Topic: MIDI Speed PCI/PCIe v. USB
Hello.
I've been an RME user for only a short while - 7-8 months. I own a UFX unit and am very impressed.
I am planning to build myself an ultra low latency (ULLI anyone? MIDI performance station. Now once you realize that MIDI is a very quirky thing, you start looking for a combination of LL performace items; the DAW has to run with the lowest possible buffer so that real time timing errors are minimized and then the speed of the MIDI interface itself has to be as low as possible so that you get an immediate real time feel for your instrument. Of course, that's not all; you have to factor in the speed of the keyboard or whatever triggering device you are using too! So getting a true real time feel for a virtual instrument is no simple thing. It's not like plugging in your fastest audio interface (by RME) and starting recording audio and living happily everafter.
In any case, the faster you can get each individual item in the chain the better off you will be. I've been experimenting with processing my guitar performance in real time in the DAW and I seem to have a cutoff at around 4,5 to 5 ms for when I really start feeling the latency and losing the immediate / intimate feel of the acoustic instrument. The UFX has been serving me great in that department. However, I'm only now beginning with my MIDI performance station build and have only conducted a few MIDI tests with my existing equipment: the UFX and an M-Audio Axiom 61, using Mac OS. I've done some performance tests where I recorded the audio of my keypress and compared that to the appearance of the MIDI note at the DAW, and the appearance of the Audio output at the DAW. I've measured keypress to audio output at 32 samples buffer setting at 96K to be around 7,5ms (10 measurements, max 8.85ms, min 5.78ms, and that’s a jitter range of 3.07ms; oi!). Think about that for a moment. 32 samples of buffer means that once the DAW receives the MIDI input, the audio output will happen in about 2,3ms with the UFX @USB. So the keyboard and the MIDI interface have to account for the 5,2ms.
How can I get a lower overall output latency for MIDI then? Well, I could go PCIe for audio and lower my output latency even further. But there is only about 1 ms of margin in there. The fastest PCIe / converter combos (RME or Lynx) seem to perform at around 1 to 1,3 ms (32 samples 96K). OK. Next step; make the MIDI interface faster and third step get a faster triggering device as well. This is where my question comes in. I am willing to invest in an RME PCI or PCIe solution if that would make the MIDI interface part of this chain faster by at least 1 ms compared to the UFX.
So what gives? Do you have hard and fast numbers for comparing the MIDI interface performance of your PCI/PCIe gear v. your USB gear?
I know the quirks of MIDI don't end there. There is also the problem of the amount of simultaneous MIDI data in transit and that MIDI is a serial interface etc. etc.
Nevertheless, any ballpark figures for how much more juice I could get from PCI/PCIe MIDI compared to USB MIDI?
Thanks!
Derin.