Yep, same here. There is quite a lot that IK get right and then they seem to shoot themselves in the foot. I’ve tried a LOT to make progress on this and it’s fallen on deaf ears. I suspect they won’t acknowledge this until it’s fixed rather than publicly admitting anything. Which sucks for users but it’s how IK want to do things, and it is what it is.Thanks - I'll try a MM measurement. Wrt Amplitube, that's what I was afraid of as mentioned above: their individual models might be varying wrt to reference input level, and if that's the case and they've lost track, it makes me lose confidence in their level of diligence with respect to accuracy - IK fixing and/or clarifying would be a confidence rebooster to me.
I've always just used USB 5/6 on the Axe FX III as the input into NDSP plugins. I have the signal/noise ratio on my Axe FX so it isn't clipping (10% in my case with active pickups). Is there something else you should be doing in addition to these steps?
If you want the most accurate gain response from the plugins, then yeah, you’ll want to know exactly what headroom this reaches the DAW with. I can try and measure later, essentially it’s a case of running a known voltage sine wave into the DI input at given settings and noting what level it appears in the DAW as. It’s likely that it’ll need some amount of boost or cut to match precisely.