[fho]

Not entirely sure what you are getting at, I am guessing "10 ms latency is good enough for audio"? Plus "normally we are so far away from the speaker that it does not really make a difference"?

That figure is thrown around a lot and is definitely grounded in some solid research ... just ... lower latency numbers (in jackd) "feel" better when playing guitar. There is a lot of subjectivity in the guitar playing world and I am definitely not immune to that.

So ... 2.8 ms round-trip time in jackd plus 1-2 ms for AD/DA conversion plus 3 ms that the sound takes to travel from the speaker to my ear (plus any latency that the brain needs to process the sound). 2.8 + 2*1-2 + 3 already gets us very close to 10 ms.

No idea what I am getting at here, but I am on my third generation of modelling amps (cheap M-Audio BlackBox, POD X3 Live, now Guitarix) and while I never really had an issue with the latency ... I feel like I probably would if I went back to a previous generation.

[namibj]

There is a lower threshold beyond which you won't feel the difference anymore.

Also, by replacing a speaker with headphones, there is enough latency budget from that that can be spent on lightspeed delay for 100+km distance, if optimizing the audio stack for deep-sub-millisecond delays using RT_PREEMPT. Yes, this precludes USB2, but modern computers have quite decent on-board audio codecs (aka A/D + D/A engines) that end up connected to the southbridge and are accessed via PCIe. That has sub-microsecond latency between the digital side of the A/D + D/A converters and the CPU cache.

I guess I mostly just wanted to say "RT_PREEMPT reduces jitter enough to allow sub-millisecond AD->jackd(mixer only)->DA without much effort using modern onboard audio", and to show that is truly little in sound wave path length.

[fho]

> replacing a speaker with headphones

That makes perfect sense! I am aware of the issue ... but apparently I never put two and two together there :-)

USB Audio 2.0 on USB 3.x is actually quite decent. But honestly I have no clue what actually changed there over USB Audio 1.0.

[namibj]

"the issue" refers to the audio latency of speakers, I assume? If not, please elaborate; my understanding of the matter in practical/human terms is fairly fuzzy due to most of this being very domain-specific knowledge I haven't been in the right places for.

Oh, I know USB-attached-SCSI (the good USB3 storage protocol) is nice in latency due to actually exploiting the dedicated TX/RX lanes for latency benefits. It just shoves command packets towards the drive, and receives response packets when the drive has them ready.

However, USB still has comparatively severe driver overhead due to the MMIO-level protocols, to a similar (but iirc worse) extend as AHCI (with NVMe being the better replacement).