Topic: Latency of Fireface UFX (FF-UFX)
Hello,
I am trying to measure the latency of Fireface UFX (FF-UFX). I want to know if FF-UFX has also an extra latency like in Multiface II (here http://www.rme-audio.de/forum/viewtopic.php?id=12952 is reported that the MF-II produces an extra latency of 15 samples. With the same setup and procedures I am describing below, I also made a measurement with MF II, I can confirm that it occurs an extra latency of 15 samples in MFII…)
The measurement is done with Window 7 PC via USB. The procedures I did are as follow:
- Generate the white noise from MATLAB.
- Route that signal to one output of FF UFX.
- That output is connected to one input of FF UFX with an external cable
- Record the output by compensating ASIO-delay. The ASIO-delay is 1119 samples for a Buffer-Size of 512 samples (sample rate is 48 kHz).
- Compute the latency by performing cross correlation between the generated signal and the recorded signal
The result is that the latency is 0 if DSP EQ+D is ON. However, the latency is -4 if DSP EQ+D is OFF.
Here, I do not understand why setting DSP EQ+D to OFF causes a delay of 4 samples? And why the recorded signal comes earlier, which does not make any sense to me ?
The above result is the outcome of the measurement by a Desktop PC. However, when I tried with an another Desktop-PC and also with a laptop, which have the same OS, the latency is 0 regardless of the DSP EQ+D setting.
So, my questions are:
1)Why the setting DSP EQ+D (OFF, unchecked) causes sometimes (not in all PCs) a delay of about 4 samples?
I know what does the setting DSP EQ+D mean. If you activate this option, the EQ on the signal on the input channels will be recorded with the EQ. If there is no EQ - only the unchanged signal will be recorded. But why this setting (if it is OFF) causes a delay between the generated and the recorded signal?
2) Why is this latency negative? Does it have a special meaning?
3) Does that latency depend on the measurement PC as well???
With the same setup and procedures I described above, I also performed measurements with a Babyface. In this case the measured latency was +1 sample regardless of the DSP EQ+D setting and also in all PCs, I measured with.
4) Why the DSP EQ+D settings does not make any latency difference in the case of Babyface but it does with FF-UFX?
5) How does this ASIO-delay of 1119 samples come about? As I understood from manual:
2*Buffersize =1024 samples
AD/DA =40 samples
Digital-Receiver --> TotalMix --> Transmitter =3 samples
Safety-Buffer =32 samples
1119-(1024+40+3+32)=10 samples
Where do these 10 samples come from? What I am missing? Is there any USB-Bus-delay , which is reported also here http://www.rme-audio.de/forum/viewtopic.php?id=18625?
Best,
Lin