[avisser]

For guitar pedals, there is an implied sub-perceptibility. The output needs to happen as I play - if the delay is too long, it's now a delay pedal.

So realtime might match your definition, but it is consistent in audio production.

For humans, you can start to notice the lag @ 50ms. (A selection of experimental results summarized here https://gamedev.stackexchange.com/a/74975)

[NobodyNada]

Latency is much more noticeable when you’re playing a musical instrument; 25-30ms is the point at which it becomes distracting in my (anecdotal) experience as a keyboardist. 50ms would be literally unplayable —- I cannot keep in time if latency is that severe. And that’s total output latency from the moment a key is depressed to the moment the sound comes out the speakers, so it’s important for every component in the signal chain to have the lowest possible latency. A bunch of 5-10ms delays adds up really quickly.

[mrob]

>50ms would be literally unplayable

You can learn to play it. Pipe organs routinely have more than 50ms latency just from the distance the sound has to travel from the pipes to the organist. Add the time needed to set up steady oscillations in large pipes, and the slow pneumatic actions found in some organs, and >200ms latency is nothing unusual. The important thing is that the latency is consistent.

[TheOtherHobbes]

1ms is usually considered inaudible. 5ms is bearable. 10ms will start to annoy some people. 25ms is actually pretty bad.

[strbean]

Throw on some headphones, and mix your clean signal with the rest of the ensemble on a 50ms delay.

(jk)