An Apple patent application covering a wireless hybrid headphone system was published by the U.S. Patent and Trademark Office on Thursday, suggesting the company is continuing work on a Lightning-equipped audio product some expect will replace wired EarPods if and when iPhone ships without a 3.5mm headphone jack.

As published, Apple's patent application for "Audio class-compliant charging accessories for wireless headphones and headsets" details a headphone device and supporting hardware capable of seamlessly switching between wired and wireless listening modes.

Unlike traditional headphones that terminate in a 3.5mm TRRS (tip, ring, ring, sleeve) plug, Apple's invention employs an electrical connector compatible with both digital and analog signals, requirements the proprietary Lightning protocol satisfies. An ideal connector would employ a plurality of contacts to transfer power and audio data — via differential signaling — from a host device to the headphone. This arrangement allows for a single cable to both charge and control the device, eliminating the potential for ground loops that compromise audio fidelity.

In addition to wired contacts, Apple's proposed headphone includes an internal battery, processor, memory and antenna and wireless transceiver package for communicating with a user device. An iPhone, for example, is able to charge the headphone while being communicatively coupled to the device.

The key to Apple's invention is its handling of audio transmission signals. In practice, a user device communicates with the headphone both through wired and wireless interfaces, sending a packet of authentication data (including, but not limited to, audio) over for decision logic processing. This data is used by control circuitry to determine that the headphone connected via wired communication module is the same device as the headphone connected over wireless.

When a successful match is found, audio data sent to the headphone device via wired or wireless communications module is collected in a hardware buffer, or onboard memory. The headphone is able to fall back on this buffered audio when a user switches from wired to wireless playback, or vice versa, an action that normally results in audio dropouts as the system re-establishes communications.

As for design, the document keeps things vague, noting all supporting hardware can fit into in-ear, on-ear and over-ear styles.

Whether Apple will incorporate the technology into a next-generation headphone is unclear. Last November rumors surfaced claiming Apple plans to remove iPhone's 3.5mm headphone jack in favor of a wireless or Lightning solution. The company already fields both wireless and Lightning-enabled audio equipment through its Beats by Dre lineup, but has yet to utilize similar technology in an equivalent Apple-branded product.