[moomin]

More, the speed of light puts a hard cap on how simultaneous you can be. Wolfram Alpha reckons New York to London is 19ms in a vacuum, more using fibre.

Going off on a tangent: Back in the days of Live Aid, they tried doing a transatlantic duet. Turns out it’s literally physically impossible because if A songs when they hear B, then B hears A at least 38ms too late, which is too much for the human body to handle and still make music.

[recursive]

It's a less hard problem than the duet. If the round-trip is 38ms, you can estimate that the one-way latency is 19ms. You tell the the other client to play the audio now, and you schedule it for 19ms in the future.

That's assuming standard OS and hardware and drivers can manage latency with that degree of precision, which I have serious doubts about.

In a duet, your partner needs to hear you now and you need to hear them now. With pre-recorded audio, you can buffer into the future.

[moomin]

You’re right that it’s an easier problem, but it’s still trickier than it looks. Remember the point of this is to be listening together. To do that, you need to be able to communicate your reactions. And then you’re back to the 38ms (in practice it’s probably twice that). Either way, at 120bpm that’s over a bar!

If you _don’t_ have real time communication, then you don’t really need to solve this problem. But the problem is fundamentally unsolvable because the speed of light (in a vacuum) is the speed of causality and, as I say, puts a hard cap on simultaneity. This tends to be regarded as obvious at interstellar distances but it affects us at transatlantic distances too.

[recursive]

You're basically right, but one 4-beat bar @120bpm is 2000ms.

Also latency demands on conversation are not nearly as tight as those on music performance. See ubiquitous video conferences.

[moomin]

My brain ain't working, and yeah, I don't tend to notice transatlantic delays on voice and video calls.

[amluto]

> More, the speed of light puts a hard cap on how simultaneous you can be.

Special relativity does indeed have something to say about simultaneity.

> Wolfram Alpha reckons New York to London is 19ms in a vacuum, more using fibre.

And this is not, in any respect, a limit on simultaneity. If the endpoints are moving at very very very quickly relative to each other, then there are complications. Otherwise you measure that 19ms or so and deal with it.