How We Research
We compare products from their published specs and features; the verdicts below are our independent editorial opinions.
If you want a travel-first transmitter that gets aptX HD and aptX Adaptive audio out of a plane's 3.5mm jack and into your own earbuds or headphones, choose Avantree Relay & Voyager; if you need a USB-C dongle that turns your computer, laptop, phone or PS5 into an aptX HD and Auracast broadcaster, choose SUNITEC Auracast Transmitter USB-C. That's the short version for anyone pairing either one with aptx hd earbuds for computer use or for the tray table on a long flight. The two devices look similar on paper — both lean on Qualcomm-era codecs, both are small, both are plug-and-play — but they solve completely different problems, and picking the wrong one means paying for a feature you'll never touch.
• Avantree Relay & Voyager — biggest strength: a 3.5mm AUX input plus Bluetooth 5.3 output, with aptX Adaptive and aptX HD, so anything with a headphone jack becomes a wireless source for your own earbuds or headphones.
• Avantree Relay & Voyager — biggest trade-off: it's built for AUX sources only. Avantree's own spec sheet says it is not compatible with phones, car stereos or hearing aids, so it is not a general-purpose computer dongle.
• SUNITEC Auracast Transmitter USB-C — biggest strength: a single USB-C plug that switches between Classic Bluetooth and Auracast broadcast, with aptX HD, aptX Adaptive and LC3, and a broadcast range up to 164ft / 50m.
• SUNITEC Auracast Transmitter USB-C — biggest trade-off: audio playback only. There is no microphone input and no voice chat support, so it will not carry your voice on a call.
• Who each pick is for: Avantree Relay & Voyager for flyers and gym users who want their existing headphones working off a wired jack; SUNITEC for anyone who wants their USB-C computer, tablet or console streaming wirelessly — and optionally to many listeners at once.
The Relay is a one-job device, and it does that job well. You plug it into a 3.5mm AUX jack — the seat-back entertainment system on a plane is the obvious example — and it streams that audio over Bluetooth 5.3 to your own headphones or earbuds. The Qualcomm chipset inside supports aptX Adaptive and aptX HD, plus aptX Low Latency, so with a compatible listening device you get high-quality audio without the lip-sync drift that plagues cheap transmitters. Avantree lists AirPods, Bose and "all Bluetooth headphones" as compatible, which tells you the intent: this is for the traveler who already owns good headphones and refuses to use the airline's.
The controls are where it earns its keep on a long trip. Built-in buttons handle volume, pairing, reconnecting and clearing the pairing history, and an OLED display shows battery level and connection status — no guessing whether it died somewhere over the Atlantic. LED indicators back that up. It's battery powered, pocket-sized and light, which is exactly what you want in a bag that's already overstuffed.
SUNITEC Auracast Transmitter USB-C: Who It's For
The SUNITEC BT400T is a USB-C dongle, and its whole pitch is breadth. Plug it into a USB-C port on a PC, MacBook, laptop, tablet, iPhone 15/16/17, Android phone or PS5 and it transmits audio wirelessly — no drivers, no app. It supports AAC, SBC, aptX, aptX Adaptive and aptX HD in Classic Bluetooth mode, and LC3 in Auracast mode, which makes it one of the more codec-flexible dongles in this category. That matters if you're chasing aptx hd earbuds quality on a computer, because aptX HD is the ceiling you actually want.
The headline feature is the Auracast side. One button flips between Classic Bluetooth and Auracast broadcast. In Classic mode you pair a single headset and get roughly 33ft / 10m of range. In Auracast mode that jumps to about 164ft / 50m, and you can broadcast to virtually unlimited compatible Auracast headphones, speakers and hearing aids at once — with those devices discovering and joining the stream without pairing. There's also a 24kHz / 48kHz sampling switch: 24kHz (orange LED) is tuned for compatible Auracast hearing aids, 48kHz (green LED) for Auracast headphones and speakers.
Then the caveats, which are significant. SUNITEC states plainly that the BT400T is playback only — no microphone input, no voice chat. On PS5 you'd have to route voice through the controller's mic instead. And Auracast mode is only useful if your receiving gear actually supports Auracast or LE Audio.
Who should buy it? Gamers on PS5 or PC who want their Bluetooth headphones in the mix with low-latency aptX Adaptive; laptop and tablet users who want wireless audio without a dongle-hopping mess; and anyone doing one-to-many audio — classrooms, conferences, gyms, museums, family movie night, assistive listening. Who should skip it? Anyone who needs to talk, not just listen. If your day is full of calls, look elsewhere, because this dongle will carry the soundtrack but not your voice. It's also not a travel-jack solution — there's no AUX input here, so an airplane seat-back port is out of reach.
• Best for airplane seat-back audio → Avantree Relay & Voyager. AUX input, OLED battery readout, aptX Adaptive and HD out. That's the entire design brief.
• Best for aptX HD on a computer → SUNITEC Auracast Transmitter USB-C. USB-C in, aptX HD and aptX Adaptive out, no drivers needed. The cleaner match for a laptop or desktop.
• Best for low-latency gaming → SUNITEC. AptX Adaptive and aptX HD are called out specifically for keeping gameplay and sound in sync, and PS5 is a named use case.
• Best for range → SUNITEC. Up to 164ft / 50m in Auracast mode versus roughly 33ft / 10m in Classic — versus Avantree's travel-scale Bluetooth 5.3 link.
• Best for one-to-many audio sharing → SUNITEC. Virtually unlimited Auracast receivers at once, no pairing required.
• Best for plugging into gear that already has a headphone jack → Avantree Relay & Voyager. That's the only way it takes input.
• Best for hearing-aid users → SUNITEC, specifically its 24kHz Auracast mode for compatible hearing aids. Avantree explicitly excludes hearing aids.
• Best for a travel bag → Avantree Relay & Voyager. Pocket-sized, battery powered, built for flights and gym sessions; SUNITEC needs a USB-C host to do anything.
• Best for call and voice-chat duty → neither, honestly. Avantree is AUX-only and SUNITEC is playback-only. If you need a bluetooth headset microphone for computer calls, buy a headset that handles that natively, or pair your earbuds directly to the machine.
In my opinion, if your goal is aptx hd earbuds working wirelessly from a computer, the SUNITEC Auracast Transmitter USB-C is the one I'd buy. It plugs into the USB-C port you already have, covers aptX HD and aptX Adaptive, adds LC3 and Auracast broadcast, and doesn't need drivers. The lack of mic support is a real limitation, but for listening it's the more versatile tool. I'd only pick the Avantree Relay & Voyager if my actual problem were a 3.5mm jack on a plane or gym machine — it solves that beautifully and nothing else.
which earbuds support aptx hd
Earbuds that support aptX HD will do so only if their own chipset includes it — the transmitter can't add a codec the earbuds don't decode. Both transmitters here offer aptX HD (plus aptX Adaptive), so the deciding factor is your earbuds, not the dongle. Check your earbuds' spec sheet for aptX HD before assuming you'll get it.
Neither one handles voice. SUNITEC states the BT400T supports audio playback only, with no microphone input or voice chat, and Avantree's Relay is an AUX-input transmitter aimed at headphones. If calls matter, rely on your earbuds' own mic or your computer's built-in one instead.
Yes, if your iPhone has USB-C — SUNITEC lists iPhone 15/16/17 support. There's one quirk: if your headset doesn't connect within about 15 seconds, start playing music first to trigger transmission. No drivers or apps are required.
No. Avantree's spec sheet says the Relay is not compatible with phones or car stereos, and its input is a 3.5mm AUX jack rather than USB. For a computer you want the USB-C route, which is SUNITEC's territory. For a multipoint kids headphones for computer setup, pair the headphones directly to the machine rather than through either adapter.
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