ESI xKey 37 USB MIDI Controller Keyboard with Polyphonic Aftertouch

In a compact home studio or on a cramped tour bus, the ESI xKey 37 gives keyboard players and producers a full-featured MIDI controller that fits in a backpack. Its 37 full-size, velocity-sensitive keys with polyphonic aftertouch deliver expressive control, while the brushed aluminum chassis keeps it slim and road-ready. Connect via USB to macOS, Windows, iOS, or Android and start playing immediately—no drivers needed for most systems.

Key specifications

• 37 full-size, velocity-sensitive keys with polyphonic aftertouch
• Ultra-slim brushed aluminum body, only 13 mm thick
• USB-MIDI class compliant (Micro USB port), bus-powered
• Optional 5-pin MIDI output via Xkey-CBL-DIN cable (sold separately)
• Controls: octave up/down, pitch bend, modulation, sustain, and assignable buttons
• 16 MIDI channels, multiple velocity curves adjustable via Xkey Plus app
• Firmware upgradable; plug-and-play with macOS, Windows, iOS, Android
• Bundled with Bitwig 8-Track DAW software

Why choose it

The xKey 37 stands out for its polyphonic aftertouch—a rare feature in this price range—letting you add vibrato or filter sweeps per note. The full-size keys feel familiar to pianists, yet the entire unit weighs less than a kilogram. Its aluminum top plate resists flex and looks professional on any desk or stand.

Ideal use cases

• Mobile music production with a laptop or tablet
• Live performance where space and weight are limited
• Studio work requiring expressive MIDI control without a large footprint
• Educational settings needing durable, easy-to-connect keyboards

Good to know

The xKey 37 is USB bus-powered, so no external power supply is needed. For connecting to hardware synths or older MIDI gear, use the optional Xkey-CBL-DIN breakout cable. The Xkey Plus configuration app (free download) lets you customize velocity curves, assign buttons, and update firmware. Note that the sustain pedal input is available only via the optional cable.