Scenario1: audio track without plugins, routed externally through DA/AD conversion and a loopback cable. send one-sample spike and record it back to another channel. nudge back X samples to align to the original.
Scenario2: audio track with plugin, routed externally through DA/AD conversion and a loopback cable. send one-sample spike (through the plugin) and record it back to another channel. nudge back Y samples to align to the original.
This is how it has always been done. Then calculate Y-X to see how many samples the plugin needs for processing. Nowadays the plugin reports the needed delay and there is ADC to help us compensate. But just to be sure, it can be verified: repeat steps one and two and do the math; surprisingly, the result matches to whatever the plugin reports.
Now repeat this same procedure when using RTAS native processing, and not only does the native buffer repsesent itself, but depending on the plugin there might also be additional plugin processing latency (lookahead dynamics processing, anyone).
I don't see it in that window (for reference, the window is shown on page 795 of the latest reference guide). It just doesn't seem to be there, where do you see it in that window?
I don't have a page 795 on my Protools HD 7.2 reference guide. I'm so sorry, but this time I confess that I'm too lazy to download a 7.3 guide as printed manual is so much easier to my eyes. What I mean is the Setup/Session window that can be opened with Apple-two key combination. It shows total system delay, which *can* be trusted.
For example, my current fairly large mixer reports 188 samples, which @96kHz means almost 2ms. That's a lot, but there's a lot going on in my mixer as well. But just for demonstration -- when I close that session and open a fresh one, the session setup window reports zero samples total system delay. The number grows step by step when I build my mixer.
To give you a basic real-world example; I feed one audio stream through AD and DA conversion and the session setup window reports 29 samples total delay. That is 14 samples for AD conversion, 1 sample for connecting to TDM mixer (because I use dithered mixer so there's processing involved) and 14 samples for DA conversion. Feed another stream and the window still reports 29 samples as the two naturally happen simultaneously. Insert a ReVibe reverb to the track, the plugin reports 2 samples delay and the session window now reports 31 samples total delay. Insert another ReVibe reverb to the same track, the session window reports 33 samples total delay. It all makes perfect sense and the latency does grow with whatever you build to the mixer.
So, as all systems have AD and DA conversion, those can be omitted. If we did so, let's say this basic example goes like this:
1) fresh start, zero delay
2) one stream, one sample delay
3) two streams, one sample delay
4) two streams plus one reverb (on track one), three samples delay
5) two streams plus two reverbs (both on track one), five samples delay
Need I say more?
