Thanks for the input. Actually I have the sound muted on the computer, I am using headphones to monitor the sound and the camera mic is not being used at all. I'm running three ambient mics and one wireless through a small mixer board, then the output from the mixer directly into the line input into the camera.

During testing I actually muted all mics when hearing the noise and it makes no difference, therefore I'm pretty sure it's simply the computer is generating the noise throught the dv cable and I'm not sure if I can suppress that at all.

I think your assumption is right. Electrical noise from the laptop is making its way up the firewire cable, through the camera and into the mixer. Check if this still happens if you run the laptop off its batteries. One of the most likely souces of the noise is the power supply.
Even if that doesn't cure it try this. Get one of those ferrite bead things and wind a few turns of the firewire cable throught that. Some of the good firewire cables come with them already fitted but that might not provide enough filtering.

You could also try adding transformers into the audio from the mixer.
The other problem that's possibly not helping is cameras have AGC on the audio line inputs. This is not so good by itself but if the level out of the desk is low then the AGC will turn the gain up in the camera making the noise even worse.

Bob.

Bob.

Follow Bob's suggestion about trying battery power. I use a noise-busting power strip (Tripplite) on my laptop wherever I go.

If that doesn't cure it, know that all firewire cables are not created equal. The one that came with my first camcorder was skinny and had all kinds of problems. Generally the thicker the better. Plan on spending between $30-$40 for a good rugged one.

Although, it may be camera motor emi getting into the computer rather than the other way around. Hard drive emi is not constant, but variable in pitch and duration.

This is a long shot suggestion, expecially since it sounds like you've been thorough in tracing the noise. I encountered a laptop recently that put a high pitched noise into the headphone out circuit (not your problem) when the CD drive was spinning. Make sure someone didn't leave a CD in the drive. (again, I suspect you would have noticed this).

During testing I actually muted all mics when hearing the noise and it makes no difference, therefore I'm pretty sure it's simply the computer is generating the noise throught the dv cable and I'm not sure if I can suppress that at all.

You may be right but, I don't see how that's a logical assumption. I would have thought that the next step would be to remove the mixer from the chain.

After testing all possibilities, the noise was definitely coming from the laptop. I tried my desktop and no noise, but it's a little too cumbersome to take to the traingin.

Have you tried running the laptop from its battery?
If that stops the noise then it's laptop power supply that is the source of the noise. You could simply run the laptop form a big external battery or an alternate power supply.

As I mentioned above you may also get some joy fitting a ferrite toroid to the firewire cable.

Bob.

Hmmmmm, I guess I hadn't tried removing the a/c charger pwr supply, even though it was mentioned earlier. Just did another test, and yes, it's as quite as in outer space, "Where no one can hear you scream" from my fav movie.

Guess I just needed that one last push Bob, thanks.

Now I just need to figure out a pwr supply, the battery is no good, last's about 20 mins. I'll get this one covered, just got to make sure I wire the plug correctly, not my laptop!

Don

Hope you have a different series HP than I have. Mine uses a power supply that outputs AC. The AC/DC conversion is done internally by the laptop. Check the power supply labeling to see if the output is AC or DC.

Most things that feed AC from a transformer into them will very happily run off DC and the good news is generally the polarity doesn't matter if they use a full wave rectifier. If its being supplied 12VAC then it'll also run off 12VDC.

There's a number of aftermaket external large laptop batteries available that come with every plug you're likely to need.

The problem however might be solved much more easily. I'd start by trying to stop the RFI getting from the laptop into the camera and as the firewire cable is the only connection between the two the good old ferrite bead / toroid could save the day. I've got a couple kicking around the office but the cost of postage would kill the free offer. They are very cheap, easily obtained and easy to fit. You might even be able to score a new firewire cable with one built in, pretty certain the Sony cables have them. Look for a firewire cable with a lump at one end of the cable. Alternatively most electronics shops will stock ones you can simply clamp over the cable, it might help to have the cable loop through the ferrite for a couple of turns.

Bob.

Did you try a simple ground lift on the laptop adaptor. It completly saved me on a multimedia event lastly...

QUOTE: Did you try a simple ground lift on the laptop adaptor. It completly saved me on a multimedia event lastly...


Yes, yes, yes. you beat me to the suggestion. I have an HP/Compaq laptop that does the exact same thing with a USB audio interface. Installed a ground lift adapter on the AC plug and bingo - problem gone. There is apparently a ground loop between the laptop and (in my case) the mixer plugged into the same power strip. Sounds like your situation is similar with the laptop/AC/mixer/camera/firewire to laptop ground loop.

I bet the noise is coming from the switching power supply (they are notorious for generating noise) and is traveling back through the ground into the mixer.

Tom

Thanks to everyone for the input. As of last night I had made up my mind the only thing to do was to get a 12v & a 6v car battery and put them in series on hook it up to the laptop. This morning I'm like, "ya this isn't practical".

So I hooked everything back up before I checked back into the forum, unplugged the camera powerpack, no help, still noise. Then it came to me, what about a ground isolator, since the laptop powerpack is a three prong.

I unplugged the laptop, noise went away, put the ground adaptor on and plugged it back in and no noise. I checked the laptop and infact it show the powerpack was running the laptop. Wow, I really couldn't believe it was so simple.

The laptop I was borrowing was needed back by the owner, so I borrowed a different one and it had the exact same problem, and yes, the ground adaptor also fixed the issue, "YES".