Calibrating Input Level for Plugins

[MirrorProfiles]

I mean that the maxium input level refers to the highest analog signal level (dBu) the preamp can handle without clipping (in the analog domain) before being converted to digital, that doesn't mean that it will match 0dBFS (digital domain) at that level.

So you need the pream specs + the DAC reference level to exactly calculate the signal level in the digital domain, or measuring the dBFS you get using a reference signal.

One audio interface may have a reference value (analog to digital) of +4 dBu = -18 dBFS and another one may have +4Bu = -20 dBFS. So if I am not terrible mistaken, using the maxium input level of an input is not enough to get a proper calibration.

I’m not really following. All of these specs would provide the information you need.

+4dBu=-18dBFS is the same way as saying 22dBu of headroom, or 0dBFS=22dBu. The highest signal level it can handle before clipping is 0dBFS, and everything scales down from there.

 

[valimaki]

I’m not really following. All of these specs would provide the information you need.

+4dBu=-18dBFS is the same way as saying 22dBu of headroom, or 0dBFS=22dBu. The highest signal level it can handle before clipping is 0dBFS, and everything scales down from there.

Lets say we have two interfaces, both have preams capable of handing a max input level of 14dBu, The first one has a DAC calibration of +4dBu = -18dBFS, the second one uses +4dBu = -20dBFS. Whats the amount of gain needed to reach 0dBFS with a 1Vp signal at minimum preamp gain for each interface?

 

[MirrorProfiles]

Lets say we have two interfaces, both have preams capable of handing a max input level of 14dBu, The first one has a DAC calibration of +4dBu = -18dBFS, the second one uses +4dBu = -20dBFS. Whats the amount of gain needed to reach 0dBFS with a 1Vp signal at minimum preamp gain for each interface?

This is separating the preamp and the A/D which is not really relevant for built in preamps (where its typically not possible to route the preamp anywhere other than straight to the A/D.

The specs for JUST the preamp aren't relative to the converters, thats just analog headroom before they overload. You'll find this on standalone DI boxes and mic preamps but it has nothing to do with calibration for digital levels. All we care about is what digital level a known analog signal is represented as. Mic preamps can add 70-80dB of gain, and output a lot of signal before overloading. Converter specs are designed to accomodate this, so its rare you'll be in a situation where you have a problem unless its a creative choice.

For interface one, the converters can take 22dBu before clipping. Anything before it may well have less headroom and might distort sooner (say like a 9V distortion pedal) - that would be analog clipping though and have no bearing on the dBFS level that hits the DAW.

Interface two has 24dBu=0dBFS. Same thing applies. Typically analog gear will have plenty of headroom before distorting them becomes an issue. And for the average home studio guitarist using an Audient/UAD/Focusrite/etc the specs are provided for the instrument input which includes BOTH the preamp and A/D, so its a solved problem that is all accounted for.