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Weird hiccups and the search for the cause

Almost as soon as I posted the positive experiences I have with the latest Pro Tools release, our main rig started to act weird under some tasks. It was strange because one problematic session was big, but the other was as tiny as one 5.1 channel and 6 mono channels. The only thing happened in the small session was some editing. I could find a thousand reason why the bigger one made Pro Tools act weird, but honestly this rig usually handles much bigger and much more complicated sessions.

Before anything happens, one warning: Always Save As the session to a new TEST session.

This way you never mess up some valuable real session and anyone can see from the session name that this is NOT a real usable session.

Initiating Sherlock mode

Of course, before shouting that 12.5.2 is bad, it might be wiser to investigate the issues a bit. First of all, let’s see what’s changed lately:

  • Updated Pro Tools to 12.5.2
  • Updated the S6 to the latest 2.2 software
  • Started to use disk cache (28GB)

These alone would be enough, but there are a few more variables here:

  • Both sessions located on our central storage system, so no files on local hard drive
  • One has multiple videos in the session with h264 codec, the second video has been edited to some degree

The errors we received during work:

  • AAE -9129 / Audio processing could not complete due to conflicts with other CPU tasks or a potential clocking issue. If this occurs often, verify your sync cables or try changing the HW Buffer Size…
  • Automation too dense

To be honest, we rarely see any error messages, but receiving multiple ones in 3 days is definitely raises eyebrows.

As many things has changed in the last few days due to the updates I need to test things one by one to be sure that I really find the root of the problem.

Video engine

We use the AJA T-tap on every machine, which is a very nice and dependable little unit, however we all know that the built-in video engine is far from being perfect. To make this worse, as I mentioned before, we use h264 video instead of DnxHD for example. So my first thought was that there’s something going on with this part. First, tried to disable the video engine, then removed all the video from the session but it didn’t make any difference.

The other thing is, the smaller test session didn’t have any video in it to start with, but still as the video engine is always on, I thought this is a good starting point.

After this I turned the video engine on. It is an important step as we never know if multiple things causing trouble.

Central server

Next I tested the connection and availability of our central server. None of the IT and Pro Tools tests showed any problem there. Actually I could double the load on the network and still had ample headroom.

I even asked the IT guys if they modified something in these days, but they didn’t touch anything.

So now we eliminated two things. At this point I started to fear that maybe this new Pro Tools version could be our problem. But never make premature assumptions.

Disk Cache

We’ve never used disk cache before due to the lack of ample RAM for it. I used on some bigger score mixes but only occasionally, always switched it off after the mix. To be honest this was my first thought, but I wanted to be sure.

As soon as I switched it off back to normal all our problems disappeared like if some angel would help us setting up our rig. To be sure that this is the real problem here I made even more tests and sadly it seems that disk cache doesn’t play well with our central server. It’s not a dedicated MAM so this might be a problem.

Worst things happened when the disk cache was on and upon loading the session I wouldn’t wait until the disk cache buffer was completely filled. That way I could produce an error message in any second. If I waited long enough and it was ready, filled up completely, it seemed much more stable but still far less compared to the off state.

Lesson learned

So now we have ample RAM for everything, I switched off disk cache on all machines because they are very stable without it, and quite sensitive and unstable with it. Every workstation is on Yosemite with Pro Tools HD 12.5.2. World peace recovered, after 6 days of testing all seems fine now.