I tried a loopback test in Audicity with my setup per: https://manual.audacityteam.org/man/latency_test.html
My computer is a 2017 MacBook Pro running High Sierra. I ran the tests after a restart of the computer with no other programs running.
Focusrite Scarlett 2i2 – 6ms.
Built in computer speaker and microphone – 27ms
Apple wired earbuds with built in microphone plugged into the computer’s audio jack – 20ms
This shows that this external audio interface performs much better than the built in audio. I had hoped that the built in sound card would provide equivalent results (for a less expensive solution), but this is not the case.
I found that the results were sensitive to buffer length settings in Audacity located at Preferences – > Devices. I used a 2.5ms for buffer length for all of these tests. This corresponds to roughly 32 frames per period at a sample rate of 44100.
Rerunning the test on the Scarlett 2i2 at 4.35ms (64 frames per period @44100) resulted in an 11ms latency
A smaller buffer length is desirable for less latency. At some point as the buffer length gets smaller the audio quality will suffer and the demands on the processor will go up substantially. I did not evaluate audio quality in these tests, though previously I have noticed occasional blips getting in my recordings if I went below 64 frames per period.