I'm hoping to find a solid resolution to this one: Trying to record vocals for a band this past weekend, I was seriously fighting latency vs. drop-outs. This was to the point we simply could not use the Echo abilities in Sonar and reverting back to using MOTU CueMix DSP for low-lantency monitoring (which unfortunately doesn't give us any compression).
 
My setup: Intel Z77 MB, Core i7-3770K, Kingston 16MB DDR3-1600Mhz RAM, Windows7 64, MOTU 24CoreI/O w/OP-AMP mods and BLA clock (I've tried internal clocking as well) (PCIe-424); Sonar X2a-64Bit. Latest version of CueMix DSP, latest drivers for MOTU unit and PCIe card. All updates applied to Windows 7, and no other programs running, no shared drivers. 
 
I set up latency Playback and Record to as low as 64, and froze ALL other tracks except busses (7 of them). With the DAW sitting idle and absolutely no affects on the vocal, I'm still getting about 100ms delay on feedback, which is not fun for the vocalist. I've tried using Record/Play Ahead caching, and have even gon through an exhaustive effort to perfectly synchronize the recorded vocal to the session (even ASIO drivers reported latency is still 30+ samples off). With the latency set to 64 for both, I get drop-outs even with all other tracks frozen.
 
So, with a fast and efficient system, little or no I/O in use, no CPU spikes, low DRAM usage, defragged drive, all plug-ins disabled or removed, I'm still hearing a slight delay from the Echo button in Sonar (up to 100ms). What would be a recommendation anyone has found here that you may have used to better latency that was not covered in the Reference guide? Cakewalk's recommendations got me close, but it's still not useable. Is there anything I can disable in Sonar that might improve this latency?
 
Thanks!

With My MOTU card, I can get a input latency of 2.7msec and an output latency of 3.3msecs roundtrip latency of 6.1 and there is no audible latency heard when recording. If you can get your roundtrip latency to under 12msecs (give or take) then you will not notice any latency.
You MOBO may be an issue also

Keep in mind, this is not using MOTU's own low-latency monitoring, although we had to revert to that. Thanks for the response. I'm curious about the MB, though. This one is quite new.

Do you have any active plugins on any of the buses?

There are some, yes, but not on the buss for Vocals. I tested disabling them anyway, to no avail.

Ah, that was what I was going to suggest trying.  FYI if it was a plugin causing the problem, then it would cause latency for audio I/O no matter which bus it was on (latency compensation is necessarily global). 
 
I had this problem last night, I'd put the TS-64 Transient Shaper on a bass channel and was getting huge latency when I went to play some guitar on different channel.

I do use the Transient-Shaper on the snare from a Send. I also tried for test, disabling the compensation for plug-ins, but that only made things worse when I tried adding a single compressor to the vocal track (which is the main thing to accomplish). As a workaround to this, and the fact that MOTU didn't consider it useful to add FX to the CueMix DSP, we chose to let CueMix DSP return the monitored output to another pair of MOTU outputs where I routed the signal through a compressor, and then back into the headphone amp. It's a terribly old-school way of doing it, but worked like a charm. It's just a bit more work than I'd like to do for one simple task. Still, it may be easier than tackling latency, I'm not sure. hmmmm

Try hitting 'E' on your computer keyboard, for a test.  This toggles off/on the Bypass All Effects.
 
If your project has ANY plugins that are meant for post-tracking (mixing, mastering), then they will affect latency and cause dropouts.  There is a list floating around out there with exactly which plugins to avoid using during recording, but I don't have time to look for it at the moment.
 
Basically, some of the plugins are meant for mixing and mastering, and these can wreak havoc on your tracking.  These types of plugins are either CPU-intensive, or use look-ahead processing, and simply having one or more of these in your project will make things sound really bad if you use them and try to record at the same time.
 
IF you find that bypassing all the effects DOES mitigate the latyency/dropouts, then my suggestion would be to swap out some of these more costly ( processing wise) plugins, for ones that are more intended for use while tracking.
 
Bob Bone
 

Yeah, I forget about keystrokes. They're not always so obvious. I'm going to have more time this evening to mess around with it. 

Have you tried Studio One?