I had a conversation with the Neumann engineer Martin Schneider about the results of our 0-tests and he sent me a list that I have attached to this post.
The list shows how much level difference between the reference signal A and the subtracted signal B causes how much level difference ( leftover) in a 0-test.
Martin sat down and wrote the list and I would like to thank him for allowing me to post it on the forum.
We agreed that the performed 0-test can prove that two signals A and B are identical if there is perfect cancellation or if not they are not identical.
That was Bill's original request. The test showed that an analog mix and a digital mix can not be identical.
As the level differences caused by various inserted circuits are frequency dependent
and in some of the units probably also due to phase shift the matter is complex.
The interpretation is tricky.
However the list shows that even with an ideal phase small level differences between signal A and B lead to big differences in the "underworld" - leftover in our 0-test.
It also shows how good some of the inserted devices like the Haufe transformers really are.
the leftover of the Haufe transformer was -43 dB in my test.
Leaving the aspect of possible phase shift aside and only looking at the level according to the list the level difference caused by the Haufe was at least not greater than 0,06 dB.
A circuit causing a leftover of -32.9 dB in the 0-test caused a level difference of 0,2 dB in real life.
Those units in the test that we love for their sound that caused leftovers of about 18, 19 dB in the "underworld" of the reversed phase-test would have a level difference of about 1dB -1.1 dB according to the list.
Again I made the test with music and of coarse not every frequency was equally represented. The level of the leftovers was always taken at the individual peak, which was dependent on the specific nonlinearity in frequency and dynamic of each circuit.
Another musical material would probably have caused different leftovers.
Regarding the relatively small differences I am amazed that we could hear them by just comparing signal A and B.
What a great tool the ear/brain connection is.
Another interesting result is that even the tiniest differences of 0.0X dB were exactly doubled in the level of the leftover ( +6dB ) when two circuits of the same model were connected in series.
That shows how consistently individual units of the same model show the same character. Ok we used well respected classical brands only.