Best way to measure total I/o latency?

[Ru_C]

Hi all, I'm just trying out Pro Tools Ultimate with 28day trial, & wanted to find the best way test total I/o latency, compared to my TDM rig.

I can obviously read the theoretical specs online, & of course just *listen*, but I'd like to know 'scientifically' what I'm dealing with .

Rig#1 is a TDM system running PT 10 HD
Rig#2 is a Pro Tools Ultimate 2020 software with a Firewire interface (yes I'm testing this on an old 5.1 Mac pro). I'd prefer to to it with a Native Pcie card & connect it to the same pair of AVID I/O units, but that's all I have for now.

Should I be physically patching an output back to an input, playing (for instance) a snare sample out, then looking at the gap between the two, in order to measure total round trip?

is there a better way?

Cheers