MXR Turbo Tuner powered by Sonic Research

Let’s get one thing straight: a tuner is not the most glamorous pedal on your board. It won’t give you that extra bit of hair on your overdrive, make your solos sing, or turn your bedroom into Abbey Road. But when it comes to being in tune, you’d better get it right. And that’s where the new MXR M400 Turbo Tuner comes in.

This is MXR’s first-ever tuner pedal, and they certainly didn’t ease themselves into the game. For this one, they teamed up with Sonic Research, the name behind the legendary Turbo Tuner — a pedal that earned a serious reputation among professional players, studio musicians and tuning perfectionists who simply refuse to settle for “close enough.”

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A strobe tuner is more precise and responsive than a conventional tuner. Instead of relying on a needle or moving indicator, it uses a strobing display to show even the tiniest differences in pitch. This makes tuning faster and more accurate, especially when setting intonation or fine-tuning a guitar. For players who demand perfect pitch, a strobe tuner leaves little room for guesswork.

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The Sonic Research story

Sonic Research, founded by engineer Roger Schlichtig, built its reputation around one deceptively simple idea: make a tuner that gets the job done with extraordinary precision and virtually no lag. Its original Turbo Tuner became something of a secret weapon for players who take tuning, intonation and setup work seriously. No gimmicks, no unnecessary bells and whistles — just incredibly accurate tuning.

Now, that technology gets an MXR makeover. The M400 retains the core Sonic Research design, with MXR bringing its familiar pedal format and production muscle to the table. Think of it as a meeting between serious engineering and pedalboard practicality. A pretty good combination, if you ask us.

Precision you can actually see

At the heart of the M400 is a genuine strobe display with an astonishing ±0.02-cent accuracy. Forget the sluggish needle or vague little bouncing indicator. The LED strobe reacts immediately to your playing: sharp notes spin one way, flat notes spin the other, and as you approach perfect pitch, the movement slows until everything settles down.

It’s fast, intuitive and ridiculously precise. Whether you’re tuning before a gig, dialing in your intonation at the workbench, or getting that finicky vintage guitar to behave in the studio, the M400 gives you the confidence to get it right.

The display is bright enough for outdoor use, with four brightness settings for those darker stages and rehearsal rooms where you’d rather see your tuner than accidentally blind the drummer.

More than just standard tuning

Chromatic, guitar and bass modes are on board, alongside five customizable presets for your own tunings and instruments. Drop tunings, alternate tunings, instruments with up to 12 strings and even custom temperaments are all part of the deal. USB connectivity allows firmware updates and customization through the editor software.

And because a great tuner should fit your rig rather than dictate how you build it, the M400 offers switchable true bypass or buffered operation, with three buffered modes to suit different signal-chain needs. There's also a 9V power output for passing power to another pedal.

All of this comes packed into a rugged MXR enclosure that feels right at home on a serious pedalboard.

The MXR M400 Turbo Tuner isn't here to make a big song and dance about tuning. It's here to make sure you never have to. And if you're the kind of player who cares about every cent — literally — this little box deserves your attention.

Specs at a glance

• Model: MXR M400 Turbo Tuner

• Tuning system: True strobe

• Accuracy: ±0.02 cents

• Modes: Chromatic, Guitar, Bass and customizable presets

• Preset flexibility: Five customizable presets, supporting instruments up to 12 strings

• Custom tuning: Alternate tunings, offsets and temperaments

• Display: Bright LED strobe with four brightness levels

• Bypass: Switchable true bypass or buffered operation

• Connectivity: USB-C for firmware updates and editor software

• Power: 9V DC, with additional 9V power output

• Construction: Rugged MXR-style enclosure

The Guitar Bar verdict: You can get by with a lot of things in life. Being out of tune shouldn't be one of them.