I have a basic edit system that has developed a problem. A very noticable hum coming from the speakers! I have a mac running FPC that is hooked up to a sony SD camcorder as a dedicated capture deck. I have a big tube television monitor hooked up to the camcorder composite outputs so that I can see what my edits look like on a tv as I edit. I also have the camcorders composite audio outputs running to a home stereo system. When I play my timeline, I can watch on the tv and listen through the stereo system as well as the canvas of the computer monitor. The system has developed a buzz or hum that is generated through the stereo speakers. The sound is similar to that sound you get when you have a bad microphone cable plugged into a P.A. system and it nakes that horrible sound when you wiggle the cable.

So I spent hours going though every cord, wire, connecter in the whole system. I tried everything I could think of to isolate the problem. I have 3 macs so I was able to substitute the computers, I tried another tv, I tried other sony camcorders, I tried unplugging certain appliances. After all of this all I know for sure is this. If the firewire cable connected to the camcorder is unplugged from the camcorder, the buzz stops. Also if I unplug the composite cable from the camcorder the buzz stops. That all I know for sure. I must have missed something somewhere in my troubleshooting.

Again, I tried swapping out computers so the problem does not seem to be related to my computer or the FCP software as I get the buzz even when the computer is OFF. Same thing when the camcorder power is off.

Any help is much appreciated.

That TV is not by chance hooked into your cable system as well is it?

------------------------
Dean

"When I see you floating down the gutter I'll give you a bottle of wine."
Captain Beefheart, Trout Mask Replica.

This sort of problem is amost always caused by something called a "ground loop". It sounds like you're aware of the need to use shielded cables. What happens in a ground loop is that there is a path for 60Hz power to flow along the sheilds on your cables - the shields on the cable actually create the problem they're designed to solve.

The concept is relatively simple, but a bit complicated to explain. Each piece of equipment has what's called a "ground" point. (Many years ago, this "ground" point was expected to be attached the the ground or "earth".) The shield on a cable is connected to this ground point. If you have a more than one shielded cable connected to a piece of equipment, if all the cables don't follow EXACTLY the same path, the "loop" that is formed can pick up electromagnetic interference and transfer it to the equipment input. Also, the power supply cables, especially grounded ones, can help to create a ground loop. And, as has been pointed out above, cable-tv connections are well known for causing these problems. And, yes, the FireWire cable contributes to a ground loop.

There are a number of solutions to these problems. You can get "ground loop" isolation transformers from audio supplies and music stores like Guitar Center. I've found that often, removing the shield connection from all but one of the cables going into the offending piece of equipment often works as a temporary fix - keeping in mind that the shield on each cable does need to be grounded somewhere.

Good luck,

Travis
VoiceOver Guy and Entertainment Technology Enthusiast
[www.VOTalent.com]

Hi Dean,

You solved it! I had Charter Cable hooked into the system in 3 locations. As I disconnected them the ugly buzz went away. By the third coax disconnection, I had sweet silence in my speakers at last.

3 more questions for you, if I may ask.

1.How did you know about this?

2.Why did the problem just surface when the system has been wired that way for a few years.

3. Is there a way to enjoy Cable tv on this system without disconnecting the coax cable every time I want to edit?

THANKS FOR YOUR HELP! You made my night.

I wish I would have posted here before I went through the system wire by wire!

Hi Travis,

Thanks for your info. I guess we were posting at about the same time.

After disconnecting 3 different coax cables from 2 VCR's and the big tube tv, the buzz is completely gone even at high volume levels. No trace at all.

With that problem solved, is there a way to enjoy cable tv on this system without physically disconnecting the coax each time I edit or want to want CNN?

Thanks for your great info!

Frank

I did some online research on "ground loop" and found lots of great info.

I looked for solutions and found this one on ebay. ebay ground loop solution

Any recommendations?

Thanks again!

Frank

Hi Frank,

I've used the device you found, also available here:Markertek.com.

Don't know exactly why your system changed, but your cable TV connection also has a "Reference Ground", which, not only may be thousands of feet from you, but also runs very close to a lot of 60Hz power lines. A cable technician may have simply hooked up or removed a customer, or a neighbor could have plugged in an additional TV, which would have changed your particular ground loop situation.

Travis
VoiceOver Guy and Entertainment Technology Enthusiast
[www.VOTalent.com]

Frank I knew this as I had the same problem. I have never hooked my cable back up to my monitor. I do have a HD monitor hooked up to a $12.00 antennae to watch TV now

------------------------
Dean

"When I see you floating down the gutter I'll give you a bottle of wine."
Captain Beefheart, Trout Mask Replica.