How to test sustain pedal polarity before resale

A sustain pedal that works backward can look broken, even when the pedal and keyboard are fine. If you are checking a used keyboard before buying or selling it, test the pedal’s response rather than relying on a quick press during setup.

The MIDI Test can show pedal input and MIDI messages from a keyboard or controller. Use it to check that pressing and releasing the pedal create distinct, repeatable changes.

Test the sustain pedal

1. Open the MIDI Test on a computer. Use Chrome or Edge if possible. MIDI Test does not work in Safari.
2. Connect the keyboard directly to the computer by USB, or connect its MIDI output through a MIDI interface. Plug the sustain pedal into the keyboard’s sustain or damper jack.
3. Allow MIDI access if the browser asks, then select the keyboard or controller if the test offers a device list. Follow the on-screen instructions to view its input.
4. With the pedal released, check the incoming messages. Press the pedal once, hold it for a moment, then release it. Repeat this several times while watching the pedal input or message list.
5. Try the pedal again after restarting the keyboard with the pedal plugged in. Some keyboards read pedal polarity when they power on, so the order of connection can affect the result.

Keep your hands off the keyboard keys during the pedal check. That makes it easier to tell which messages come from the pedal. If the test sees no input, make sure the keyboard is connected and selected before deciding that the pedal is faulty.

What the result means

The pedal turns sustain on when pressed and off when released

The pedal is behaving normally for a standard sustain setup. If you are buying the keyboard, this confirms that the computer receives pedal input, but it does not prove the pedal works with every keyboard or musical app.

Sustain is on while the pedal is up

The action is reversed. This is often a polarity mismatch, not a broken pedal. Look for a polarity switch on the pedal, or a pedal polarity option in the keyboard’s settings. Change one thing at a time, then repeat the press and release test.

Pressing works, but releasing does not

The keyboard may be receiving a pedal-on message without a clear pedal-off message. Check for a loose plug, a damaged cable, or a pedal that fails to return. If the MIDI messages appear inconsistent each time you repeat the test, treat that as a fault until another cable or pedal gives a reliable result.

No pedal input appears

The browser may not have access to the MIDI device, the wrong device may be selected, or the keyboard may not send the pedal input to its USB or MIDI output. Check the connection and test again. Silence in the message list alone does not identify which part is at fault.

How to fix reversed or missing pedal input

1. Check the pedal’s polarity switch. Some pedals have a small switch marked with two positions. Move it to the other position and test again. If there is no switch, check the keyboard’s manual or settings for a pedal polarity option.
2. Restart with the pedal connected. Unplug the pedal, turn off the keyboard, connect the pedal, and turn the keyboard back on. Some models detect the pedal’s resting position during startup.
3. Check the jack and plug. Confirm that the pedal is in the sustain or damper jack, not an expression or auxiliary jack. Push the connector in fully, and inspect it for bent or loose parts.
4. Reconnect the MIDI connection. Unplug and reconnect the USB cable or MIDI interface. Try a different USB port and avoid a hub for this first check. Close other music or MIDI apps that may be using the keyboard.
5. Compare with another pedal or keyboard. If available, test the pedal on a second compatible keyboard, then test a known-working pedal on the keyboard. This helps separate a pedal problem from a keyboard jack or setting problem.
6. Check browser access. If the test cannot see the keyboard, use a supported desktop browser and accept its MIDI access prompt if one appears. Reload the page after reconnecting the device. Safari is not supported by MIDI Test.

Windows 11 and macOS do not have a universal operating-system setting that changes sustain pedal polarity. The switch or setting is usually on the pedal or keyboard. On a Mac, Audio MIDI Setup can help you check whether MIDI devices are available to the system, but it does not correct a reversed pedal.

When the pedal or keyboard may be faulty

Suspect the pedal if it remains reversed after trying its polarity switch or the keyboard’s polarity option, or if presses and releases fail inconsistently on more than one compatible keyboard. A worn switch or damaged cable may cause intermittent messages. If you can, test a known-working pedal with the keyboard before making a purchase.

Suspect the keyboard if multiple compatible pedals fail in the same way, or if its sustain jack feels loose and input changes when the plug moves. Ask the seller to demonstrate the pedal and keyboard together, or arrange a repair inspection before paying. For a resale listing, describe any remaining problem plainly instead of calling an intermittent pedal fully working.

What the MIDI messages tell you

Many sustain pedals send MIDI Control Change 64, often shortened to CC64. In the standard MIDI convention, values from 64 to 127 mean sustain is on, and values from 0 to 63 mean it is off. The exact values may differ between devices, but the important check is that the state changes when you press and release the pedal.

A browser test can confirm the MIDI input it receives. It cannot inspect the pedal’s internal switch or guarantee that every music app will interpret the signal the same way. For a resale check, note the keyboard model, pedal model, connection used, and whether pressing and releasing changed the test’s input consistently.