More SPDIF

I may have figured out my recording latency problems.  I could try to invent a big story and explanation but here is what's working for me.  There might be some useful generalizations to be drawn.  Whatever, I'm still suffering a little from the New Year's Eve stupidity.

My guitars plug into my Boss GT-10.  The GT-10 plugs (via SPDIF) to my Focusrite Saffire and that, in turn, connects to my computer via Firewire.
The control software for the Saffire has a little button for sample rate which pops up a tiny window:

That little EXT at the bottom locks the Saffire's clock with the digital in (SPDIF).  Seems to be important (and of course, I didn't have it set before).

Additionally, using Audio/MIDI Control (Mac stuff) I selected "Device" for the Clock Source (per an Apple support web page).  And finally I set Ableton to record 24-bit by default (I theorized that this would remove the need to downsample audio its way to the disk).

These new settings allowed me to quarter my sample buffer setting. Previously, I could only set it as low as 256 and often ran at 512 when the tracks started piling up.  Now I can set it between 64 and 128.  This reduces my round trip latency to 11ms in the worst case (down from over 30ms).

Huge.

Clock: A Simple But Very Big Thing

The start of my guitar education marked the start of me using the input half of my snazzy audio interface (Focusrite Saffire). Prior to that my recordings, with a few exceptions, involved "in the box" sounds. Since I started recording myself playing guitar, I've been having timing problems. Sometimes subtle, sometimes not. Being old school, I'd just do a new take. Or being new school, I'd done some more modern magic and make corrections. I have read and heard people talk and complain about latency. I just chalked my problems up to latency and my own n00b guitar chops.

Several people I talked to seemed to think what I was experiencing might be a bit much but until today I've been accepting this crappy state of affairs. What changed? Today, I was playing around with a track from sudara and glu on alonetone. I noodled and noodled but every recording I made was way out of time. wtf!

Eventually, a gasket blew and I recorded myself playing quarter notes with a metronome. The recordings were like a 16th note off! Check the audio settings in Live. The reported inbound latency is 9ms (a lot less than a 16th note!) ... What gives? Look lower. On a Mac, lower in the software stack is CoreAudio and the app you use to configure things is called Audio MIDI Setup (pictured above). Here is where you select the default audio ins and outs, their properties, etc. Looking at my settings, I see Clock Source: and mine was set to Device. I change the setting to Mac and magically my guitar playing no longer sounds like a fall down drunk (just tipsy).

So there it is, I'm a dumbass. But maybe my story will save you some grief. Too bad I won't get back the time I spend recording and discarding takes. Argh!