High pitch whine or noise when recording

[Isabelle]

I work on a MAC OSX with Pro-Tools 6.1, the 888/24, USD, and a firewire external disk from which I import my movies. I record foley, so I have one mic input assigned to all my tracks and work with the show's guidetrack. My problem is, I have a high pitch whine that bleeds on my "record" track and modulates in real time with the signal of the other tracks. The louder their signal, the louder the noise. Putting my tracks on mute reduces 95% of the noise but renders my guidetrack unusable while recording, which is not practical or efficient. None of the techs here have any idea where this noise comes from.

Thank you for any information you can offer

Isabelle Larin

[Noiz2]

sounds like a feedback loop. Make sure you are not inadvertantly feeding and output.aux,sendetc back into an input either inthe PT mixer or outboard.

[dunebuggy]

Check if the sync(ntsc or Pal)in your USD is in good condition

[frenchman]

Just a thought, this may also have something to do with grounding : it may require to re-evaluate the whole grounding chain
Computers and audio don't always get along very well in this respect and a bad earth can really be a problem.
Check also problems associated with balanced and unbalanced cables.
hope this helps
good luck

[Doug Ring]

Can you give us more information, please, Isabelle?

Is this noise coming from the mic itself? Can you hear it if you plug the mic into a mixer or voice channel and listen to its output? Does it just appear when you put Pro Tools into record? Try switching to input monitoring on PT so that you can eliminate the effects of record switching. What if you route it to just one PT track? Have you changed your system in any way recently, such as adding other components?

I agree with Frenchman that there may be an earthing issue. This could have built up over time as dirt and corrosion have affected the connections. It might be worth getting some switch cleaner and going through your connectors one by one unplugging them, giving them a spray and re-connecting them.

[deafguy]

Check your word clock. Your session may be at a different rate.

[David Schober]

I agree with the grouding suspicions. Interesting that you have your mic assigned to all inputs....could be some sort of feedback loop.

The question I'd start with is how you're getting the mic to the 888, and then your monitoring system. Disconnect everything from the PT rig (input and output connectors, word clock and SMPTE connections, if any) and record something, anything. (no not the Todd Rundgren album!) to say 8 different tracks. Go straight out of a mic pre without any monitor or mixing console hooked up. Then disconnect the mic pre and reconnect the outputs to your monitoring system. Then listen to see if the problem is still there. If it's gone your problem has to do with getting the signal in. If not, it's a playback issue.

This is only way to check things out, but maybe you get the idea of the process I'd use. I'd also eliminate the USD when doing the test. Don't just turn it off. Physically disconnect it from everything Go from a totally stripped down system and get one thing working at a time. Then add back what you need, one at a time so you can find the issue.

[Isabelle]

I have talked with our head technician here about the various suggestions and the grounding issue is definitely one he will look into. He is interrested to know what your grounding protocol is, to compare it with his own (particularly for my patchbay).

I've been working on Pro Tools since August. I was previously on a completely different system and had many problems but not this one. We did troublshoot the analog part of the signal path -mic, pre-amp, compressor, console, etc. -and all was clean. The noise does not sound analog at all, it is definitely digital.

The noise is directly related to the signal from other tracks. Let's say that on my guide track I have a character speaking, then laughing out loud; when I press play/record, the noise will come in when he starts speaking, get louder when he laughs and then die when he stops laughing. Any track with significant signal will contaminate my "record" track. Putting them on mute let's me record clean takes, but is not a practical solution.

I will try switching to input monitoring and assigning to only one track as a test, but I couldn't work in this configuration because the nature of my job requires me to punch inside existing clips (I have to hear playback) and change tracks all the time (I do about 500 punches a day on 8 tracks).

Your suggestions (and others as well) are very helpful, thank you

Isabelle

[David Schober]

Hi Isabelle,

So it sounds like you're playing back PT into a console of some sort. Have you tried a test of muting at the console (by the way, analog or digital console?) instead of muting the PT tracks? Where I'm going with this is to see where the issue is occuring. That's why I said try doing the recording process that normally causes you trouble, but do it with the PT outputs and inputs disconnected. If it still happens you have some sort of wierd PT issue. If it's clean, then the issue happens outside the box.

Another idea...try recording on to a different hard drive.

As for grounding, I'd say ground everything and listen for hum. Lift items one by one until you find it. But the grounding problems I'm referring to are possible internal grounding problems in a hardware device like the 888 or your Mac, or USD, or maybe your I/O cables.

Did you try taking out the USD?

Strip the system all the way down until it's clean...then rebuild.

One last thing...but I don't think it is your problem. Whenever I get wierndness I will often reseat all of the Digi cards in the computer. (trying to appease the digital gods sometimes works)

Good luck

[Isabelle]

Hi David,

I have an analog console and muting my tracks there doesn't change anything. I see the logic in your methodology and we did do some troubleshooting within the Pro Tools environment but not to the extent that you are suggesting. We will be checking out all of your suggestions as soon as we can and maybe I'll throw in an incantation to those digital Gods, just in case.

Thank you

Isabelle