Smartphone Headset Standards – AHJ (CTIA), OMTP

There are different types of 3.5mm TRRS smartphone headsets, and they are not compatible. The most common issue that causes compatibility issues is the number of conductor points on the headset and what they are connected to, but the signaling arrangement is also important.

Modern smartphones typically use smartphone headsets with four-conductor points. In almost all cases, two points are used for audio out (stereo), one for the microphone and one for signaling. However, these points are not always used in the same way or the same order.

There are two common arrangements 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 signaling (or ground) connector on the second ring. Most newer smartphones use this arrangement. Apple uses a similar connector arrangement but uses a non-standard microphone and control signaling method.

The second common arrangement is the OMTP standard. It has the signaling connector next to the sleeve, with the microphone connector on the second ring.
That is the reverse of the AHJ arrangement. Older smartphones use it.

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 add extra bulk and may not work reliably with remote control functionality.

AHJ/CTIA is used by: Apple, HTC, LG, Blackberry, latest Nokia, latest Samsung, Jolla, Sony (Dualshock 4), Microsoft (including Surface and XboxOne controller with chat adapter) most Android phones. Because this is the most compatible, most Headset Buddy products are CTIA unless otherwise stated.
OMTP is used by: old Nokia, old Samsung, old Sony Ericsson, Sony, OnePlus One.

Apple’s non-standard signaling and control method means many designed iPhone headsets are incompatible with other devices. In general, the audio out and one-button control on such headsets will work, but the audio-in (microphone) and volume controls will not. Some headset manufacturers produce dual version products with wider support but working out is a little hit and miss. It’s advisable to avoid iPhone-specific headset accessories where possible; instead, look for AHJ or OMTP compatibility as suited to your particular device.

An added complication is added in by how the signaling (remote control) element works. The AHJ standard has several defined shortcuts and the single button press (answer/end call or play/pause music). These include a long press for voice commands, a double press to skip forward a music track, and a triple button press to skip back a music track. These shortcuts do not always seem universally implemented, but there’s no particular pattern that can be recognized.