Just measured my 2 laptops and the Raspberry Pi 3 B+ with jack_iodelay. All @ 48000/256/2 through Audiobox 96 USB interface
Thinkpad carbon x1 i5-5300U CPU @ 2.30GHz, 8 GB ram
1326.281 frames 27.631 ms total roundtrip latency
extra loopback latency: 558 frames
Thinkpad e420s i5-2430M CPU @ 2.4GHz, 6 GB ram
1274.828 frames 26.559 ms total roundtrip latency
extra loopback latency: 506 frames
Raspberry Pi 3 B+ (stock raspian)
4589.929 frames 95.624 ms total roundtrip latency
extra loopback latency: 1517 frames
Raspberry Pi 4 B (stock raspian)
1256.920 frames 26.186 ms total roundtrip latency
extra loopback latency: 488 frames
Looks like the Raspberry Pi 3 B+ is a little more than 3x worse than the laptops. I’ll post another measurement when I get the Pi 4.
Edit: Just discovered that the speakers I was using (integrated into a TV set) were adding significant latency. Plugged in one of these laptops (which I tested earlier to be fine) and could definitely hear lag. Moved the patch cable to an external amp and it was fine. I guess the TV set has some internal analog to digial conversion with significant lag. This means I need to retest the Pi 3 B+.
Edit 2: The TV was not involved in the jack_delay measurements above. By “retest the Pi” I mean my previous audible test was through the TV and I need to retry that through a normal set of speakers.
Edit 3: Should be noted the laptops were running on a lowlatency kernel. The raspberry pi was running on “stock” raspian.
Edit 4: In a shock twist, running the raspberry pi (and Audiobox A96) through a real speaker (instead of the laggy TV speakers) the latency was acceptable. I think I could detect it very slightly but that could be in my head. It was extremely minor, if any. Stability of Jack/Ardour/GuitarixLV2 was bad at 128/2/48000, though. I have high hopes for the Pi 4.
Edit 5: Added results for Raspberry pi 4 B.