Sustain pedal polarity: how to test your setup

Your sustain pedal may hold notes when you lift your foot, or stop sustaining when you press it. That can happen when the pedal's polarity does not match the keyboard or MIDI controller. Polarity describes whether the pedal reports an on or off state while pressed or released.

You can check what the pedal is sending before changing your studio setup. The MIDI Test shows incoming MIDI messages, including pedal data, so you can compare the pedal's released and pressed states.

Test the pedal's polarity

1. Open the MIDI Test in a browser with Web MIDI support. The test does not work in Safari. Connect your keyboard or MIDI controller and allow MIDI access if your browser asks.
2. Choose the connected device if the test offers a device list. Keep the sustain pedal connected to the keyboard or controller, not directly to the computer unless it is a USB MIDI pedal.
3. Leave the pedal up and watch the incoming messages. Note the pedal message or value that appears while it is released.
4. Press the pedal fully and watch again. A typical switch pedal sends sustain off when released and sustain on when pressed. For MIDI Control Change 64, values below 64 are generally off, while values of 64 or higher are on.
5. Release and press it several times. The released state should be consistent each time, and the pressed state should be different. If the values seem inverted, check the fixes below.

Some pedals send a continuous range rather than a simple on or off message. That can be normal for a half-damper pedal, which lets compatible instruments respond to how far you press. If the values move gradually as you press, compare them with the keyboard or instrument's pedal settings instead of treating every value as a polarity fault.

What the result means

The value changes from off when released to on when pressed

The pedal is sending the expected direction. If notes still sustain at the wrong time, the keyboard, controller, or instrument may have a different pedal assignment or may be interpreting the message incorrectly. Test the pedal's sound in another instrument or setup before changing its polarity.

The value is on when released and off when pressed

The pedal's polarity is likely opposite to what the keyboard expects. Look for a polarity switch on the pedal or a sustain polarity setting on the keyboard. Many keyboards also detect polarity when they start up, so the pedal's position during startup can matter.

No pedal message appears

The browser may not have access to the MIDI device, the wrong device may be selected, or the pedal may be plugged into the wrong jack. The MIDI controller connected but software sees nothing guide can help if the device itself is missing from the test.

Values change unpredictably or only at certain angles

This points more toward a loose plug, damaged cable, or worn pedal switch than a polarity mismatch. Polarity usually reverses the relationship between pressed and released states; it does not normally make the signal intermittent.

How to fix it

1. Check the pedal's polarity switch. Some pedals have a small switch marked with polarity symbols or labels such as POLARITY. Try the other position, then repeat the MIDI test. Do not force a switch that is not meant to move easily.
2. Plug into the sustain jack. Check that the pedal is connected to the keyboard's Sustain or Damper input, not an expression or assignable jack. If the labels are unclear, check the keyboard manual before changing connections.
3. Restart with the pedal released. Turn off the keyboard or controller, make sure the pedal is plugged in and fully released, then turn the device on. Some models read the pedal's state during startup and use it as their polarity reference.
4. Look for a pedal setting on the instrument. Check the keyboard or controller's settings for sustain polarity, pedal type, or damper assignment. The name and location vary by model. Change one setting at a time and test again.
5. Reseat the connection. Disconnect and firmly reconnect the pedal plug. If it uses a removable cable, try another compatible cable. Avoid twisting or pulling the cable while the plug is inserted.
6. Test another pedal or device. If possible, connect the pedal to another compatible keyboard, or test a known working pedal on your keyboard. This separates a pedal fault from a keyboard input or configuration problem.

If you are using a computer, the browser must support Web MIDI and have permission to access the controller. If the device does not appear in the test, try a supported browser such as Chrome or Edge on a computer. A browser MIDI test can show the messages reaching the computer, but it cannot change a pedal's wiring or prove that a particular instrument will respond correctly.

When the pedal may be faulty

If the pedal sends no message on more than one compatible device, check its cable and plug for visible damage. If the message cuts in and out when the pedal moves, or the values jump without a deliberate press, the switch or cable may be worn. A pedal under warranty is a good candidate for replacement or service. For an inexpensive pedal, replacing it is often more practical than repairing the internal switch.

Polarity is not the same as pedal type

A basic sustain pedal works like a switch. It is either pressed or released. Polarity determines which state the device treats as sustain on. A half-damper pedal instead sends changing values over part of its travel, allowing a compatible instrument to respond to partial pedal movement. Reversing polarity cannot make a basic switch pedal behave like a half-damper pedal, and a half-damper pedal may not work as intended on a keyboard that supports only on and off.

Use the same pedal position and the same connected device when comparing readings, because changing the device's startup position can affect automatic polarity detection.