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We compare products from their published specs and features; the verdicts below are our independent editorial opinions.
If you want unlimited playtime and a plug-and-play USB-C signal chain that puts a real DAC inside the earbud, choose Hidizs ST2; if you need a flat, neutral wired monitor for studio mixing, tracking and DJ work, choose Audio-Technica ATH-M40x.
• Hidizs ST2 — biggest strength: A built-in ESS ES9218AC Pro DAC decodes up to 32-bit/384kHz PCM plus DSD128 and 8X MQA straight from a USB-C port, so the "source" lives inside the earbud. No amp, no dongle, no battery to charge.
• Hidizs ST2 — biggest trade-off: It is a wired USB-C in-ear monitor, so it is tethered to a device with a USB-C port, and its sound-isolation approach is in-ear sealing rather than over-ear cup isolation.
• Audio-Technica ATH-M40x — biggest strength: A flat, accurate 40mm dynamic driver tuned across 15Hz–24kHz, over-ear closed-back cups, 90° swiveling earcups for one-ear monitoring, and two detachable cables with a 1/4" adapter.
• Audio-Technica ATH-M40x — biggest trade-off: It needs a proper output — the 3.5mm plug and 1/4" adapter mean you supply the source, and there is no inline DAC or mic in the spec sheet.
• Who each pick is for: The ST2 is for listeners, gamers and mobile/desktop users who want audiophile decoding with zero battery anxiety; the M40x is for producers, engineers and DJs who want a neutral reference and one-ear monitoring.
The ST2 is essentially a tiny hi-fi rig folded into an earbud. Inside sits an ESS ES9218AC Pro DAC rated for 32-bit/384kHz PCM, DSD128 and 8X MQA unfolding, with 122dB dynamic range and 0.0012% THD. That combination matters for one practical reason: your phone, tablet or laptop stops being the weak link. Plug into USB-C and the conversion happens right at your ear, which is why the spec sheet can promise lossless playback from services like TIDAL and Spotify without an external box.
The acoustic side is a dual 10mm titanium dynamic driver with a PU+PEEK composite diaphragm, a dual magnetic circuit, 32Ω impedance and 118dB sensitivity, covering 20Hz–40kHz. The dual magnetic circuit is there to raise efficiency, extend the top end and cut distortion — which is exactly what you want if you listen across genres rather than one narrow band. A 32Ω load is also easy to drive, so it plays nicely with the kind of modest outputs you find on phones and laptops.
Then there are the quality-of-life details. There is a HD mic that converts mic audio to 24-bit/48kHz, inline volume control on the cable, a sample-rate indicator that lights differently per sample rate so you can see what your source is actually feeding it, and an OFC braided cable that resists tangling. The housing is skin-friendly German-imported resin with oval earpieces and silicone tips, and it ships with three pairs of silicone tips, a pouch, a USB-C to USB-A adapter and a warranty card. Compatibility runs across Windows, macOS, iOS, Android and HarmonyOS.
Buy the ST2 if you want monitor-grade decoding on the move, zero charging, and a mic for calls — gaming, streaming, coding sessions, commuting, coffee-shop listening. Skip it if your gear has no USB-C port, or if you specifically need the over-ear cup isolation and swiveling earcup of a studio can.
The M40x is the opposite philosophy: instead of building the electronics into the headphone, it builds the headphone to reveal whatever you feed it. The 40mm dynamic drivers use rare earth neodymium magnets and copper-clad aluminum wire voice coils, tuned to a flat, accurate 15Hz–24kHz response. "Flat" is the operative word — this is a monitoring tuning, not a consumer bass boost, and that is precisely what you want when you are judging whether a mix translates.
The physical design is aimed at working professionals. Over-ear closed-back cups isolate you from the room, which is the point in a noisy space or a live venue. The headband and earpads get pro-grade cushioning to reduce fatigue over long sessions, and the frame folds for transport — it ships with a carrying case in this bundle, along with a headphone stand, a microfiber cleaning cloth and a bottle of headphone cleaner. The 90° swiveling earcups enable one-ear monitoring, the move every DJ and tracking engineer relies on to hear the room and the cue mix at once.
Connectivity is where it separates itself from a consumer headphone. You get two detachable single-sided cables — a coiled 3.9 to 9.8-foot one for studio flexibility and a straight 9.8-foot one for desktop or mobile use — each with gold-plated 3.5mm plugs and a screw-on 1/4" adapter. That means it plugs into interfaces, mixers, headphone amps and phones without hunting for adapters.
Buy the M40x if you mix, track, DJ or do critical listening and want a neutral reference plus one-ear monitoring. Skip it if you want an inline DAC, a built-in mic or a cable-free-from-charging setup — none of that is in this spec sheet, and it is a wired 3.5mm headphone.
• Best for studio mixing and critical listening → Audio-Technica ATH-M40x. A flat 15Hz–24kHz response is the whole point of a monitor.
• Best for gaming with zero latency → Hidizs ST2. A wired USB-C DSP path and unlimited playtime beat any wireless setup for delay-free audio.
• Best for one-ear monitoring and DJ work → Audio-Technica ATH-M40x. The 90° swiveling earcups exist for exactly that.
• Best for phone and laptop listening without extra gear → Hidizs ST2. The DAC is inside; nothing else to buy or charge.
• Best for calls and voice chat → Hidizs ST2. It has an HD mic that converts audio to 24-bit/48kHz — the M40x has no mic in its spec sheet.
• Best for cable versatility → Audio-Technica ATH-M40x. Two detachable cables plus a 1/4" adapter cover studio and mobile rigs.
• Best for long sessions in a noisy room → Audio-Technica ATH-M40x. Over-ear closed-back cups plus cushioned headband and pads.
• Best for hi-res formats like DSD and MQA → Hidizs ST2. DSD128 and 8X MQA unfolding are built in.
If I had to pick one, I would buy the Audio-Technica ATH-M40x — because a flat, accurate monitor with one-ear monitoring and two detachable cables is a tool that stays useful for years, and it does not care what phone you own next. That said, my honest read is that this is less about which is "better" and more about which job you have: for pure listening, gaming and portable hi-res, I would take the Hidizs ST2 without hesitation. Buy the M40x to work; buy the ST2 to listen. Check the current price on Amazon before you commit, since both sit in different budget brackets depending on the bundle.
how to check headphones battery on iphone
This mostly applies to Bluetooth headphones, which report charge in iOS under Settings > Bluetooth next to the device name, and in the battery widget on your home screen. Neither headphone here is a Bluetooth model: the Hidizs ST2 draws power over USB-C and the ATH-M40x is a passive wired headphone, so there is no battery to check on either. If a battery indicator is what you are after, that is a wireless-headphone feature, not a monitor-headphone one.
how to check headphones battery
On wireless models you check remaining charge through the companion app, the phone's Bluetooth menu, or a voice prompt on the headset itself. The Hidizs ST2 has no battery — it is powered by the USB-C port it plugs into, which is why the spec sheet describes unlimited playtime. The ATH-M40x is also passive and wired, so there is simply nothing to charge or monitor.
how to check headphones
To check whether a wired headphone is working, plug it in, play a known track, and confirm both channels and the inline controls respond. On the Hidizs ST2 you can also watch the sample-rate indicator, which lights up differently per sample rate so you can see what your source is sending. On the ATH-M40x, swap between the coiled and straight detachable cables to rule out a bad cable before blaming the drivers.
how to check headphones mic
Test the mic in your operating system's sound settings by selecting the input device and watching the level meter while you speak. The Hidizs ST2 has an HD mic that converts voice to 24-bit/48kHz, so it should appear as a selectable USB-C input on Windows, macOS, iOS or Android. The Audio-Technica ATH-M40x has no microphone in its spec sheet, so there is nothing to test — you would need a separate mic.
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