how responsive is the iOS screen?

I'm experimenting with my ipad as a music controller, and finding that there's too much latency with touchesBegan events for it to work we开发者_运维百科ll as a responsive-feeling percussion controller.

Am I doing something wrong, or is this a limitation of the devices. Which factors effect the amount of time that elapses between my finger touching the screen and the touchesBegan event firing?

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It is much much less than 250 ms. I experience in the range of 25 - 50 ms for most events on the iPad -- which, unfortunately, is only fast enough to coarsely represent events on the scale of percussion. Sure a percussionist usually doesn't diddle 20 times a second (sometimes they do) but even if they don't, sampling theory explains why the iPad (or any of its late-to-the-game contemporaries) can't represent the timing accurately.