As you will recall, the usual "IN1/IN2" method for FFT-based OLTF measurement is fine if the IN1/EXC and IN2/EXC coherences are both high. Otherwise, the measurement biases toward 1, regardless of the actual loop shape.

As an illustration of this, I attach a DTT screenshot of one of Haocun's recent dHard pitch OLTF measurements, which apparently shows 1, 3, or 5 UGFs in this loop (depending on what mental coherence cutoff one is using). Next I attach an OLTF plot using the same data as above, but computed using IN1/EXC and converting the CLTF into the OLTF; this avoids the aforementioned bias. Evidently, there is only 1 UGF, and the loop gain below 1 Hz is stronger than what is suggested by DTT.

Since it's very difficult to get high coherence with these ASC loops, it seems like we should not be using IN1/IN2 FFT measurements for loopsmithing. Either we should switch to swept sine (which does demodulate both IN1 and IN2 against the excitation) or we should be exporting the FFT measurements as CLTFs and then plotting the OLTF elsewhere.