High frequency noise on IO192 outputs

[jiggy_bau]

I have a HD3 system based on a G5 Mac, and two IO192 interfaces. A long time ago, I've noticed that there's an extremly high level of noise on my mixing console, and I was supprised to find out that the noise is actually coming from my Pro Tools system. The noise is completely inaudible, but nevertheless it's there - the meters are reading a rather high level on the master bus. Today I even did a test: I disconnected all the other equipment around the IO192 interfaces, and I've disconnected all the inputs coming to the interfaces - but the noise was still there. Then I tried applying low-pass filter (starting at around 5kHz) on my console, and sure enough, the noise dissapeared. What's interesting is that the noise doesn't start until I start the Pro Tools software (it starts at the point when the interfaces start producing those clicking sounds). By the way, I have a Pro Tools 6.9.1cs3 and Mac OS 10.3.9. I don't have the G5 specs here, but I'll post them tommorow.
In the meantime, I've read this article about G5 power supply problem (http://www.soundonsound.com/sos/may0...applenotes.htm) and wondered if this might be the problem. Another possibility is that the clock signal is somehow spilling into the audio leads. It's definitely not a problem with ground loops or poor-quality power supply, beacuse the studio uses balanced connnections and everything is powered from the same source.
All ideas are welcome...

[Andre Knecht]

Is this noise present only while a session is open? If so, it could be dithering noise, if you have such a plug-in inline on the outputs you’re observing on your meters.

IHTH.

[jiggy_bau]

The noise starts as soon as the IO192 interfaces are activated (at some point during Pro Tools startup they start clicking) and it persists even after I quit Pro Tools (obviousy, the interfaces remain active after quiting Pro Tools). The noise has nothing to do with dithering plug-ins or any other plug-ins, since it's there even when I start a new session with no tracks and no inserts.

In the meantime I checked the compatibility page on digidesign.com, and it does say that PT 6.9.1 requires Mac OS 10.3.8 and that it hasn't been tested with 10.3.9. Now, I could downgrade to 10.3.8, but that means reinstalling the whole system (as far as I know...), which I wouldn't mind doing if I was 100% certain that it would solve the problem.

Does anyone out there use 6.9.1 on 10.3.9?

[Impala]

It's definitely not a problem with ground loops or poor-quality power supply, beacuse the studio uses balanced connnections and everything is powered from the same source.

Though you stated as above, I'm experiencing a similar hi-freq noise problem when I run the air conditioner. All stuff is fed from UPS and the building has it's separate ground line but I called the electric guy and he told sth like "it might be because of the grounding is getting old (oxidation)" and he's going to replace the stick burried in ground.

May or may not be your case but I wanted to note.

Good luck

[audiogeek1]

On our Euphonix CS 2000 we see the noise all the time. Pro Tools does not need to be active. The converters default to 48k because of house sync. When we open PT and change sampling rates it lessens the meter @96k and at 192K it goes too far up for our meters to read. This noise is in audible but it meters. It only happens on one of our CS 2000 consoles and does not do it on our System 5.

Kind of wierd but does not seem to effect what we are hearing. Been like this since we got the 192s a few years ago.

Mike

[jiggy_bau]

Mike, you won't believe this, but we also have Euphonix CS2000! I don't know what this means, but it could be that this noise is always present, but not many consoles are capable of measuring it.

I must try changing the sampling rate as you described, and see what happens with the noise. It makes sense, though, that the noise will go higher and higher in the frequency range, up to a point when meters will stop reading it...

Now, I really don't mind having inaudible noise present in my signal, but I'm afraid that my tweeters might. If this hi-freq noise is constantly feeding the tweeters, they might eventualy burn!

[audiogeek1]

Well we haven't had any problems with our tweeters. The Genelec S30s that we use go to about 35khz. We have not measured anything comming out of them. I think it is up there higher than that. Most tweeters I know of cannot produce signal that High. Unless you have the Super Tweeter.

Mike

[audiogeek1]

Also we are on a PC with an HD4. So the operating system has nothing to do with it. We noticed it in version 6.2.3 all the way to 7.1. But it does not seem to be software dependant. It happens when they are on.

This was the same for us on the 888/24. We got rid of them and went with the Euphonix 727/703/713 converters and had 0 noise.

Mike

[jiggy_bau]

Mike,
Are you saying that Euphonix converters can work with Pro Tools? Or have you simply used the digital outs on IO192 to transfer audio to Euphonix converters?

Paul

[jiggy_bau]

Digi, how about a comment on this subject? At least say you're aware of the problem... This is a serious malfunction - if it indeed is a problem with IO192. I have a bunch of converters in my studio (e.g. RME ADI 8 DS) and none of them exhibits such behaviour. Please drop a line and at least assure me that I shouldn't worry about this noise (my main concern are the tweeters)...