Simple project that makes popping noises - related to plug-in load balancing

Edit: bottom line findings copied from post #11. Link to demo project in post #9
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By rollbacks, I found this noise started happening in the 2016.9 update (22.9), September 2016. The particular feature that stood out was "plug-in load balancing".
 
So I disabled plug-in load balancing (Edit > Preferences > Audio - Playback and Recording, just below the "Use Multiprocessing Engine") and no more pops. As a separate test, with plug-in load balancing enabled, I set my ASIO buffer to 128. No pops. By default, plug-in load balancing only works for buffer sizes 256 and above.
 
Pops for this particular project are associated with the plug-in load balancing feature.
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A project with strange pops.

Start with one stereo audio track, two clips, couple of measures long, separated by a gap of a couple of measures. The clips have short fades at their ends.

The track has the platinum EQ and PC4K S-type chan comp enabled. Settings are default, except the prochannel EQ has 'HP' enabled (40), so the curve points down on the left.

Send this track to a bus with BREVERB 2 in the prochannel, with preset A Cappella Vox. Master bus has concrete limiter. The concrete limiter makes the clicks easier to hear. The Breverb may be an integral part of how the clicks are created, but read on for some contradictory factors.

Project settings: "64-bit Double Precision Engine" disabled. "Always Stream Audio Through FX" enabled.

During playback, the pops are audible ...
1) after the first clip finishes playing and enters the silent measures.
2) after the last clip plays (and the song stops) and also
3) when playback is stopped at any time that audio is not completely silent.
Cases 2 and 3 don't happen when "[] Always Stream Audio Through FX" is unchecked.

With so little in processing elements, I don't think this is related to CPU load, but I have raised the ASIO buffer to 512 anyway. Simultaneous running of LatencyMon shows no problems.

The symptom is not present in Producer X2 or X3. Happens for me on 23.7 and 23.6 (edit: introduced in 22.9).

A weird thing about all this is the clicks/pops can be seen in the track metering. It's easiest to see it when setting the Edit > Preferences > Customization Audio Meter : Rise/Fall time > Peak Fall to 10 ms instead of 1000. Even weirder is that the track meter pulses are eliminated along with the clicks when the bus Breverb is disabled. How could a bus reverb contaminate the track meter?

Deleting the breverb from the bus prochannel and putting the Sonitus delay, Perfectspace, or Blureverb in the bus FX bin causes the same kind of pops.

All of the above is using the 32-bit render engine setting. With 64-bit rendering, these pops don't happen.

After further investigation, I find:
A) No clicks when HP is turned off in the track EQ, or when track EQ, track PC4K, or bus Breverb is disabled. Or when EQ HP Freq is set to above 200 Hz
B) bouncing that single track (source = tracks) to a new track with fast bounce creates a track with a single clip that clicks like the original track. (setting the levels, prochannel, & output bus the same and soloing just the new track of course).
C) with fast bounce disabled, bouncing the original single track to a new track creates a track with a single clip that has visible clicks in the section that should be silent.
D) Like C), but with the original track's output bus to Master instead of the reverb bus. No visible clicks.
***Note: in those bounces, I left Bus FX enabled, but of course Bus FX are not rendered to the new track for source=tracks.
E) Like C), but with Bus FX disabled. No visible clicks.

Hard to be sure, but seemingly the HP option of the prochannel EQ does something to cause these clicks, and the Breverb prochannel, Sonitus FX delay, or similar bus FX is a co-factor. I believe the other prochannel effects in the chain are magnifying the effect.

The difference between B) & C) (fast bounce enabled vs disabled) makes me think there is something wrong with real-time rendering in the 32-bit render engine (not in 64-bits).

These clues indicate some kind of cross-talk with the bus FX into the track:
* the visibility of clicks in the track meter
* the presence of clicks in the source=tracks real-time bounce of C)
 
I previously submitted this along with a demo project to the problem reporter web form, but that whole web interface is gone, so I don't know what will happen to that problem report. Also, I posted this on the Sonar forum. No one picked up on reproducing this. Where is brundlefly?

Thanks for the response, Matt. I've gone ahead and opened a case by email.
 
-- Bill B

Thank you for trying, Alexey. Although the project is "simple", the exact nature may not be so easy to describe. I should post a cwb later. Also, global settings affect the outcome, and could make it hard for others to reproduce.
 
Sample rate 44.1/24. Import bit depth 24. Render bit depth 32. Your question gives me ideas about different settings to try.

Have you tried creating a new project, and importing the audio? I've had it happen once or twice in the past where the project just got corrupted somehow, and the only fix was to import everything into a new project.

-edited for spelling

It's simple, but the behavior depends on just the right settings. So here's a demo project.
Download cwb here. (Google drive seemingly recognizes it as an audio file; don't play it.)

NOT CRAZY (me).
 
By rollbacks, I found this noise started happening in the 2016.9 update (22.9), September 2016. The particular feature that stood out was "plug-in load balancing".
 
So I disabled plug-in load balancing (Edit > Preferences > Audio - Playback and Recording, just below the "Use Multiprocessing Engine") and no more pops. As a separate test, with plug-in load balancing enabled, I set my ASIO buffer to 128. No pops. By default, plug-in load balancing only works for buffer sizes 256 and above.
 
Pops for this particular project are associated with the plug-in load balancing feature.

Thanks for having a deeper look, Matt. Do you find the same behavior on the aux track when the reverb is turned off?

That's definitely an interesting application of an aux track.
 
My other findings suggested 64 bit render engine doesn't cause it and turning off plug-in load balancing also makes it go away. Does the aux track confirm that? (I will get back to my DAW later.)

Hi Matt,
   I tried getting an aux track into the picture. I routed the offending track to an aux track and sent the aux track to the reverb track. With the aux track echo-enabled, the pops are still there. (I'm assuming this is the same routing you used).
 
  But I am unable to record actual spikes onto the aux track. In fact, just having record-enable set on the aux track makes the pops go away while playing through the end of the first clip. When I stop playback or recording, though, pops come back. Of course the spikes can't be captured that way.
 
  As far as those little flat spots recorded onto the aux track, those are very small floating point numbers (as seen by Sound Forge). When setting the render depth as 24 bits, they are just very small integers, nearly 0. I believe the display just shows them at the next pixel away from 0, by convention. Zooming doesn't raise them. Sound Forge is the same way. Where do they come from? Disabling the PC4K S-Type chan comp, flat spots are still there. Disabling the Prochannel EQ or the HP button in the EQ, they are gone.
 
  Replacing the PC4K S-Type with several different prochannel compressors and other effects made the pops go away. Except pops are still there with the PC4k Expander Gate and the PC4K S-type bus compressor. So there's another clue.
 
 Thanks again for your thoughtful and inspiring experiments.
 
   Bill B.

At this point I think we have given Cakewalk enough to think about, and we have gone as far as we can. The crosstalk with the reverb bus is nuts and makes no sense. I think there are some complications with dividing up the work for plug-in load balancing, and something odd about the pc4k family. The reverb and eq are just chance participants (other reverbs do it too).
 
This project is just a simplified example of some kind of special case bug. Originally, this popping happened in a bigger project. I first thought it was Melodyne, since it seemed associated with the ends of some Melodyne clips. It took a process of elimination and then constructing the simple situation from scratch.
 
Thanks for helping, Matt.
 
 
Bill B