Greetings,
I'm working on a project with 15 tracks, a moderate number of efx (mostly EQ and console emulators).  Everything worked fine until I tried to record a new guitar track using TH3.  There is obvious latency when trying to record along to the existing tracks.  I have done all the usual stuff to reduce latency to no avail.  So I tried turning off all efx in the project using the FX button in the Control Bar and it didn't help.  I then re-enabled all efx and started turning off one effect at a time starting at track one.  Track one has an LP64 EQ and a Midnight Compressor 64 in the efx bin.  Nothing changed when I turned off the LP64 or the Midnight compressor individually. But when I turned off both efx by turning off the efx bin, TH3 started working fine.  No more latency from the TH3.  But WHY? 
 
   So what does turning off the track 1 efx bin do that lets TH3 work as expected and how do I make this situation go away?  And, yes, I can record the new guitar track with the track 1 efx bin turned off but it seems like I shouldn't have to do this.  Anybody have any ideas?
 
Thanks,
Bill

I don't know anything about Midnight Compressor. Review the documentation for references to latency, look-ahead buffer or some mention about the plug-in being designed for mixing and master. These are all indications the plug-in requires Plug-in Delay Compensation. The LP 64 EQ is a plug-in designed for mastering and requires a look-ahead buffer. So this plug-in will figure into the PDC calculation.
 
The PDC is used by SONAR to delay the rest of the project in order to keep in sync with the track/bus hosting plug-ins which require buffering.
 
Turning off plug-ins does not force SONAR to recalculate PDC. Toggling the audio engine and bypassing FX bins does.
 
To use the new VST3 LP EQ while tracking set the Precision to Non Linear in the Expert section of the plug-in UI.
 

Thanks a million, scook.  You gave me a very concise answer that explained exactly what was happening.  I will try setting the VST3 LP EQ precision to non linear and see if that does the trick.  Otherwise I'll either replace the LP EQ with another EQ that doesn't require the look ahead buffer or I'll just record the new guitar part with the efx bin turned off.  Your answer made me feel a lot better since I now know WHY the latency was showing up.  I was worried that something had become corrupted in my project (a project that has taken *years* to bring to fruition) and I couldn't have survived that... ;>)
 
Bill