| Hay
About test 2 ,I think you should have a delay as big as your latency settings.
If you want to eliminate it you should give Nuendo/Cubase a way of knowing It is looping by setting this as an External plug-in 1/1/I/O and hitting the little button on the small window it has to represent it.
This will compensate for the delay ,every DAW has this as it takes time for the computer to send sound out.
The test shows latency on your system is PERFECT :-)
And..about the spike changing ,when you send a spike to a D/A converter it overshoots ,there are no perfect spikes in the physical world.
The D/A is doing its best to create an electrical square wave which is not possible.
When this approximation of a square is feeding back to the A/D this is distorted again as the signal you sent got louder then 0DB .It might be louder by 3-6DB..
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