Why 18?

[SouthSIDE Glen]

You've kind of touched on this, but after reading the thread to this point I think your reference should be the voltage level at +4. Line up all the various standards to that.

But does it really matter which standard you choose as your "base" standard? What's important here is how they line up relative to each other.

What the question really is when asking what is the "reference", is what is the measurement scale - that is, on a vertical bar chart, what is the Y axis unit of measurement?

In this case there really is only one way to answer that that makes any sense to the subject, and that's to use dBu as the scale. And with dBu, technically the reference value is really 0dBu, defined as .775v. But yeah, if the charts are lined up to 0dBu, they'll be lined up to +4dBu as well (and to any other dBu value, FTM; that's the whole point! ) Obviously +4dBu is the key value here, and not to worry; it is prominant on the chart. (Less prominent, but still noted are the 0dBu reference, and a line at -7.8dBu to represent the -10dBv level.)

As far as which "standard" do I start with? No it really doesn't matter much, you're right, since it will be user-selectable anyway. But I do have to start out with a default starting point, and I at least had to know what I was talking about when explaining that starting point, hence the need to know about the various standards, and hence the need for this thread.

It seems to me that an increasing amount of gear is migrating to more headroom and actually going with the +4dBu = -20dBFS calibration (which makes sense to me). But I think I'm going to default the chart to -18 to actually use the "conventional wisdom" as the starting point, and then letting the user select the actual reality values for themselves from there.

G.