There are several kinds of earphone interfaces.

Headphone interface specifications are 3.5MM and 2.5MM, and the 3.5MM interface specification is a universal headset interface.

Headphones are divided into two standards: OMTP standard is usually called national standard and CTIA is called international standard. The difference between them lies in the reverse order of GND and MIC in the last two paragraphs of the plug. CTIA headphones are compatible with OMTP devices. When CTIA headphones are plugged into OMTP equipment, the sound will be very small and distorted, and the sound will be restored after pressing MIC key. It can be concluded that the device is OMTP standard and the earphone is CTIA standard.

2.OMTP is a 3.5mm interface standard for headphones with MIC, which is usually called the national standard and used by the country. The pin connection mode is (from the small head): left channel-right channel-microphone-ground wire.

3. There is also a headset with 3.5mm interface with MIC, which is an international standard called CTIA. Pin connection mode: left channel-right channel-ground wire-microphone.

Extended data:

2.5mm TRS interface used to be popular on mobile phone headphones, but now it is rare, and the headphone interface is mainly 3.5mm interface. 6.3mm interface is common in many professional devices and high-end headphones, but now many high-end headphones are gradually switching to 3.5mm interface. TRS means tip (signal), ring (signal) and sleeve (ground), which respectively represent the three contacts of this joint. What we see are three metal columns separated by two insulating materials. Therefore, the 3.5mm joint and the 6.3mm joint are also called "small three cores" and "big three cores".