Impedance Measurement timing offset

[trevordj]

I built a ARTA measurement box so I can measure impedance and T/S parameters in REW. I am using the box with an external amplifier and a Steinberg UR22C soundcard. Everything seems to be working well however every time I do my open circuit calibration I get this:

It doesn't seem to depend o the measurement levels or switching the input channels. My measurements look ok. I'm just not sure what is causing this and if there is anything I should do to fix it.

 

[John Mulcahy]

If the results look valid you can ignore it. Some interfaces have timing offsets between their channels, though wouldn't have expected that to include the UR22C. Could try without the amplifier to see if the offset is occurring in the amp somehow.

 

[trevordj]

The results look good and are very consistent so I think I am just going to not worry about it. At some point if I get an opportunity to try another soundcard I will see if that makes a difference. I have a switch wired to remove the attenuation and zener clamp so I will also try and run it off the headphone amp with that switch enabled and see if it goes away.