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
 

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.

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
 

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.

Sorry ... I was referring to your hardware ... your audio interface

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.

I wanted to see / hear its easy to do. Interesting and good to know. In weird way I'm glad it happens. I like to think of  my music as attempting to model a reality. A little noise in the machine makes it more real for me!

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.
 
 
 
 
 
 
 
 
 
 

Tell you witch one gets me often, is when I am using a TAPE SIM on the master track and forget to turn OFF the emulation tape noise function.... I hear this noise in the background when music is stopped.  I am getting better at it though now (after a few years) that when I hear the noise I check the tape sims first.  :-)
 
Jim

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.

Afrodrum
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.

I can't repro that. I get pure digital silence out of both PC4K Channel and Bus compressors.