cscott0202 Posted January 25, 2011 Share Posted January 25, 2011 Hi, For all you sound buffs, I really need your help asap!!! I'm back on film location tomorrow! I've have been on location for the past few days recording sound. Marantz solid state recorder hard wired to a Rhode condenser phantom powered on a boom. Professional setup...which WAS giving us exactly what we needed. However today we moved to an old Tudor house for shooting. The problem occurred on playback of the recorded material: We were getting a very frequent buzzing (mobile phone-esque) sound making the audio completely un-usable. It is worth noting we COULD NOT hear this sound while recording...ONLY on playback. With various solutions tried and tested (and obviously all mobile phones off and out of reach), we realised the buildings wireless fire alarm system could be the problem! In fact, we are 99%sure this is the problem. Can anyone suggest a solution? We have tried using foil to deflect signals, new XLR cable etc etc Would really appreciate the help... Link to comment Share on other sites More sharing options...
timd Posted January 25, 2011 Share Posted January 25, 2011 Lateral thinking: Identical length of XLR up the boom following identical route, recorded to second channel on recorder. Subtract the two in the edit. Would that work? Link to comment Share on other sites More sharing options...
cscott0202 Posted January 25, 2011 Author Share Posted January 25, 2011 Cheers fella, If im correct, you're thinking: I need to run a second XLR from the right channel on the recorder. The XLR needs to follow same route up the boom..but do you mean the end of this second XLR has no source on the end (no mic). In other words a redundant cable thats connected to the recorder but may eliminate the interference?? Not entirely sure what you mean here, sorry. Lateral thinking: Identical length of XLR up the boom following identical route, recorded to second channel on recorder. Subtract the two in the edit. Would that work? Link to comment Share on other sites More sharing options...
Simon Lewis Posted January 26, 2011 Share Posted January 26, 2011 Sorry, but I suspect the second XLR cable idea is a non starter. If the source of interference is the wireless fire alarm system, then either the close proximity of the transmitter to the recording equipment is causing breakthrough, or there is a problem on the recording side - the radio signal is "getting in" due to poor EMC design / equipment construction. Usually, effective screening or filtering (ferrite rings etc.) is needed to prevent this, but it can be an involved process. It could even be part of the wireless system that is not working properly. I would certainly check the setup with either a different condensor, or even a dynamic to see if the Rode's mic head amp is susceptible to RFI. Filtering is unlikely to be achievable onsite, (unless you have ferrite torroids in your toolkit?). If it is proximity breakthrough, separation is a good place to start. Link to comment Share on other sites More sharing options...
Andrew C Posted January 26, 2011 Share Posted January 26, 2011 Just a thought. If the interference is there only on playback, are you listening to it in the same location? Are you listening with the devices connected to mains, and recording on battery? You could be hearing the same interference that plagues laptops when connected to earthed sound kit. When you are recording, are you monitoring "off tape" , or before the recording device? Link to comment Share on other sites More sharing options...
Seano Posted January 26, 2011 Share Posted January 26, 2011 Identical length of XLR up the boom following identical route, recorded to second channel on recorder. Subtract the two in the edit. Would that work?It already does work in the mic cable, as well as it can: clicky. Nothing to be gained by adding another unfortunately. Link to comment Share on other sites More sharing options...
timd Posted January 26, 2011 Share Posted January 26, 2011 Didn't think it would work, but worth a try! I suppose if it could work, then the balanced nature of the system would have seen to it already. Link to comment Share on other sites More sharing options...
Shez Posted January 26, 2011 Share Posted January 26, 2011 The logic is moderately sound (sic) actually. A second cable, terminated with the same impedance as the mic will (theoretically) pick up the same interference as the first but none of the wanted audio. So you end up with one channel of sound+interference and one channel of interference. Subtract one from the other and you're left with just the wanted sound. Works fine in theory... ;) Link to comment Share on other sites More sharing options...
mackerr Posted January 26, 2011 Share Posted January 26, 2011 The logic is moderately sound (sic) actually. A second cable, terminated with the same impedance as the mic will (theoretically) pick up the same interference as the first but none of the wanted audio. So you end up with one channel of sound+interference and one channel of interference. Subtract one from the other and you're left with just the wanted sound. Works fine in theory... ;)If the entry point for the interference is the mic (and it often is) the double cable won't work. It only works if the entry point is the cable. A good, balanced, well screened, cable (what should be in a good fishpole) is the least likely entry point. It is most likely the mic itself, or the input of the recorder. If the mic is being monitored with an inline mic pre/headphone amp, and nothing was heard there, it is likely the input to the recorder. Mac Link to comment Share on other sites More sharing options...
ramdram Posted January 26, 2011 Share Posted January 26, 2011 Of interest? http://en.wikipedia.org/wiki/Balanced_line But see the section: Balanced and differential Presume you were filming today? How long did it take before you just switched off the fire alarm? Don't answer that. Link to comment Share on other sites More sharing options...
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