We compare products from their published specs and features; the verdicts below are our independent editorial opinions.
Updated: 2026-09-17 · 7 min read · Independent comparison
If you want flat, neutral studio monitoring with swiveling earcups and a proper over-ear fit, choose Audio-Technica ATH-M40x; if you need plug-and-play USB-C hi-fi with a built-in DAC, a mic, and no battery to worry about, choose Hidizs ST2.
• Audio-Technica ATH-M40x — biggest strength: 40mm dynamic drivers tuned flat across 15 Hz–24 kHz, with a circumaural closed-back design built for isolation and accurate monitoring.
• Audio-Technica ATH-M40x — biggest trade-off: It's a wired analog headphone with no DAC, no mic and no in-line controls, so you need a decent source and you can't take calls on it.
• Hidizs ST2 — biggest strength: A full ESS ES9218AC Pro DAC inside a USB-C in-ear, decoding up to 32-bit/384kHz PCM, DSD128 and 8X MQA with a 20 Hz–40 kHz range.
• Hidizs ST2 — biggest trade-off: In-ear fit is personal and the USB-C termination locks you to devices with a USB-C port (an adapter is included for USB-A), so older 3.5mm-only gear is out.
• Buy the Audio-Technica ATH-M40x if you mix, track or monitor and want one pair of over-ears that isolates well and swivels for one-ear work.
• Buy the Hidizs ST2 if you want better-than-Bluetooth sound straight out of a phone, laptop or handheld with a mic for calls and zero latency for games.
The ATH-M40x is a monitoring tool first. Its 40mm drivers use rare earth magnets and copper-clad aluminum wire voice coils, and the tuning is deliberately flat across 15 Hz–24,000 Hz with 98 dB sensitivity. That combination is the whole point: you're not buying these for a fun, bass-forward signature. You're buying them so what you hear resembles what's actually in the file. If you're tracking vocals, editing a podcast or checking a mix, that neutrality is worth more than any "exciting" tuning.
The physical design backs that up. The circumaural cups contour around the ears rather than pressing on them, which gives real sound isolation in loud rooms and keeps bleed down. The earcups rotate 90 degrees, so you can flip one cup off for single-ear monitoring while you record. The headband and earpads use professional-grade materials, and the whole thing collapses for transport. In the box you get a coiled cable (roughly 3.9 to 9.8 feet), a straight 9.8-foot cable, a screw-on 1/4-inch adapter and a carrying pouch — and this particular bundle adds a desktop headphone stand and a cleaning cloth.
Hidizs ST2: Who It's For
The ST2 is a different philosophy entirely. It's an in-ear monitor with the DAC built into the cable — specifically an ESS ES9218AC Pro chip that handles up to 32-bit/384kHz PCM, DSD128 and 8X MQA unfolding. The numbers Hidizs publishes are serious for a dongle-free setup: 122 dB dynamic range, 0.0012% THD, and 70mW×2 of output power. In practice that means you can plug it into a phone, tablet, Mac, PC or handheld over USB-C and get decoding quality that usually requires a separate DAC/amp box. A sample-rate indicator on the cable even lights up differently depending on the stream, which is a nice touch for spotting whether you're actually getting hi-res.
The driver side is a dual magnetic circuit feeding a 10mm dynamic driver with a PU+PEEK composite diaphragm, rated 20 Hz–40 kHz at 118 dB sensitivity and 32Ω impedance. The 32Ω figure is the practical one: it's easy to drive, so you don't need a powerful source. The housing is skin-friendly German-imported Byer resin, the cable is braided OFC for tangle resistance, and the package includes three pairs of silicone tips, a pouch, a USB-C to USB-A adapter, and a warranty card. There's an HD mic that converts voice to 24-bit/48kHz, plus touch volume controls and in-line control.
Who should buy it: mobile listeners who want lossless-ish audio without carrying a dongle DAC, gamers who care about latency (USB-C wired means essentially none), people on long calls who want a clear mic, and anyone tired of charging wireless buds. Who should skip it: anyone who dislikes in-ear tips, anyone whose main device is 3.5mm-only, and anyone who needs the isolation and swivel of a proper over-ear for tracking. The 1-year warranty is also shorter than the M40x's limited 2-year coverage.
• Best for studio monitoring and mixing → Audio-Technica ATH-M40x. Flat tuning and closed-back isolation are the point.
• Best for phone/laptop listening without extra gear → Hidizs ST2. The DAC is inside the cable.
• Best for gaming with no latency → Hidizs ST2. Wired USB-C and a 20 Hz–40 kHz range with a sample-rate indicator.
• Best for calls and voice chat → Hidizs ST2. It has an HD mic and in-line controls; the M40x has neither.
• Best for long wear in a loud room → Audio-Technica ATH-M40x. Circumaural cups around the ears isolate better than tips for many people.
• Best for portability and durability → Audio-Technica ATH-M40x. It collapses, ships with two cables and a pouch, and carries a 2-year limited warranty.
• Best for fit flexibility → Hidizs ST2. Three sizes of silicone tips let you tune the seal; over-ears are one-size.
• Best for high-resolution file playback → Hidizs ST2. Native 32-bit/384kHz, DSD128 and 8X MQA support beat what a plain 3.5mm analog output gives you.
If I had to pick one, I'd buy the Audio-Technica ATH-M40x. In my opinion it's the more versatile tool: it works with almost any source via 3.5mm or the included 1/4-inch adapter, it isolates, it swivels for one-ear work, and it collapses into a bag. The flat tuning also holds its value over time — it stays useful whether you're mixing or just listening critically. I'd only steer you to the Hidizs ST2 if your life happens on USB-C devices and you specifically want a built-in DAC, a mic and zero-latency gaming in a pocketable in-ear. That's a real, valid set of needs — just narrower.
For mixing, yes, in my opinion. The M40x is tuned flat across 15 Hz–24 kHz with a circumaural closed-back design meant for isolation, which is exactly what monitoring calls for. The ST2 is a hi-fi listening and gaming IEM first.
Does the Hidizs ST2 need an amplifier or a dongle?
No. The ESS ES9218AC Pro DAC is built into the cable, so it runs straight from a USB-C port. A USB-C to USB-A adapter is included for computers that only have USB-A.
Not really. It has no microphone and no in-line controls — it's a pure monitoring headphone with a 3.5mm/6.35mm wired connection. The Hidizs ST2 is the one with the HD mic and touch controls.
It depends on your preference. The M40x uses circumcural earpads and professional-grade headband material for extended wear; the ST2 uses skin-friendly resin housings and three sizes of silicone tips. If you dislike things in your ears, go with the M40x.
Whichever you lean toward, check the current price on Amazon before you commit — the numbers move, and both are sold as single units with different accessory bundles.
As an Amazon Associate I earn from qualifying purchases.
We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon and affiliated sites.
When you buy through links on this page, we may earn a commission from qualifying purchases at no extra cost to you.
Amazon and the Amazon logo are trademarks of Amazon or its affiliates. This site is an independent third-party review and is not affiliated with, endorsed by, or sponsored by Amazon or the product brands mentioned.