In the OP it's stated that it occurs only on tracks that have program material or previously had program material. The noise was inaudible sitting at -129db. Adding 80db of gain makes it audible. So it's a noise that becomes audible at -40db. In the OP it's something that happens with no effects. You talk about making it audible by adding an amp sim and a distortion pedal.
 
I think you're chasing ghosts. At -129db you must be getting to the limits of your audio interface and seeing artifacts created by its circuitry. Amp sims and OD pedals are real noisy and I can get hum way below -40db by using a high gain amp model. I can be a detail fanatic and have spent days trouble shooting hardware only to find out that test equipment was inserting more noise than the hardware being tested.
 
I would repeat the tests using different spectrum analysers to see if they agree on the findings. If you still get the problem I'd look into getting an AC line supply that was filtered, cleaned and regulated. This thread has me very curious and I'll be following to see how it resolves.

Hi Kylotan,
Yep, I'm getting the same behavior with the PC76 as you. It's weird though, if I drop in another ProChannel module after it in the chain it goes away. For example, if I drop in an instance of Panipulator (or really anything at all except the Quadcurve EQ) after the PC76, even though it's turned on but set to do nothing, it causes that noise to go away. Also, the Pre/Post button seems to cause it to stop, but effects in the FX bin do not.
 
Something funny is going on there, but a work-around might be to just drop in another module that's not doing anything after the PC76 to see if that helps.
 
 
Dean

Razorwit
 a work-around might be to just drop in another module that's not doing anything after the PC76 to see if that helps.
 

Another would be to remove all but the EQ from the PC and set that as track and bus defaults. The OP does not use the PC so I would think this would be the preferred configuration.

ampfixer
In the OP it's stated that it occurs only on tracks that have program material or previously had program material. The noise was inaudible sitting at -129db. Adding 80db of gain makes it audible. So it's a noise that becomes audible at -40db. In the OP it's something that happens with no effects. You talk about making it audible by adding an amp sim and a distortion pedal.

In the OP I hadn't done enough research to be sure of the exact steps to reproduce. Now, I am. See above.
 

I think you're chasing ghosts. At -129db you must be getting to the limits of your audio interface and seeing artifacts created by its circuitry.

 
That's not how digital audio works. A VST doesn't magically get non-zero values passed in from Sonar just because some piece of hardware has limitations. The sound hasn't even hit the hardware yet.
 

I would repeat the tests using different spectrum analysers to see if they agree on the findings.

 
I don't need to. I've heard the hum for myself when the track is amplified, the peak meter in track view is showing that a noise is being generated by Sonar/ProChannel when there is no other effect enabled or input monitoring happening, and Voxengo Span is showing the frequency of that noise clearly. On top of that, several other people have reported similar issues.

scook

Razorwit
 a work-around might be to just drop in another module that's not doing anything after the PC76 to see if that helps.
 

Another would be to remove all but the EQ from the PC and set that as track and bus defaults. The OP does not use the PC so I would think this would be the preferred configuration.

None of this is a problem for me because I'm just going to switch PC off, once I find all the files where the Sonar bug helpfully switched it on for me. I'm just following up because there's another bug or dubious feature here that deserves investigation.

Just did a quick test and yes, PC76 is doing exactly as Kylotan's gif, but with different frequencies (for me, using SPAN, 171-513-etc).
 
And if I add the Tube PC, same thing happens: some frequencies are added, like a ramp, from mid to high.
 
Turning off both, or the ProChannel, clean the analyzer.
 
I can visually see but I can't hear anything.
 
Bug? No bug?
 
¯\_(ツ)_/¯

I was so curious that I picked up span to test my system. I can replicate the OP findings more or less. It is the output from the PC76. If you adjust the output gain or mix of the PC76 the signal in span changes. On my system the noise is at -156db when the PC76 is set normally. (0db gain and 50% mix) If I max the gain and set the mix to 100% I can get the signal up to -130db.
 
After doing all this I still don't see it as a problem because I can't hear it and have to go out of my way to see it. Unless I followed the instructions in this thread I wouldn't know about it. I wish the original equipment had specs this good. 

I too can replicate what the OP sees.
However, the same happens when you use several other effects:
Waves SSL Channel Strip, API-2500, PuigTec EQP1A and every other plug-in with an "Analog", "Noise" or "Mains/Hum" - switch I tested so far will show a peak value on the track, if these switches are on.
The track goes back to complete silence if these "analog" settings are off.
 
Since the 1176 ProChannel module is modeled after analog hardware, the "noise" is probably part of the signal of the emulation.
 
IMHO not a bug, otherwise a lot of plug-ins would be buggy, too.

Klaus
I too can replicate what the OP sees.
However, the same happens when you use several other effects:
Waves SSL Channel Strip, API-2500, PuigTec EQP1A and every other plug-in with an "Analog", "Noise" or "Mains/Hum" - switch I tested so far will show a peak value on the track, if these switches are on.
The track goes back to complete silence if these "analog" settings are off.
 
Since the 1176 ProChannel module is modeled after analog hardware, the "noise" is probably part of the signal of the emulation.
 
IMHO not a bug, otherwise a lot of plug-ins would be buggy, too.

The adc can send small non-zero data to the pc due to inherent circuitry noise. But in the test the audio track does not appear to be set up to receive input from the audio interface. I agree that this is probably modeling noise.

I checked the PC76 at 44.1kHz instead of my usual 48kHz, and the fundamental dropped proportionally from 187 to 172Hz. If it were a deliberate emulation, I would expect the spectrum to be independent of sample rate. I'm not sure why Ben (Kylotan) doesn't see the lower fundamental that I get at 44.1kHz. I see the same spectrum in Span as in SONAR's PC EQ flyout (with sufficient amplification added); it seems like the fundamental he sees is the first harmonic at approx. 3x  the fundamental that I get. Maybe some Span setting is causing it to be missed.