See https://dl.dropboxusercontent.com/u/40949268/emcc/bugs/webaudio_only_sdl_beep.html. The 48KHz example is the most interesting one for this bug.

Weird. I've played a lot with sample accurate scheduling for musical applications and I have not observed such behavior, the playback was sample accurate all the time. I'll have a look.

The testcase in bug 913854 plays back fine with large enough buffering, so I suspect the issues here with 48kHz are just from not enough buffering. (I didn't work out what SDL.audio.samples was set to here.) For the other sample rates, duping to bug 913854, which links to another testcase, sharing much of this code, but with controls to tune the buffering.