A TRRS or Tip Ring Ring Sleeve plug has four conductors and is very popular with 3.5mm, and can be used with stereo unbalanced audio with video… or with stereo unbalanced audio plus a mono microphone conductor. The TRRS connector is extremely popular with smartphones and tablets, and to some degree with computers, including Chromebooks and Macs. Unfortunately, there are two conflicting standards associated with its use with stereo unbalanced audio plus a mono microphone conductor.
The older OMTP wiring standard calls for Tip to be used for left audio, Ring 1 to be used for right audio, ring 2 to be used for microphone, and the sleeve to be used for ground. According to my research, this older OMTP standard is found in old Nokia (and also Lumia starting from the 2nd generation), old Samsung (2012 Chromebooks), old Sony Ericsson (2010 and 2011 Xperias), Sony (PlayStation Vita) and the OnePlus One I used to own before migrating to a Nexus 6 for use with Project Fi.
The newer CTIA/AHJ wiring standard reverses the last two mentioned, so it calls for Tip to be used for left audio, Ring 1 to be used for right audio, ring 2 to be used for ground, and the sleeve to be used for microphone. According to my research, this newer CTIA/AHJ wiring standard is used in products from Apple, HTC, latest Nokia, latest Samsung, Jolla, Sony (Dualshock 4), Microsoft (including Surface, Lumia, and XboxOne controller with chat adapter) and most Android phones. To that I will add that if you use an MXL microphone with TRRS with a supported Mac, in some cases you absolutely must connect a TRS stereo headphone into the TRS stereo jack which is part of the MXL microphone. Otherwise, the supported Mac will not realize that there is a mic connected. Apparently, with some of the supported Macs, it does not detect the presence of a TRRS plug, but also the impedance of the stereo headset plugged connectemm
