Sustain pedal changing polarity and back - mystery

Hi all,

I had a strange (and very stressful) issue performing at Brighton Fringe last week: from one show to another, my sustain pedal changed polarity. Not the hardware - I had 2 pedals, swapped one for the other and no difference - but in Cantabile. We only had 15m between shows, which is minimal for clearing stage of previous gig, setting up and sound checking, so I detect my sustain is reversed, switch pedals, fiddle about, then remember there is a Cantabile filter to do undo that, go online, look up how to fix the issue etc etc. We actually missed 10m of our 1hr slot.

And very strange - the day after the behavior was back to what it was before - undid the filter and all was well.

What I don’t understand is why. Nothing changed between gigs. Same hardware, same software. Just one day sustain behavior reversed and day after it reversed again.

Anybody any clue as to what my have caused this? So far the issue has not reproduced itself …

Just a hunch: some keyboards detect the state of switch pedals connected on startup and auto-configure themselves accordingly: if the switch is closed on startup, they assume it is a “breaker” setup, if it’s open, it is a “closer” setup. With these keyboards, if you accidentally have the pedal pressed while the keyboard is starting up, it will get confused and configure your pedal in the wrong way.

Only solution to this: restart the keyboard making sure that the pedal is not pressed.

Easy to test if your keyboard is doing this - just switch the keyboard on while having the sustain pedal pressed and see what happens…

That is a great hint! I’ll test it!

Though I would say that if this is the cause, I’m pretty sure I have done both before - keybd on before / after I plug in the sustain pedal …

I’ll report back!


I have experienced Torsten’s observation. I would add that one time I didn’t have the pedal jack completely inserted and as such the polarity was incorrectly ‘guessed’ by the MAudio keyboard. Inserting the connector completely did not fix the problem, I also needed to power on/off the keyboard so it could re-detect.

Plugging in before or after boot-up may not be the issue in these cases. The problem is having the pedal pressed when booting up the keyboard. The keyboard will detect the state of the switch when booting up and declare that as “pedal up”. Now once the state changes, it will recognize a “pedal down”.

Technical note: with '“switching” sustain pedals it’s not about “polarity” (how the wires are connected, as is typical for expression pedals), but about “switching behavior” - these pedals are just a simple circuit breaker, so one wire goes in, the other out, and if you change the polarity, this will not affect functionality. So the difference between pedals is if they are a “closer” type (closes the connection when pressing) or “breaker” type (breaks the connection when pressing). Different keyboards manufacturers use different switching behaviors; there are pedals that allow you to change switching behavior (not “polarity”) with a little slider at the bottom to adapt to these different keyboards. And some keyboard manufacturers try to be smart and detect the type of pedal that is attached by the state of the switch when they boot up - and that could be the problem.

So if you have a typical “closer” switch attached, the circuit will be “open” when the pedal is up and “closed” when it is pressed. When you press it during the boot-up process of the keyboard, it will recognize that the circuit is closed, and try to be smart: “oh, someone connected a ‘breaker’-type pedal - so I will treat it as such and wait for the circuit to be ‘open’ and recognize that as a pedal-press”.

So it’s not about having the pedal connected or not, but it’s about fooling the keyboard into recognizing it as the wrong type during boot-up.



This is very easy to explain: two scenarios:

  • when you don’t fully insert the plug of a “closing” pedal, the tip of the plug may accidentally create an electrical bridge between the tip and the ring contact of the socket. So the keyboard will recognize the pedal as “breaking” (because the circuit was closed on boot-up). Once you push the plug in fully, the connection breaks (closing pedal is open at rest), which the keyboard thinks is “pressed”
  • or if the plug of a “breaking” pedal stays further out of the socket, the tip will not reach the “tip” contact, so the connection will stay open during boot-up - “closing” pedal recognized. Once you push the plug fully in, the connection will be closed - keyboard thinks that pedal is pressed.

So yes, incorrectly plugging in the pedal (and correcting after) can also confuse your keyboard - only remedy is to reboot.