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How to test MIDI message filtering on a web page

Compare what a MIDI controller sends with what a web page receives, so you can tell whether messages are missing, blocked, or filtered.

Michael ReedHardware tests Tests 4 min read

A key, knob, or pedal works in one web app but seems ignored in another. The app may be filtering that kind of MIDI message, or the controller may not be sending it at all.

Compare the controller's output in the MIDI Test with what the page in question receives. This helps you narrow down whether the issue is the controller, browser access, or a filter in the page.

Compare the messages

  1. Open the MIDI Test in Chrome or Edge on a computer. The MIDI Test does not work in Safari.
  2. Allow the browser to access MIDI devices if it asks. Connect or select your controller if the test offers a device list.
  3. Try one control at a time. Press and release one key, turn one knob, and press and release a pedal. Check whether the test shows a message for each action.
  4. Open the web page you are troubleshooting and grant it MIDI access too. Repeat the same actions, one at a time, and check which ones the page responds to.
  5. Compare the two results. If the test shows a message but the other page does not respond to the same action, check that page's input, channel, and message-type filters.

Use the same controller and controls for both checks. A knob may send a different kind of message from a key, and a pedal may send nothing until you press or release it. Make each movement clearly, then wait a moment for the page to update.

What the result means

The MIDI Test shows messages, but the other page ignores them

The controller and browser can deliver those messages to a web page. The other page may be listening to a different device, channel, or message type, or it may be set to ignore that control. Look for input or mapping options in that page, and check whether a filter is enabled.

Neither page shows a message for one control

The controller may not send a message for that action, or it may be in a mode that changes what its controls transmit. Not every MIDI controller sends every message type. Check the controller's manual or configuration software to confirm what the control is supposed to send.

The test shows keys but not knobs or pedals

The keyboard part is reaching the browser, but the other controls may use a different message type or may not be configured to send MIDI. Many knobs and pedals send Control Change messages, while keys commonly send note messages. Test another knob or pedal before concluding that the page filters all controls.

No messages appear anywhere

The browser may not have permission, may not support the feature, or may not see the connected device. Confirm that you are using Chrome or Edge on a computer, then check access and the connection using the fixes below.

How to fix it

  1. Check the page's input selection. If it has a MIDI input menu, choose the controller you are testing. Some devices have multiple ports with similar names, so try each listed input.
  2. Review filters and mappings. In the page that misses messages, check for options that restrict input by channel, device, control, or message type. Disable a filter temporarily, or map the control again, then repeat the same test.
  3. Allow MIDI access. Accept the browser's permission prompt for the page. If you previously blocked access, open the site controls beside the address bar, review the page's permissions, allow MIDI access if that option is listed, and reload the page. A work or school browser policy may prevent you from changing this permission.
  4. Use a supported browser. MIDI Test does not work in Safari. Try Chrome or Edge on a computer, and make sure the browser is up to date. The web page you are testing may have its own browser requirements.
  5. Close other music software. Quit digital audio workstations, MIDI utilities, and other browser pages using the controller. Reopen the test page and check whether the device appears. Another program or page can sometimes affect which device is available.
  6. Reconnect the controller. Unplug and reconnect a USB controller, or disconnect and reconnect a wireless one. If possible, try another USB port and connect directly rather than through a hub.
  7. Restart the browser, then the computer. Close the browser completely and open it again. If the controller still does not appear, restart the computer and test before opening other music software.

What a web test can confirm

A browser test can show messages that the connected controller and browser make available to the page. It cannot inspect a filter hidden inside another website, prove what a music program received, or tell you why a controller chose not to send a message. That is why comparing the same action in two pages is useful: the MIDI Test is a reference, not a view into the other page's settings.

A MIDI message is a small instruction such as a note press, a knob value, or a pedal change. A page can listen for some kinds and ignore others. If the MIDI Test displays the message but the target page does not react, focus on that page's device selection and filters. If neither page receives it, check the controller's mode, connection, and configuration first.

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