The Web Morse player and subsidiary pages (Koch trainer, Morse Hero) got an "improvement": background noise. Strange as it seems, it sounds more natural and even easier to pay attention to (at least for me), perhaps because it helps to mask the real-world noise. Another minor improvement is the addition of some second harmonics. This gives some tone color to the beeps.
Currently, the Morse beeps are generated by a) pre-generating sound buffers with dots and dashes, and b) play these buffers at scheduled moments. This approach is very efficient, but not very flexible. Introducing other distortions like tone/volume oscillation, faint CW signals from other stations, etc. will demand real-time Morse generation. If time allows, I intend to do this move in the next few days.