio.
-
Take a large ferrite ring (those designed for common mode) and pass trough it mic wire few times (wound simple coil), you can also try to use few ferrite beads like this
, ferrite beads or ferrite ring core should be located close to input on your recording devices as possible.
yes but this signal may leak in to devices on all wires also on shielding and as high frequency signal it may be not efficiently attenuated due poor CMRR of most audio inputs (they are signed to deal with sub-MHz mostly power network and LF signals) also parasitic capacitance may be responsible for this... balanced passive (transformer) may behave better but nowadays there is plenty of balanced active (transformer-less) circuits...Last edited by pandy; 5th Jan 2019 at 13:45.
-
Last edited by lingyi; 5th Jan 2019 at 14:40.
-
--
"a lot of people are better dead" - prisoner KSC2-303 -
-
I agree, I don't think it's the phone signal itself since like jagabo's experiences, it always happened seconds before the phone rang / was connected to the network*, so it's something in the phone itself that's causing the interference. It wasn't a steady hum, more like a pulsed on-off rhythmic tone (always the same) that I even got over my car speakers.
*As I recall from my VoiceStream days, cell phones aren't continually connected to towers. Rather they poll during set intervals for the nearest tower even if they're stationary. The old Nokia phones had a secret setting that could extend the polling time (half DTMF?) increasing battery life at the expense of having a longer connect time if moving between towers. I think some Bluetooth devices have this capability also. -
Ahhh...here's an article about it which seems to be limited to GSM phones: https://www.rfvenue.com/blog/2015/05/06/how-to-prevent-cell-phones-from-interfering-wi...udio-equipment
And a sample of the sound I heard: https://www.youtube.com/watch?v=f9nOqTN10Lk
@jagabo - Does this bring back annoying memories? ;-p -
Yes, that's the sound. What I heard was a lot shorter though. That sample had 14 bursts before the continuous buzz. I seem to recall about 3 bursts then the buzz. And the buzz stopped withing a second or so.
It wasn't very loud so it wasn't very annoying. Of course, it would have been if it appeared in audio recordings. -
The interference I heard would vary by where I was. I really think it has to do with the polling of the towers. Just as sometimes it's takes longer than normal to hear the other phone ringing or sometimes you never hear it ring and the other person picks up.
-
Thanks much for the infos.
Before buying an XLR microphone, I'll experiment by just asking everyone within a couple of meters from the microphone to set their phones to plane mode, and see if the issue goes away. -
Using those snap-on ferrite beads will not hurt anything and you will be impressed how "magically" such small thing may improve situation - you can search somewhere in your old cables - perhaps there is somewhere such ferrite.
And explanation is quite simple - strong EM field may induce real current that will trig semiconductor joins to act abnormally (junction work as detection diode and follow power envelope so bursts of energy are easily recognizable) - i saw myself CRT's displays turned OFF by 4W UHF radios, some people reported permanent damage of H deflection switch due of this (and those switches for example BU208 are quite robust as they work in under high voltage and high power so they are not so easy to broke). -
@aedipuss, if EMI/RFI leaks into an analog line, even if the main carrier is highly ultrasonic, there will be what amounts to ring modulation artifacts when that interference signal blends with the "wanted" signal. This includes both sum frequencies and difference frequencies, and it is quite possible that those difference frequencies are in the audible range and can be noticeable, especially with particularly strong phone ring signals.
Add to that the possibility during digital capture of there being enough ultrasonic signal in the resulting analog blend that it "overpowers" the anti-aliasing filters and so alias/foldover signals (birdies) are created in the resulting digital code due to the equivalent of subsampling.
This is unfortunately a common occurrence in location recording, and is something even pros have to watch out for. It even has a name - the "galloping horses" sound.
ScottLast edited by Cornucopia; 6th Jan 2019 at 12:55.
Similar Threads
-
How to boost low level mic signal
By Wheels8 in forum AudioReplies: 8Last Post: 24th May 2017, 12:47 -
Help for begginer - Whats best (recommend) XLR Mic for Canon XF105 cam?
By dean79 in forum Newbie / General discussionsReplies: 2Last Post: 30th Nov 2016, 09:10 -
Mic only picking up high level sounds
By Querorz in forum AudioReplies: 2Last Post: 18th Nov 2016, 12:02 -
Stereo mic - or any external mic work on Kyocera Hydro Elite Android phone?
By brassplyer in forum Camcorders (DV/HDV/AVCHD/HD)Replies: 2Last Post: 17th Nov 2016, 20:08 -
External mic ???
By cd090580 in forum Camcorders (DV/HDV/AVCHD/HD)Replies: 2Last Post: 20th Jul 2015, 13:41