Taken from "Human factors of computing systems"

ABSTRACT

For years, software engineers have been told that applications must respond to user events within 100 milliseconds to seem instantaneous, yet this assumption has never been systematically tested. In this research, we attempt to establish thresholds of detection for changes in a graphical user interface using adaptive tracking. For keyboard interactions, subjects did not notice delays of approximately 150 milliseconds. In contrast, for mouse interactions, subjects did not notice delays of up to 195 milliseconds. Given these findings, further research is clearly needed to firmly establish lower bounds on application responsiveness so that software and operating system engineers can more precisely tune the interactive real-time responsiveness of their systems.

Jerry that isn't even close to the tolerance for music applications[software]..

I think you may be comparing apples to oranges here. The 1/4 sec latency has NOTHING to do with the time it takes for the sound to play after selecting the voice, but instead, the time it takes for the LISTING of available sounds to appear after pressing a 'voice bank (instrument family)' button. Once you select the actual instrument voice patch, the voice can be played & heard IMMEDIATELY (no delay/latency) whatsoever.

In live performance, where instant access is needed, selecting voices directly via voice 'instrument family' buttons doesn't make sense anyway, no matter which brand keyboard, because after selecting the appropriate voice family bank button, you'll often then need to open a subsequent page/window to find & then select the actual voice you want to play, and all that usually takes FAR LONGER than 1/4 second.

In addition, as I already thought I had clearly stated earlier in this thread, with all Yamaha arranger keyboards, selecting voices DIRECTLY from the voice 'bank buttons' merely calls up the instrument voice, with NO EFFECTS (reverb/chorus, etc) added, so not really suitable in that state for live 'on the fly' performance selection. I instead prefer & recommend storing personally tweaked voices (with reverb/chorus effects added) into reg and calling up live play instrument voices for 'instant access' on the fly performance selection that way. - Scott

[This message has been edited by Scottyee (edited 04-29-2006).]

The general rule for latency is understood to mean the time it takes from when you hit the key to when you hear the sound. This should be 10 ms or less.