490Hz hum, apparently from inside Sonar (found: ProChannel!)

Okay, here's a strange one. While trying to work out the cause of 1KHz hum being picked up by my guitar, I found out that one of my tracks is also emitting a 490Hz hum (plus harmonics). The weird part is, this happens when playback is stopped, Input Monitoring is off, record is off, there is no input assigned, and the only plugin in the track is the spectrum analyser. It also exists if I turn the FX bin off entirely, although it's inaudible - I just see the peaks appear in Track View, registering at about -129dB. It's not usually noticeable, but (a) it shouldn't be there at all, and (b) when I push 80dB of gain onto the channel via my usual plugins, it becomes audible. The only thing that stops it, is muting the track, or switching off the audio engine.
 
Also - it only seems to happen with certain audio tracks. They are tracks that I have recorded onto in the past, and which have clips in them. But right now they have nothing assigned (as noted above). I've not tried just copying everything into a new track yet, but I'll be doing that if I can't find any other source of this noise.
 
Any suggestions?

Is it still there if you entirely remove the plugins?  I had a similar exerience with a waves plugin called sound shifter a while back. Bypassing didn't help, but it went away once the plugin was removed. Even more bizarrely, the hum did not present in the rendered final, only whilst editing with the plugin loaded onto the track.
 
Could be completely unrelated of course.

Yes, the signal is still there if I remove all the plugins (although I can only tell that from the peak meter - it's too quiet to be audible)
 
However, the culprit DOES appear to be the ProChannel. I never use the ProChannel, and haven't (intentionally) done so this time, either. But when I opened up the strip, and clicked Global On/Off at the top, the noise stopped.
 
I then turned it back on, switched each of the modules off on, and found that the culprit was the compressor at the top. Turning that from 100% wet to 100% dry stopped the tone.
 
I can't reproduce this on any other tracks; but I can switch the tone on or off via the ProChannel for both my affected tracks. Very strange, and not very welcome!
 
Unless there is some sort of vintage compressor that randomly emits a 490Hz hum, I'd say this was a bug. Is anybody else seeing behaviour like this?

I've had that with VB3 also. Still love it though.

Kylotan
Yes, the signal is still there if I remove all the plugins (although I can only tell that from the peak meter - it's too quiet to be audible)
 
However, the culprit DOES appear to be the ProChannel. I never use the ProChannel, and haven't (intentionally) done so this time, either. But when I opened up the strip, and clicked Global On/Off at the top, the noise stopped.
 
I then turned it back on, switched each of the modules off on, and found that the culprit was the compressor at the top. Turning that from 100% wet to 100% dry stopped the tone.
 
I can't reproduce this on any other tracks; but I can switch the tone on or off via the ProChannel for both my affected tracks. Very strange, and not very welcome!
 
Unless there is some sort of vintage compressor that randomly emits a 490Hz hum, I'd say this was a bug. Is anybody else seeing behaviour like this?

Are the preamp gain settings higher on the problem channels?

Kylotan
I don't know what you mean by 'preamp gain' as I don't see any such setting in ProChannel. I do see that ProChannel has defaulted to 'on' in several cases, and that with an input setting of -0.2dB and an output setting of -0.4dB it's not even attempting to be transparent.
 
I went through the project and saw that a whole bunch of tracks actually had the ProChannel enabled, so I went through and switched them all off.
 
This is so annoying because the possibility of having audio-effecting settings in a panel that I never see or view is precisely the reason I don't use or want to use the ProChannel.

If you didn't turn them on, you likely got bit by the automation editing bug that will occasionally, without your knowledge, turn the PC on. The easiest way to spot it is to look at the EQ in the track inspector; if the flat line is grey, no problem, if white, you have a problem.
 
Regards,
Dan
 

Kylotan
That certainly sounds like it could be it. I'm still not sure what essential character a 490Hz hum is supposed to impart but probably somebody knows.

Maybe it's a math thing? Harmonic distortion X silence = 490Hz?
 
Dan
 

I get this relatively frequently too. After a long day of working you start questioning your work and your mix and then suddenly you realize some PC compressor is on. Very annoying.

Kylotan
Unless there is some sort of vintage compressor that randomly emits a 490Hz hum, I'd say this was a bug. Is anybody else seeing behaviour like this?

I can repro getting a -124dB tone from the PC76 compressor when enabled with default settings and no input signal. But I'm seeing the fundamental at around 190Hz (187 to be precise) rather than 490Hz, with harmonics at 3x, 9x, 27x, etc.
 
Doesn't cause me any heartburn in the grand scheme of things, but it's there. I would bet there are many more plugins out there that produce some quiescent noise.
 
 
 
 
 
 
 
 
 
 

It happens to me quite often. Just like dcumpian described, in some strange manner Pro Channel PC4K compressor gets switched on, on several tracks, making awful accumulated noise. Why any instance of PC4K must be noisy ? It is louder than -90dB, I don't remember how much exactly, but makes PC4K useless for me.

Maybe it's amplifying a signal that's interfering with your sound card or cables? My old video card would interfere with my Lynx card, and I've been in studios where cell phone signals, especially when connected to wifi, would interfere with all kinds of equipment, including amps.
 

People who are suggesting that ProChannel plugins might amplify internal noise... that's not how this sort of system works. If you don't have an input assiged to a plugin, absolutely no signal is going in. You could put a whole radio mast next to your PC and nothing will get picked up by the plugin unless an active input is assigned to it.
 
In my case - and a few other people's, it seems - this is noise being generated by the plugin when there is absolutely no other signal going into it. No input assigned, no input monitoring, no playback, nothing.
 
Can I see a reason to generate 490Hz tones (or 187, or whatever)? Maybe, if you're simulating some old hardware that did that. Seems pointless to me but lots of people like that sort of thing. Now I don't know if this is deliberate or a bug, since at least one poster is saying they get silence from their PC compressor.
 
But I think it's a bug, and for this reason - the tone doesn't appear at all, even during playback, until you make an adjustment to the Output level of the compressor, and apparently only you use the FX bin. Try it for yourself - pick an audio track with no ProChannel enabled, enable ProChannel, adjust the Output value a bit, then click the 'Bypass rack' button in the FX bin for that channel, and watch the peak value appear at -120dB or similar. I sometimes find it goes away of its own accord after that; and sometimes it doesn't.
 
Can anyone else repro this? I'm running the latest Manchester update, at 44.1KHz / 24bit recording / 64 bit engine, if that helps.

I attempted to reproduce using your recipe as I understand it and am not able to reproduce the issue you describe on my system.
 
I will, however, keep aware of this and let you know if I see the symptoms you describe.
 
Paul

Does it still happen if you up your latency/buffer size? 

I have no idea which compressor it is, since I don't use the ProChannel at all. It's just a bunch of dials at the top of the strip, there by default.