[rcfox]

The linked answer is close, but not entirely correct. There isn't a specialized wire for buttons; it uses the microphone line.

Play/pause will usually be connected directly to ground. The other functions connect to ground through different impedances. While each impedance level is roughly twice the last one (which makes the detection circuit simpler) having one level at 1 ohm and the next at 2 ohms is not practical due to noise. Also, due to the way that parallel impedances work, you do not get a binary encoding of the buttons pressed. (Do you ever really want to skip the track and increase the volume at the same time anyway?)

[abailin]

Would increasing the resistances to something more significant like 1k, 2k, 4k ohm make any difference wrt noise?

[rcfox]

Not really. You only need to space out the levels by a few ohms.

Microphone impedances start around 500 ohms, so if you go higher than that, you can't distinguish between a button and a working mic.

[kmm]

Thank you. I was wondering if such headphones with a microphone would need five connections.

[eidorb]

I guess you could use a series arrangement to get a binary encoding.