Why a MIDI keyboard sends Note On with zero velocity

Your MIDI monitor shows a Note On message with velocity 0, and it looks as if your keyboard is sending the wrong signal. In many cases, it is not a fault. MIDI devices commonly use a zero-velocity Note On to mean that a key has been released.

Use the MIDI Test to watch the messages from your keyboard as you press and release keys. The timing of the message is the key to telling a normal release from a problem.

Check the MIDI messages

1. Open the MIDI Test in a current browser on a computer. It does not work in Safari. Connect your MIDI keyboard, and allow MIDI access if the browser asks.
2. Find your keyboard in the available MIDI device list, if there is more than one device.
3. Press one key slowly, hold it for a moment, then release it. Watch the messages and the velocity readings for the full press and release.
4. Repeat with a few other keys. Press each key firmly enough to register, and avoid playing a chord while you are checking one message at a time.
5. If you have another MIDI keyboard or controller, connect it and repeat the same test. Comparing devices can show whether the issue follows the keyboard or the computer.

What the result means

Note On with velocity 0 appears when you release a key

This is usually normal. MIDI uses Note On with a velocity greater than 0 to start a note. A Note On with velocity 0 is conventionally treated as a note release, much like a Note Off message. Some keyboards and software use this form because it can be sent efficiently.

Check the order of events. When you press a key, you should see a Note On with a velocity above 0. When you release it, you may see either a Note Off or a Note On with velocity 0. If that is what happens, the zero is not the velocity of the note you played.

Velocity 0 appears as soon as you press the key

That is not the usual pattern for a playable key press. The receiving software may interpret it as a release, so it may not start a note. Repeat the test with a different key and device, if available. If the same keyboard sends zero on every press, check its settings and connection.

Some keys send a velocity above 0, but others do not

A pattern limited to particular keys can point to a key sensor or contact problem. Test each key slowly and separately. If one key repeatedly sends a zero-velocity message on press while neighboring keys work, the issue may be inside the keyboard.

There is no message when you press or release a key

The computer or browser may not be receiving data from the keyboard. Check that the correct MIDI device is selected, that the browser has access, and that the keyboard is connected and powered. The MIDI Test checks incoming MIDI messages. It does not prove that a sound-producing app is set up correctly.

How to fix unexpected zero-velocity messages

1. Check whether the zero is a release. Press one key, wait, then release it while watching the message list. If the zero appears only after a nonzero Note On, the keyboard is likely behaving normally.
2. Check the keyboard's settings. Look for a velocity curve, fixed velocity, or MIDI transmit setting in the keyboard's own controls or its manual. A fixed-velocity setting should still send a nonzero value for a key press, so compare the message when pressing and releasing.
3. Reconnect the keyboard. Unplug and reconnect a USB keyboard, or disconnect and pair a Bluetooth MIDI device again. Try another USB port and connect directly to the computer instead of through a hub.
4. Check that the computer sees the device. In Windows 11, open Start › Device Manager and check the relevant entries under Sound, video and game controllers or Universal Serial Bus controllers. On macOS, open Applications › Utilities › Audio MIDI Setup and check whether the MIDI device appears.
5. Allow access in the browser. If the browser shows a MIDI permission request, allow access for the test page. Reload the page and select the device again. If access is blocked, check the site's permission in the browser's address bar settings.
6. Restart the keyboard and computer. Power-cycle the keyboard, then restart the computer if the device still fails to appear or send messages. This can clear a connection that stopped responding.

Why a zero-velocity Note On is useful

A MIDI message includes a type, a channel, a note number, and a velocity value. Velocity usually describes how quickly or forcefully a key was pressed, though the keyboard and receiving instrument determine how that value affects the sound. MIDI devices can mark a key release with a Note Off message or use a Note On message with velocity 0 instead.

So do not judge the message by its name alone. Look at what happened just before it. A zero-velocity event after a normal Note On is usually the end of the note. The same event at the moment you press a key, especially if it repeats across keys, is worth investigating.

The MIDI Test shows messages from the connected controller, but it cannot tell you whether a particular music app is interpreting them correctly.