I had settled on ASIO as my driver platform and been quite happy with it for the last couple of years. Tonight, I decided to go through every possible combination of settings in the MOTU applet and Sonar to find the lowest latency with the best stability and here's what I found...
With my test project with lots of tracks and dozens of some of the heaviest FX I have, I tested ASIO, WDM/KS and WASAPI.
In ASIO mode, 128 samples was the low limit with my monster test project. Even though I was not pushing past 40%-50% CPU, dropping to 64 samples would cause glitchy sound. Next, I tried WASAPI, necessitating the "Use WaveRT for Windows Audio" checkbox in the MOTU driver applet to be enabled. Again, my low limit was 128 samples.
Here's where it gets a little interesting. Switching to WDM/KS, again I could only get to 128 samples until I unchecked the "Use WaveRT for Windows Audio" checkbox in the MOTU applet. Once that was off and the card was re-profiled, I found the low limit was down to 64 samples and I could literally throw huge numbers of tracks and plugins at Sonar without so much as a glitch.
For Sonar, the sweet spot for the MOTU applet seems to be 64 samples - then within Sonar, you can have the latency slider all the way to the left and get that 64 sample buffer. If you drop the MOTU applet to 32 samples and re-profile in Sonar, you have to go higher than 64 samples, moving the slider to the right before it's stable, so 64 samples in the MOTU applet is the sweet spot.
In Summary: For best performance in Sonar with MOTU PCIe-424 (or PCIX-424) based gear...
- In the MOTU applet: WaveRT unchecked, 64 samples
- In Sonar: set WDM/KS driver mode & reprofile the card
For the record, I am running a PCIe-424, 2408 Mk3 and a 24I/O on a PC with a 6-core Phenom II with 8 GB of RAM.