I record vocals into a Focusrite TwinTrak Pro, which goes into my Tascam FW-1884 firewire desk (32 bit), on SPDIF.
I've just had a crazy latency issue, where the vocals were coming in early. I had to scrap the session!
I fixed it in the end by trashing Logics' prefs.
I believe the trouble lay in the Audio/Devices/Core Audio/Recording Delay preference being set to some random figure. I don't know how...
In the mean time I've been recording Logic's metronome, and comparing the latency (quite small now) on various settings.
One thing I noticed was that the I/O buffer sizes didn't work out as expected - 128 seems about best, 64 was worse, 256 about the same as 128 really. I tested with Low Latency Mode selected, and without, with and without plugins. LLM seems to help a bit, but I couldn't claim my tests were that accurate because of hand holding the headphones to the mike, not getting exactly the same volume every pass.
My whole system is set to 32 bit, for compatibility
with the FW1884.
By the way - is there a quick way of removing all plugins from a session?
So, my question is, how to get the best (lowest) latency? Does the SPDIF add any?