Some of my synths suddenly dramatically lose their tuning. Does anyone have any ideas what could cause this?
 
 
i7-6700 @ 3.40GHz, 16GB RAM - Steinberg UR44 - Novation Impulse 61 - JBL LSR308 Monitors - Sonar Platinum  64 & 32
 
 

Hi. Which synths are you talking about?
All the best.

Errant midi messages would cause it.  they can be coming from anywhere, depending on how you have set up your midi routing, and whether you have hardware controllers that are MISTAKENLY inputting midi data into certain hardware synths.

Make sure your pitch bend wheels or joystick are not causing this by being stuck out of position.

I had this problem once. Turned out to be my usb midi controller was sending errant pitch bend messages.
 
One thing that made it difficult to find the problem was at the time I was unaware that setting midi input to "none" in SONAR is equivalent to "all inputs Omni". If you don't want a track to receive input from midi you should set it to an unused port/channel.

Two synths I've used for the test are Nusofting's Sinnah and De La Mancha's Scylla. I've used these these synths on a number of projects for sometime and the problem has never occurred before. The changes in pitch are very random in nature, so that if I'm playing the keyboard, it happens without warning or reason, and if I'm playing back the recording, it's also random in nature. In other words, there is no consistency in the pattern. UnPredictable and random like something is triggering the synths to dramatically swing off pitch. I can readjust the synth's pitch to bring it back in tune, but the readjustment is not to "0", it is some wild offset of many cents that is only temporary and then the pitch swings over to another aberration. I've not tested everything, but Rapture Pro does not seem to have the problem.  

That describes the problem I had exactly. FWIW the keyboard I had the problem with was a Novation Impulse 49.

OK, I've just tried base 57's Idea. Actually I did set it to "None" and the pitch returned to normal. I'll try the unused channel as well.
 

Base 57, that's what I have. A Novation Impulse 61. That might be it...............................................  Wait, I spoke to soon, there is still a problem. I changed the channel, but there is still a wild pitch swing.
 
Later........I've tested some other synths and many of the other ones I have seem to work, so I'm thinking it might be a problem with the specific synths. Maybe a combination of factors.

IIRC some synths may go out of tune if they are demos.