Headset Jack Standards

There are two common arrangement for a four conductor point headset. The first, known as American Headset Jack (AHJ) standard or sometimes CTIA, has the microphone connector point on the sleeve end, with the signalling (or ground) connector on the second ring. This arrangement is used by most newer smartphones. Apple uses a similar connector arrangement, but uses a non-standard microphone and control signalling method.

The second common arrangement is the OMTP standard. It has the signalling connector (ground) next to the sleeve, with the microphone connector on the second ring. This is the reverse of the AHJ arrangement. It is used by older smartphones.

Plugging an OMTP headset into an AHJ jack, and vice versa, will result in the audio-out being inaudible or very quiet. Converters to switch between the two types of headsets are readily available, but do add extra bulk, and may not work reliably with remote control functionality.

Pin	AHJ/CTIA Description	OMTP Description
1	Microphone	Ground
2	Ground	Microphone
3	Right Ear	Right Ear
4	Left Ear	Left Ear