3.5 mm TRRS
Jack Connectors · 7 specs
Direct Answer
3.5mm TRRS connectors transmit stereo audio plus a microphone signal over four conductors. CTIA wiring places ground on Ring 2 and mic on the sleeve; OMTP swaps ground to the sleeve and mic to Ring 2, causing muted or distorted audio when the two are mixed.
Source: CTIA Specification · Last reviewed Aug 28, 2026
Specs
| Connector Family | Phone Jack (Mini-Jack) |
| Shaft / Plug Diameter | 3.5 mm (1/8") |
| Conductors / Contacts | 4 (Tip, Ring 1, Ring 2, Sleeve) |
| Signal Format | Stereo Audio + Microphone / Inline Remote |
| CTIA Standard Pinout | Tip: Left | Ring 1: Right | Ring 2: Ground | Sleeve: Mic (Apple, Android) |
| OMTP Standard Pinout | Tip: Left | Ring 1: Right | Ring 2: Mic | Sleeve: Ground (Legacy EU) |
| Primary Applications | Smartphone headsets, gaming headsets, laptops with combo audio/mic jack |
Why Two Competing Standards Exist
CTIA and OMTP emerged as competing wiring schemes for the same four-conductor 3.5mm plug. OMTP (Open Mobile Terminal Platform) was an industry initiative associated with Nokia and was common on early Nokia and Sony Ericsson handsets. CTIA, named for the US wireless trade association, became the wiring Apple adopted starting with the iPhone 3GS, and it's what nearly all modern phones and headsets use today.
The two standards only differ in where they put the microphone and ground conductors, but that's enough to break compatibility: because ground and mic are swapped, plugging a CTIA headset into an OMTP device (or vice versa) typically leaves the microphone unusable, and can make audio come through quiet or distorted since the ground reference lands on the wrong contact.