Why gadgets (earphones and player) with the function of active noise control have long existed, but a separate module of the ACP no?

ASHP is not a universal silver bullet, it is strongly tied to specific design and components of the headphones. Transplanted to the other conditions of the ACP will not work.

gadgets (earphones and player) with the function of active noise control have long existed

Well, well... Another victim of smart-ass marketers.

Well, how would the technology - the microphone in the ears catches things that want to fly in your ears and gives you the headphones the opposite. In the end, zero.

I don't know anything about iPods noise cancelling, a rather gloomy concept, it turns out, the microphone should be on the player and how he will distinguish the rustling of pants from this noise I don't know... But the ears with the active noise cancelling is.

On the question of technical implementation, here's a link to Banny but warming my soul service lmgtfy.com/?q=diy+active+noise+cancelling