Thanks for the question about the pros/cons of wired/wireless mics, I remembered the problem we encountered today with a shoot. Prior to the lecture we tested the sound board and wireless handheld mics. Line into camera from the board was perfectly clear. Speaker arrived and was not comfortable with handheld mic so we switched to a wired lavalier. We had to scrap recording due to the hum in the line. I'm not a sound person but we've got to figure out how to eliminate this. Any thing I can make sure my AV guys troubleshoot? One person in attendance suggested that we may have a bad ground. Any other suggestions will be most helpful. Thanks.
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Jay and Ryanne both offer great solutions. Another solution is lifting the ground- if you are working with professional soundbaords they will likely already have a 3rd prong in this case you can use an adapter to go from 3 to 2 prongs. -if you happen to be going through a DI box there are ground lift switches on them as well (if you are looking for a great DI you will definitely want to go with a PCDI). Brilliant. -there is something called phantom power you mic may require it or may not. if you have it wrong either way this could result in a buzz. On most soundboards this switch is labeled 48v. -check to see if your cables are running parallel with any power cables. This can cause a great deal of hum if your cables are not shielded properly. |
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For all technical troubleshooting, you really have to be like a scientist. Test each part of the process to find the problem. So I would: --use a different cable --if the hum still exists, try a different mic. --if it still exists, try a different sound board. --if it still exists, try using the equipment in a different room to make sure there isnt some local interference. --..... In most cases, it's something simple like a bad cable. |
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as jay mentioned it could be a bad ground, when i've had this issue, i grab another extension cord and re-plug the sound board in, making sure it has that third ground prong on it. |
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I've encountered a rather mysterious hum when shooting with wired lavalier mics that I solved on-site. Later, thinking about it, I decided to reproduce the problem at home and try to determine its cause. I encountered this hum using 2 different camcorders (a Panasonic and a Canon), but in both cases I used wired UNBALANCED mics. These are very common. Mine are Sony electrets that are very high quality, great-sounding omnidirectionals. Plugged into most other recording equipment, I encounter no problems. But into the external mic-in on the camcorders, hum was especially noticeable in quiet moments when the person on-camera stopped talking, and the internal AGC (automatic gain control) boosted the levels. The solution on-site was to run the camcorder from batteries, not the external, plug-in power supply. When home, I tested this out. Indeed, the unbalanced wires from the microphones were allowing hum from the power supply wires to get into the camcorders! Another solution worked as well: a transformer (unbalanced to balanced) at each end of the cable, such that the transformer itself was right up into the camcorder, so no unbalanced cable was available to the power supply wires to pick up any hum. Consistently, removing the external supply and running the camcorder on batteries stopped all the hum. There was no hum when running off of the internal microphones while using the external power supply - only when using external mics. The mic's cables appear to be pretty well shielded, coaxial audio cable. Running them into any other recorder, such as any tape recorder, there is no hum at all and the audio is quite clean. Perhaps in a very long lecture, if one HAD to use the camcorder external power supply, a cleaner supply would correct the problem (such as some filter caps on the DC side). So the first thing to try if this happens to you: if you are running from the external camcorder supply, try running off of camcorder battery! |
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