I have 2 desktops running Sonar (1 at a time), running the same up to date Windows 8.1.1, same Sonar X3e and Platinum Ipswich on both, same plugin versions for all 3rd-party effects and synths.
 
1 computer plays back a specific project, with no problems.  The other computer, playing the same project, has random dropouts of sound, but other than the loss of sound there is no discernible evidence of it.  (Meaning there is no taxing of CPU, memory, disk, and all effects are bypassed, and there is no indication in the Performance Module in the control bar, of anything amiss).
 
The 1st computer does have 32 GB of memory, and the problem computer has only 24 GB, but there does not seem to be any indication of the CPU not keeping up, or the memory being taxed, or there being any disk streaming issues.
 
Both computers have solid-state C: drives, another regular SATA III 7,200 rpm drive for Cakewalk Content and Projects, as well as another SATA III 7,200 rpm drive for sample libraries.
 
I just do not know where to look for why this is happening to only that 2nd computer.  (the 1st does have an Intel i7 2600k, while the 2nd computer has an AMD 8350 with 8-cores), but neither CPU is anywhere close to being stressed.
 
Both computers were running the exact same audio interface, with the exact same ASIO driver versions loaded, and the exact same sample rates and ASIO Buffer Sizes, along with matching Sonar Buffer sizes.
 
(Edited to add the following): By the way, I have the ASIO Buffer Size for both computers running at 1024, and the dropouts are occurring during simple playback, with all effects bypassed, and even just soloing on 1 audio track from a single midi track.
 
Anyone have any ideas?
 
Bob Bone
 
 

How about disk I/O buffers? Defragging a HDD becomes almost required maintenance with audio/video work. A dropout from a disk stream would not show the system being taxed, especially with 1024 buffers.

None of the drives show any fragmentation.
 
I DID just run LatencyMon, and it does indicate some issues may be present to cause dropouts, so I am in the process of looking at that.  I should have done so prior to even posting, but I really hadn't thought there would have been any issues - DOH!
 
Bob Bone
 

I would suspect something in the disk access to be causing this but I'm no hardware expert to point you to anything specific.
 
I just noticed similar issues when transferring projects between studio and live DAW and all the sudden the live DAW gave drop-outs despite the project being just a playback of bounced mix stems ... when digging deeper I realized that muted take lanes of alternative mix stems caused this (as these are read from disk because you could unmute anytime during playback). Removing those unused take lanes fixed the issue ... but the SSD must have also been on its way out as it left me for good just a little while after ...

Thanks - I have upped the ASIO Buffer Size to 1024, none of the disks show fragmentation, there is very little CPU demand, Sonar Projects are on a separate drive, Sample Libraries are on a separate drive, and on the C:, there is only Windows, its Recovery Partition, and installed applications.  I altered the Location parameter for all user libraries (Downloads, Desktop, Pictures, Documents, etc.) to be on a different drive, as well, as the C: is a 240 GB SSD drive.
 
And yet, as the project plays along, even with all effects bypassed, it will have gaps in the playback sound, for roughly 1 second at a time, and at various times throughout the playback.  Additionally, I have 1 instance of Kontakt 5 loaded with a factory-supplied Violin Solo patch, and for some reason, in this project, there is a secondary distorted sound being played along with the regular violin sound.  This secondary distorted sound is an octave or so lower than the original violin pitch, but makes the whole sound quite unusable.  I do not know what is causing this to occur either,.
 
I am hoping that someone has faced some or all of the above, and can share some things for me to look at or try.
 
Thanks SOOOOO much, even for just reading through all of this - it is QUITE frustrating.
 
Bob Bone
 

Hi Bob, does this happen with both X3e and Platinum or only one of them?

Regrettably, both X3e and Platinum Ipswich have the same issues
 
Also all of the NI plugins are up to date, too.
 
Bob Bone
 

Hi Bob,
   I am having similar issues so I will be watching with interest. One thing I am looking at is midi playback buffers because it actually says that if they are too low playback may stop unexpectedly. It happens so randomly with me it is going to be hard to figure out.

LatencyMon is a good guide, but another utility I find handy is Moo0 System Monitor (I use the portable version since there is no installation required). It is very rudimentary program which monitors system throughput and will flag chokepoints as they hit. The disk I/O portion of the program can be handy in seeing exactly what your hard drives are doing.

Bob, really odd you should say that because I experienced the EXACT same issue in a project last night that had played perfectly over several times during the past several months, and multiple times in the last week because I was doing a remix. 
 
Interestingly, I had not updated to Ipswich on this computer. So it was running exactly as it had during all the times that the project played properly.
 
However...the computer took a really long time to boot up, like what happens when there's a Windows update. But there was no notification of same...unless it's one of the Win 7 telemetry updates to send back user info. (I would be the most boring person in the world for computer surveillance - "Opened a program called SONAR. Stopped several hours later. Repeated for the next 1,045 days.")
 
I rebooted the computer and the issue went away. It hasn't returned. My current theories involve solar flares, poltergeists, or perhaps a bio-engineered super-race of intelligent poodles who can interfere psychically with computers.
 
I have a neighbor with a poodle. I think it's time to go ask some tough questions.