Interesting XP and Firewire Information

Some of you may have read my recent saga of USB 1.1 vs USB 2.0, and then my decision to chuck USB and go Firewire on my Dell Lattitude 830B laptop running XP SP3. I got a Focusrite Saffire Pro 14 interface, and my latencies did improve somewhat, but nowhere near what I had hoped.

SO- I dug even deeper into the available internet info on tweeking XP for audio, and found out something very important. Apparently, if you upgraded to XP to SP2, then to SP3 (as I had), there was a minor problem with the patches that causes the Firewire ports to revert to S100 mode even if they are capable of S400 or S800 speeds. Info from Microsoft is here:

http://support.microsoft.com/kb/885222

http://support.microsoft.com/kb/955408

I checked my system, and, sure enough, the port was not enabled for S400 operation. I made the registry changes as described in the first link, and my latencies were instantly cut in half. It's like playing on a whole new system.

Oddly enough (to me, there is probably a sound technical reason for it), my buffer sizes are the same. However, the round trip latencies being reported by Cakewalk Producer are about half of what they were, and it is much easier to hit and hold a groove while recording.

It took me a lot of time to figure this out, and I wanted to share it here in hopes that I might help one of my brothers or sisters here out. And I thank everyone who responded to my other thread with information.

You know, that's a good point. I didn't notice that. The spec sheet on my Dell says only that it's a 1394 high speed interface, so I'm not sure if it's spec'd to the a or b sepcification.
 
I do know it made HUGE difference (very obvious and unmistakeable) when I made the change.

msr


Maybe this an obvious question, but how do you tell to what speed the port has been enabled?

Well, when I looked for the SidSpeed variable in the Registry as described in the first article I linked, it wasn't there, which, if I understood the article correctly,  means that the port is defaulted to S100 mode. I put in the new key as the article described, set it for the S400 value (2), and everything got a lot faster.
 
I am not an IT professional or anything, just a long time end user. Make sure, if you try this, you back up your registry first so you can get back if things go wrong, and follow the instructions exactly. The instructions are correct, at least they worked for me.

 I put in the new key as the article described, set it for the S400 value (2), and everything got a lot faster.  

rrsis


 I put in the new key as the article described, set it for the S400 value (2), and everything got a lot faster.  

Cool! I was pretty amazed myself. Glad it worked for you.

I did find that I had no registry entries for this either, so I assume I am at S100.  Do any of you know if I use a registry data value of (3) if I don't have S800 capability, will it revert back to S100?  Or, if in doubt, should I just use a value of (2) for S400?

msr