Hum from Tram wired lav... some thoughts:

evolvnyc

evolvnyc

Well-known member
I have been using teh exaact same set-up for over 20 interviews, and on the most recent one, I had a killer hum over the audio track, which I for some reason I couldn't hear in the few minutes I had the headphones on (I know, I know, but I'm a one-man-crew). Someone told me yesterday that it is actually better to run a wired lav mic (Tram tr-50) off of phantom power as opposed to using the batteries. I was under the impression that the opposite was true. So here are a few questions:
What is your hum-related experience with the following:
Wired lav mic: phantom vs. battery power?
Shotgun mic: phantom vs. battery power?
DVX plugged into charger vs. runnning on battery?
Wall plug powered Monitors connected via RCA out to dvx: hum?

My setup:
-DVX plugged in to panasonic charger (over 65 hours and no problems!)
-Audiovox 8" widescreen tv as monitor connected via RCA out (video line only, I leave the audio lines unplugged) (powered by wall plug)
-Tram tr-50 wired lav mic into channel one (set to mic) (using batteries for tram: no phantom power)
-AT 897 shotgun mic on stand just out of frame into channel 2 (using AA in AT-897: no phantom power)
 
evolvnyc said:
I have been using teh exaact same set-up for over 20 interviews, and on the most recent one, I had a killer hum over the audio track, which I for some reason I couldn't hear in the few minutes I had the headphones on (I know, I know, but I'm a one-man-crew). Someone told me yesterday that it is actually better to run a wired lav mic (Tram tr-50) off of phantom power as opposed to using the batteries. I was under the impression that the opposite was true. So here are a few questions:
What is your hum-related experience with the following:
Wired lav mic: phantom vs. battery power?
Shotgun mic: phantom vs. battery power?
DVX plugged into charger vs. runnning on battery?
Wall plug powered Monitors connected via RCA out to dvx: hum?

My setup:
-DVX plugged in to panasonic charger (over 65 hours and no problems!)
-Audiovox 8" widescreen tv as monitor connected via RCA out (video line only, I leave the audio lines unplugged) (powered by wall plug)
-Tram tr-50 wired lav mic into channel one (set to mic) (using batteries for tram: no phantom power)
-AT 897 shotgun mic on stand just out of frame into channel 2 (using AA in AT-897: no phantom power)
Click to expand...

Make sure that you weren't crossing the power cables (for lights, monitor, etc) directly over or under the mic cables.

I've never had any problems with phantom power vs. battery on a wired setup.

I usually run my DVX off of batteries, just so that we're not tripping over an extra cable. And I doubt the wall plugged monitor would be an issue, unless again, you're running mic cables over it.

David Kuznicki
Production Manager, WGTE-TV30
 
I'm not trying to be mean

I'm not trying to be mean

I'm going to state the obvious. You know what you need to do to assure yourself of good audio...but you didn't do it. Listen!

I don't care if you are a single person crew. There's no excuse for not listening. Period. Too many pros do the same job all by themselves and they listen. I do to.

Are you trying to do a pro job or is this just a hobby and you don't care if you screw up? I tend to think you want to do a good job all the time.

You could have avoided your hum problem with some simple effort on your part. Now you are stuck with unusable audio and want to look at every other solution except the easiest one that you already know of.

You need to be honest with yourself and do a better job in the future.

Sorry, but all the talk about what you could have done doesn't absolve you of knowing you would have never had the problem in the first place if you'd just plugged in an earpiece or headset.

I'm only being honest with you. Not tryiing to hurt your feelings.
 
You are probably looking at a ground loop hum. It can pop up in any new setup when you have gear externally powered. David's point about the cable getting noise from lying next to a power cable is also a pretty regular issue.

Always, always, always, listen to your headphones.

Good luck
 
no hard feelings lens... the problem, and the issue i'm trying to raise, is that I did check a few times in the phones, and I couldn't even detect it, it was so subtle on the phones, so I'm trying to identify the possible cause, so we can all have a bit more knowledge when we shoot, phones or no.

Can anyone comment on whether it is better to run shotguns/lavs off of battery power in the units or phantom, and why?
 
evolvnyc said:
Can anyone comment on whether it is better to run shotguns/lavs off of battery power in the units or phantom, and why?
Click to expand...

Either way, you use battery juice. The issue then becomes which battery is more reliable. The camera or audio mixer battery, or the smaller, individual battery inside the mic. Both ways work over the short term if you know the batteries are good. But over the long haul, it's how you, as an individual, feel the most confident working, with the ultimate goal of a consistent level of quality in your product.

Part of the answer involves how often you work the gear. Does it sit unused for days on end or are you shooting every day?

If it sits unused...leaving batteries inside equipment can lead to leakage. It takes a while for that to happen but if you are not inclined to actually look at the batteries, prefering to assume without the visual confirmation of it's true condition, then I'd suggest you lean more towards a phantom power setup.

You don't have to have the batteries in the unit and you won't have any unwanted, expensive to repair/replace surprises.

The other reason to use phantom power more often is access to specific battery models. I have a top of the line, but older model, Sony shotgun mic that is as pro as you can get but the battery that fits in it is impossible to find. Because of that, I use the phantom power off my mixer to run it. I don't have a choice.

Phantom power is good for me when I cable lav mics into my cameras for sit down interviews when I'm working alone. I don't have a second person to carry and operate my mixer and I"m not above wanting to save a buck here and there.

My other mics have the batteries in them. They run just as well with or without batteries. Phantom power is not an issue and the batteries are common double As or nine volts. Easy to find but it gets tiring to keep buying, carrying and changing out batteries once or twice a day on a shoot...depending on time used.

There is no single all encompassing answer as to whether to use phantom power. Sometimes it's best. Other times it's not.

A final thought about your original hum problem. In my experience it could be one of several things....and I'm not sure after reading your original post, how involved your setup for the shoot was.

Your battery in the mic could have been low...if it was running on battery...and that can cause hum.

Your mic line was laid across a power cable.

You had a short in your mic cable. A bad connection can be intermittent and a slight movement of a broken cable will give you that nasty noise.

I've had monitors, which were plugged into ungrounded wall plugs, cause a bad hum. It could have also been some other frequency generated by other radios or electrical equipment, like old airconditioners or two way radios.

I only run my cameras, BetaSP or my DVX off of a power supply as a last resort. It's for emergencies only and I do everything I can to not put myself in that situation in the first place. That has also been known to cause a hum...but not very often. If I was a betting person, I'd put money on the problem being poor grounding somewhere in the electrical system.

You don't mention it but...does the problem still exist or did it just happen that time and now the gear works fine?

Audio problems can be frustrating. It always seems so simple until you lose sound, then it's a disaster.

Wear headsets during the entire recording process. If you do it all the time, you'll know when your audio is good or bad, even if the headset or earpiece you use to listen with is not the most advanced/expensive.

Best of luck. We all have had to learn that same lesson the hard way. There was a time when I was young and didn't want to bother with listening. However, I enjoy remaining employed so I had that extra push to change my ways and finally do the job right.:thumbsup:
 
The problem only happened on one interview, and I have done many since with no problems... I agree about wearing the headsets, it is ideal, but sometimes you have to compromise. I'm interviewing people whose entire families have been wiped out (read: murdered) by intentional corporate negligence in a remote corner of the US, and most of them are very sick and elderly, The camera set-up is intimidating enough with the lights and monitors, I feel that when I wear the headphones, they engage me much less, and they are off-put staring at someone with giant senneheiser ear muffs on, which could be understood by them as 'not being listened to.' So yeah, it's a tough call...
Thanks for all the thoughts, Lens. I will do the set-up tonight and see if I can make it happen again.
 
I understand your concerns and they are valid. However...please keep in mind I was promoting just listening to your audio. That doesn't really mean you have to wear a big clunky headset. I use these really cheap earbuds. A single version of what you'd find on a standard MP3 player. I don't hear the total quality of the sound...but I can easily tell if I'm getting any breakup due to cable or wireless problems, even hum.

I'm going to be kind of honest here. If what you're shooting is just a project for you, that you produce, maybe sell, cool. It's your project and you aren't going to fire yourself if you spend time and money (even gas getting to and from the location costs something :laugh: ) only to come back with an unusable, one chance in a lifetime, interview. You've taken all this care to get people to trust you and allow you precious personal access, then, with eyes wide open, choose to gamble on a key element of what you're trying to capture. Sound. Their words from their heart.

Instead of making sure you get that, you're worried about how you look? You've already got lights, a camera, maybe a tripod, how is having a little earbud to listen to going to distract them any more than that?

I know you mentioned YOU would be distracted as well. Keep in mind it's an earbud I'm suggesting. You don't really listen to the interview the whole time with the thing. It's in your ear but you quickly forget it's there because "good" audio is forgettable while you're shooting. Meaning...you get used to paying attention to the earbud audio "just to check" but you quickly hear problems. A crackle or hum is obvious. Problems would be obvious if you checked before the interview and VERY obvious to you if it occurs during the interview. It's like a change of tone that catches your attention because you were used to what it sounded like earlier.

Last thoughts...I promise...let's play this out. You do the interview with this key, grieving family. You get back. No audio..What then? You call them up and say "Hey, can we shoot that interview again?" It seems to me you lose so much having to do that when a simple earbud would save you the time and embarrassment of having to recover from this mistake...which was preventable in the first place.

Thanks for being patient with my thoughts.
 
Hm, right on. Why didn't I think of the earbuds? Perfect! Thanks lens, that's what this forum is all about! :)
 
Thanks for being "cool". Sometimes it's hard to write words and not have people become offended.

You sound very pro. I honestly appreciate your concern for the people you interview.

I have no doubt you will do well.
 
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