How to test polyphonic MIDI key input

You press a chord during piano practice, but one note seems to disappear, or the instrument plays notes that you did not mean to hold. Before changing your lesson software, check whether the keyboard is sending each key press and release as MIDI input.

The MIDI Test can show which notes arrive from a connected keyboard or controller. Use it to compare single notes, small chords, and larger groups, then narrow down whether the issue is the keys, the connection, or the software receiving the input.

Test notes played at the same time

1. Open the MIDI Test on a computer in a browser that supports MIDI. Safari does not support this test, so use Chrome or Edge instead.
2. Connect your digital piano or MIDI keyboard by USB, or connect it using its usual MIDI connection. If the browser asks for MIDI access, allow it. Select the keyboard in the test if there is more than one available device.
3. Press one key, hold it for a moment, and release it. Confirm that the test registers the note and then shows that it has ended. Repeat with a few keys across the range you use in lessons.
4. Play a two-note interval, then a three-note chord. Keep the notes down together for a moment. Check that each note appears, and release one finger at a time to see whether the remaining notes stay active.
5. Try a chord from your lesson, then a slightly larger group of notes. Repeat the same pattern several times. If you use a sustain pedal, test it separately after checking the keys without it.

For a careful two-key check, see how to test a MIDI keyboard with two keys held down. The important detail here is to check the whole chord and release each key separately, not just to listen for a sound.

What the result means

Every note appears and clears when released

The keyboard is sending the notes the browser receives, including simultaneous notes. If the chord still sounds incomplete in your lesson software, check that software's selected MIDI input and instrument settings. The MIDI Test checks incoming MIDI messages, not the instrument's audio output or the sound engine's maximum number of voices.

One key is missing, even when pressed alone

The issue is probably limited to that key, its connection, or the keyboard's MIDI configuration. Try the key in different parts of the keyboard and compare it with nearby keys. If it fails in the test every time, troubleshoot the controller before changing the lesson software.

Single notes work, but some chords lose notes

This can point to a limit in the keyboard's simultaneous input, a problem with a particular key combination, or a connection that is dropping messages. Test the same chord several times, then test different combinations with the same number of keys. If only one combination fails, note which keys are involved.

A note remains active after you release the key

The keyboard may not be sending a note release, or another input such as the sustain pedal may be keeping the note held. Repeat the test with the pedal disconnected or released. If the same note sticks without the pedal, check the key and connection.

The test receives nothing

The browser may not have access to MIDI, the wrong device may be selected, or the keyboard may not be connected in MIDI mode. Confirm that the test is open in a supported browser and that the keyboard appears as a MIDI input, not only as an audio device.

How to fix missed or stuck notes

1. Check the connection and power. Reconnect the USB cable at both ends and try another USB port. If the keyboard uses Bluetooth MIDI, confirm that it is connected as a MIDI device, not just paired for audio.
2. Close other music software. Quit digital audio workstations, virtual instruments, and other browser tabs that may already be using the keyboard. Then reload the test and select the device again.
3. Allow MIDI access in the browser. If you declined the access prompt, open the site's permissions from the icon beside the address bar, allow MIDI access if that option is available, and reload. If the permission is not offered, use Chrome or Edge on a computer rather than Safari.
4. Check the keyboard's connection settings. Some digital pianos can send MIDI through USB while using a separate setting for their internal sound. Consult the keyboard's manual for its USB-MIDI or computer connection mode. A setting called Local Control affects whether the keyboard plays its own sounds, and does not by itself prove whether MIDI notes are being sent.
5. Pair a Bluetooth keyboard again. On Windows 11, open Settings › Bluetooth & devices › Devices and check the connection. On macOS, open System Settings › Bluetooth. Remove and pair the keyboard again if it is disconnected, then reload the MIDI test.
6. Restart the browser and computer. This can release a MIDI device left open by another app. Reconnect the keyboard and test it before reopening your lesson software.

When the keyboard may need repair

If the same key repeatedly fails or sticks in the MIDI Test after you have tried another cable, another port, and a supported browser, the key or the keyboard's connection may be faulty. Test the keyboard on another computer if possible. If the problem follows the keyboard, contact the manufacturer or a repair shop, especially if it is still under warranty.

If every key and chord registers in the test but notes are missing only in one lesson app, the keyboard is probably sending the input correctly. Check the app's MIDI input choice, instrument, and any key-range or chord settings.

What polyphonic input means in this test

Polyphonic input means the keyboard can send several notes at once. Each key press and release is a separate MIDI event. The test helps you see whether those events arrive together, but it does not measure how many notes the piano's built-in sounds or a software instrument can play at once. Those are separate limits, so a successful MIDI check can coexist with a sound that cuts notes off in a particular instrument.