Sustain pedal polarity: check it before a lesson

You press the sustain pedal and the notes stop ringing, or the sound stays sustained after you lift your foot. That can happen when the pedal's polarity does not match the keyboard's setting. Check the pedal before students arrive, so you can fix the setup instead of troubleshooting during the lesson.

The MIDI Test can show the messages your keyboard sends when you press and release its pedal. The pedal usually connects to the keyboard, and the keyboard sends the MIDI data to your computer.

Check the pedal before class

1. Open the MIDI Test in a browser other than Safari. Connect the keyboard to the computer, then allow MIDI access if the browser asks.
2. Make sure the keyboard is the MIDI input being monitored. If more than one device is listed, select or test the one connected to the pedal. The exact controls vary, so look for incoming MIDI messages rather than a named pedal button.
3. Keep your foot off the pedal, then press it once and release it. Watch for a message on controller number 64, also called sustain or damper. The test may show the controller number and value.
4. Repeat the press and release a few times. Check that the message changes each time and returns to the same released value after you lift your foot.

For a useful classroom check, play a few notes on the keyboard while testing. Confirm that the pedal sustains notes only while pressed, and that releasing it stops the sustain. The MIDI message tells you what the keyboard is sending, while listening tells you how the keyboard or instrument responds.

What the result means

The value changes when you press and release

This is the expected behavior. A common MIDI pattern is a sustain value of 127 when pressed and 0 when released. Other values can also be valid. The important point is that the pedal sends an on state when pressed and an off state when released.

The values work in reverse

If the keyboard sends an on state with your foot off the pedal and an off state when you press it, the pedal polarity is reversed for that keyboard. The pedal may still be fine. Check for a polarity switch on the pedal or a pedal polarity setting on the keyboard.

The value stays on after you release the pedal

The keyboard may not be registering the release. Check that the pedal is not stuck, the plug is seated, and the cable is not pulling the pedal out of position. If the message changes correctly but the instrument keeps sustaining, check the keyboard or instrument's sound settings instead.

No pedal message appears

The computer may not be receiving MIDI from the keyboard, or the keyboard may not send pedal messages in its current mode. Confirm that MIDI access was allowed, the correct input is selected, and the keyboard itself responds to the pedal. MIDI Test does not work in Safari, so a missing message there does not prove the pedal is faulty.

How to fix reversed sustain

1. Reconnect the pedal with your foot off it. Unplug the pedal from the keyboard, release it, and plug it in again. Some keyboards detect pedal polarity when they start, so switch the keyboard off before reconnecting, then turn it on with the pedal untouched.
2. Check the pedal for a polarity switch. Some pedals have a small switch marked polarity or a similar label. Turn the keyboard off before changing it, then restart and repeat the press-and-release test.
3. Look for a pedal setting on the keyboard. Open the keyboard's setup or controller settings and look for a setting named Pedal polarity, Damper polarity, or similar. Choose the option that makes sustain turn on when pressed and off when released. Menu names differ by model.
4. Check the connection to the computer. For USB, reconnect the keyboard directly to another port, if available. For Bluetooth, check the connection in Windows 11 under Settings › Bluetooth & devices › Devices, or on a Mac under System Settings › Bluetooth. Then check MIDI input again.
5. Restart the browser and keyboard. Close the MIDI test page, restart the keyboard, reopen the test, and allow MIDI access if prompted. This can clear a device connection that did not initialize correctly.

If you use a software instrument, check its own sustain behavior after the MIDI test reports the correct on and off messages. A keyboard can send the right data while an instrument's mapping or sound settings cause a different result.

When the pedal or cable may be faulty

Test the pedal on another compatible keyboard if one is available. If the pedal's message changes inconsistently, or does not change at all, try a different pedal in the same keyboard. This helps separate a pedal problem from a keyboard input problem. Avoid forcing a connector into a jack that does not fit, since pedal plugs and expression pedal jacks can look similar while serving different purposes.

If the same pedal fails on more than one compatible keyboard, inspect its cable and plug for damage. A pedal under warranty may be worth returning. For a low-cost pedal with a damaged cable or unreliable switch, replacement is usually more practical than repair.

Read the sustain value correctly

MIDI sustain uses controller 64. Values from 0 to 63 usually mean off, and values from 64 to 127 usually mean on. A keyboard may send values such as 0 and 127, or use other values on either side of that threshold. Do not assume the pedal is faulty just because its on value is not exactly 127.

For a classroom setup, test the actual keyboard and pedal combination students will use. A pedal that works correctly with one keyboard may have reversed polarity on another, so verify the behavior after swapping instruments or reconnecting equipment.