How to test a MIDI device
- Connect the keyboard, pad controller or interface, then press Start MIDI test and allow MIDI access when the browser asks. Chrome has asked for this permission on every MIDI page since version 125 (Chrome for Developers).
- Play something. The key or pad lights up with its velocity, the channel indicator flashes, and every message appears in the event log with its time, channel and raw bytes.
- For a full check, play every key once softly and once hard, move every knob, fader and wheel to both ends, press the pedals, and push the pitch bend fully both ways before letting go.
- Turn on Sound to hear the device through a built-in synth, or use the Output test to send notes to a synth or sound module.
Connecting over USB or Bluetooth
USB: most current keyboards and controllers are USB MIDI class compliant, so they work without a driver on Windows, macOS, Linux, ChromeOS and Android (with a USB-C or OTG adapter). If one doesn't show up, try another cable: charge-only cables are the most common cause. Some older or pro devices need the maker's driver.
Bluetooth: Bluetooth MIDI devices (the MIDI Association's BLE-MIDI specification) don't appear just by pairing them in the system's Bluetooth settings. On a Mac, open Audio MIDI Setup, choose Window › Show MIDI Studio, click the Bluetooth button and connect the device there. On Android, connect it with a Bluetooth MIDI app first. On Windows, browsers often can't see Bluetooth MIDI at all, so use USB there.
5-pin DIN: older gear connects through a USB MIDI interface. Its MIDI IN goes to the device's MIDI OUT, and the interface is what the tester lists.
Reading the results
- Dead keys: the number of keys (or pads) that have sent a Note On. A key that never registers, however you press it, has a failed contact or a broken connection on its board. If notes arrive from outside the range, set the keyboard size or use the octave buttons.
- Velocity range: the lowest and highest velocity, a histogram of everything you played, and a bar per key from its softest to its hardest note. A key that can't get loud has a worn contact; a key that always sends 127 or close to it usually has one of its two contacts dead, because velocity is measured as the time between them.
- Stuck notes: a note held for 8 seconds or more, or struck again without a Note Off in between. The MIDI 1.0 message summary allows a Note On with velocity 0 as a Note Off, and the tester treats it that way.
- Chatter and duplicates: a note re-fired within 30 ms (a bouncing contact or an oversensitive drum trigger), or an identical message within 3 ms, which almost always means a MIDI loop or the device connected twice.
- Knobs and faders: each control, named from the MIDI 1.0 Control Change table (1 is the mod wheel, 7 volume, 64 sustain), with the values it has reached. Pass means it covered 0 to 127 without jumping 20 or more in one step. Sustain and other pedals switch between 0 and 127; endless encoders send small steps and are recognised as such.
- Pitch bend: shown from −8192 to +8191 around the centre (the 14-bit value 8192). A healthy wheel reaches both ends and springs back to 0 or within a few steps of it.
Common faults and fixes
- A block of neighbouring keys, or a regular pattern such as every eighth key, is dead: keys are read in groups through a matrix, so this points to one of its lines, a cracked ribbon cable or a loose connector on the key bed, not to the keys themselves.
- One key is quieter or louder than the rest: dirt or wear on its rubber contact strip. Cleaning the contacts usually fixes it; the manufacturer or a repair shop can replace the strip.
- Sustain works backwards (notes hold when the pedal is up): the pedal's polarity doesn't match the keyboard. Flip the polarity switch on the pedal, or plug it in before switching the keyboard on so it can detect it.
- Everything is doubled: MIDI thru or echo is on in your DAW, or the device is connected over USB and a MIDI interface at once.
- The device works here but not in your music software: the hardware is fine. Check the MIDI input and channel settings in the program, and close other programs that may hold the port.
Testing a computer keyboard instead? Use the keyboard tester. To check the speakers you'll hear the synth through, try the speaker test, and to turn a recording into MIDI notes, the audio to MIDI converter.