Intermittent hum? at DVinfo.net

Bob Harotunian · November 7th, 2005, 11:23 AM

Just finished a recent wedding taped at a reception facility. I noticed an intermittent electrical sounding hum during some quite ceremony scenes while editing. I was able to minimize most of it with Premiere's Notch filter but was still wondering what could have been the cause.

I use 2 PD-170s and the primary camera had a wireless on the groom. However, both cameras recorded the hum. I assume then that it was an ambient sound. Anyone have an idea where that hum could have originated?
Bob

Don Bloom · November 7th, 2005, 11:01 PM

I had that once this year. Showed up on both my 150s and my JVC5000.
I should have looked up. They had a bunch of ceiling fans running. I had never noticed the hum before with ceiling fans going but I guess this time everything was just right to give the "ghost noise" and give me a headach getting it out of the audio.
Don

Milo Skinner · November 15th, 2005, 03:49 PM

I've experienced the same thing when working as an audio engineer. I've spent many frantic minutes during live gigs trying to chase down induced noise in lav mics - only to realize I was hearing acoustic HVAC noise!

One thought: were your cameras running on batteries or off AC? Anytime you plug into a circuit that also runs lights or any sort of rheostat, you're asking for trouble. I'm guessing you were mobile and on batts, though, eh? If you were plugged in, you might check to see if the hum was worse during lighting changes.

You may also be able to ascertain whether the hum was in the room or in your circuitry by noticing if its characteristics change at all as the orientation of the mic changes throughout the ceremony. Sharp changes in the hum that correlate to mic movement would suggest RF interference. Gradual, smooth changes might identify a room noise being muffled or attenuated by the groom's posture.

I've also had that problem, then realized I had accidentally left the automatic gain control on. In that case, the cam pushed the gain way high when things got quite, and began picking up all sorts of junk. Oops.

Pat Sherman · November 15th, 2005, 04:33 PM

Could the hum be from the input turned up to loud? I know in my case my senn receivers distort if I set the camera to LINE-IN and not mic and the AF-Out to zero or higher. Sennheiser said, never use Line-In always MIC on the camera and turn the AF-OUT down.. Lesson learned there..:) Anyways, it sounded like a hum, but then again everything sounded that way till I sent it to Sony and had it repaired. I had a defective XM-005 audio chip/problem..

Here's a quick test..

Turn on the PD170 and record with the LCd flipped out and then closed.. See if you notice a difference..If you do, you have defective camera..I know it seems odd, I used my PD170 all the time for stuff and never noticed till to moved it into the wedding production side of things and the quiet scenes presented my problem..

November 7th, 2005, 11:23 AM	#1
Bob Harotunian Major Player Join Date: Mar 2003 Location: Somerville, MA Posts: 360	Intermittent hum? Just finished a recent wedding taped at a reception facility. I noticed an intermittent electrical sounding hum during some quite ceremony scenes while editing. I was able to minimize most of it with Premiere's Notch filter but was still wondering what could have been the cause. I use 2 PD-170s and the primary camera had a wireless on the groom. However, both cameras recorded the hum. I assume then that it was an ambient sound. Anyone have an idea where that hum could have originated? Bob

November 7th, 2005, 11:01 PM	#2
Don Bloom Inner Circle Join Date: Jan 2003 Location: Chicago, IL Posts: 6,609	I had that once this year. Showed up on both my 150s and my JVC5000. I should have looked up. They had a bunch of ceiling fans running. I had never noticed the hum before with ceiling fans going but I guess this time everything was just right to give the "ghost noise" and give me a headach getting it out of the audio. Don

November 15th, 2005, 03:49 PM	#3
Milo Skinner New Boot Join Date: Apr 2005 Location: Eugene, Oregon Posts: 14	I've experienced the same thing when working as an audio engineer. I've spent many frantic minutes during live gigs trying to chase down induced noise in lav mics - only to realize I was hearing acoustic HVAC noise! One thought: were your cameras running on batteries or off AC? Anytime you plug into a circuit that also runs lights or any sort of rheostat, you're asking for trouble. I'm guessing you were mobile and on batts, though, eh? If you were plugged in, you might check to see if the hum was worse during lighting changes. You may also be able to ascertain whether the hum was in the room or in your circuitry by noticing if its characteristics change at all as the orientation of the mic changes throughout the ceremony. Sharp changes in the hum that correlate to mic movement would suggest RF interference. Gradual, smooth changes might identify a room noise being muffled or attenuated by the groom's posture. I've also had that problem, then realized I had accidentally left the automatic gain control on. In that case, the cam pushed the gain way high when things got quite, and began picking up all sorts of junk. Oops.

November 15th, 2005, 04:33 PM	#4
Pat Sherman Major Player Join Date: Feb 2005 Location: DuPont, Wa Posts: 325	Could the hum be from the input turned up to loud? I know in my case my senn receivers distort if I set the camera to LINE-IN and not mic and the AF-Out to zero or higher. Sennheiser said, never use Line-In always MIC on the camera and turn the AF-OUT down.. Lesson learned there..:) Anyways, it sounded like a hum, but then again everything sounded that way till I sent it to Sony and had it repaired. I had a defective XM-005 audio chip/problem.. Here's a quick test.. Turn on the PD170 and record with the LCd flipped out and then closed.. See if you notice a difference..If you do, you have defective camera..I know it seems odd, I used my PD170 all the time for stuff and never noticed till to moved it into the wedding production side of things and the quiet scenes presented my problem..