[BScout]

You asked this same question on gearslutz and were given the answer.

dBFs is not the same as dB(C, A, U, etc). VU/analogue meters are not dBFS (which is a digital scale like in Ableton Live.) The XMon meters are analogue. If you want them to measure the same, you need to recalibrate the sources for overhead/dynamic range to match.

So I'd ask you two questions:
A) why does this matter for general sources?
B) do you know how to calibrate outputs? It involves signal at a set frequency and level and a multimeter. Pretty standard work for anyone who has worked with consoles/meters before. Your source needs to have the ability to adjust trim/gain though.

For instance, you can have a source be calibrated to 18 dB (standard for all Avid hardware) or 24 dB (for instance, one option on the SPL Madison). That's a 6dB difference before hitting clipping on the output of the DAC. In this case, clipping is digital before hitting conversion but the actual electrical output is dependent on the manufacturer. And that is the what the meters measure.

But you can align everything if you have the tools. But once again I refer you to (A) question above. As long as it doesn't clip, does it matter for reference material?