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RME User Forum → FireWire & USB series → Question about Latency Fireface vs. PCI-Express
Hi,
I am thinking about using my PC as substitute for a mixing desk. Therefor the question of latency is kind of important.
I have two options:
1. Use an USB-Interface (UFX)
2. Use a PCI-Express-Device (Raydat)
From what I read, the PCI-Express-Devices provide better latency in general - is that true?
Thanks for help and Best Regards,
Tobias
Unless you get really "Fast" AD/DA converters, the UCX is likely to edge out the RayDAT with a "slower" AD/DA converter since it (the UCX) has an extremely low-latency AD/DA section.
Edit - Realized you asked about the UFX (not UCX) - The UFX uses "slower" converters than the UCX, so it will be on par with a PCIe setup with equivalent converters (UFX might have a bit more latency than PCIe if you can't squeak out the UFX's lowest USB Latency settings on your PC). I personally have NEVR owned a Firewire or USB interface - I'm 100% PCI/PCIe from day one, and I've been nothing but thrilled with that format overall.
I don't worry a whole lot about conversion latency as long as it isn't much more than 1ms or so, but it can make a difference.
I've been basically doing what you want to do for over 4-5 years now using RME PCI/PCIe Hardware and all different kinds of AD/AD's (currently using SSL Alphalnks, but have used everything from Multiface/Digiface and ADI-8 Pro's, to Presonus Digimax-LT's and Focusrite Octopre's, and now the SSL's over HDSPe MADI). No mixer in sight - and this system is also used to drive the PA and Headphones for band rehearsal w/o any Latency concerns in the slightest (all "wet through the DAW" with effects and all).
I do run at 32-Samples on the RME Driver 24/7, so some of the PC's real-world horsepower is sacraficed to keep the latency that low - but the Sandy/Ivy Bridge CPU's of today are still very capable performers at these latencies IMO. Overclocking never hurts, either (when done correctly and proven to be stable under all circumstances). Even an older Core-2-Duo (4.3GHz e8600) was able to give me lots of VST processing @ 32-Samples 24/7...
Native ITB Mixing/Tracking/Monitoring is the bees knees for me and my somewhat unconventonal Studio setup. Total Recall of every possible setting is bliss...
Hi Randyman,
I am not sure I we are talking the same subject.
> Unless you get really "Fast" AD/DA converters
What is a fast AD-Converter? My feeling is that its not the converters but the "connection" to the host which slows things down by using buffers for "not-glitching". I did my initiating question because I suspect that with PCIe-Hardware the buffers can be smaller than with USB- or FF Hardware...
> I don't worry a whole lot about conversion latency as long as it isn't much more than 1ms
I am using a Fireface UC with 256 Byte Sample Buffer. Cubase says this is 7ms latency (I think "one-way"). For live-usage I think I need < 5ms "two-way".
BTW: I am going to use one or two ADA8000 AD-Extension... Again: What you mean with "Fast AD-Converter"?
> I do run at 32-Samples on the RME Driver 24/7
This is something I can interpret. As I read you are using PCIe-Cards for this setting?
Thanks and Best Regards,
Tobias
The total system "Round-Trip Analog-to-Analog" latency is a combination of the ASIO Driver's buffering, as well as the AD/DA conversion latency. AD/DA conversion has a latency (it is not instantaneous) - generally around 1ms each way, but it can be much higher and a good deal lower depending on the chips used. The new UCX USB uses super-low-latency AD/DA converters - thus allowing it to end up with a lower overall system latency compared to a PCI/PCIe setup paired with "slower" 1ms AD/DA converters - even if the PCIe card is set to a slightly lower ASIO Buffer! 
As long as you aren't using converters with really high latency (a "Slow" converter), it is not generally much of an issue - but the uber-low-latency ("Fast") converters (like the UCX and ADI8-QS) can be a nice way to get your round-trip latency as low as possible.
I use average speed AD/DA converters (SSL Alphalink: ADC=43 Samples, DAC= 28 Samples), and counter-act it by always running at the 0.75ms (32 Sample) ASIO Buffers in the DAW. But then the resultant CPU Horespower is slightly diminished (the PC has to work harder to get the audio in and out that quick - makes it less efficient overall).
Every single channel of audio in my setup passes through the DAW Software (no direct monitoring or Totalmix used for monitoring) - and system latency is not a concern in the slightest.
As long as your PC will handle your desired DSP Workloads at the lowest ASIO Buffer settings, AND you use only "0-Latency" VST plug-ins in your projects, you are not likely to observe any appreciable "round trip latency". Been doing it this way for almost 5 years now. No mixer in sight! Just be cautious with your VST Plug-ins as some will add thousands of samples of latency!
RME User Forum → FireWire & USB series → Question about Latency Fireface vs. PCI-Express
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