Wow thanks everyone for your responses! I generally have very little clue what is being said here (I have almost no experience in the world of electronics, I am a musician and sound engineer), and so I hope that someone might be willing to really spoonfeed me the steps involved in getting the parts and assembling whatever will work!
More details:
I am using a piano mic which has been designed to only pick up low frequencies (it will be blended in with other mics for the mid and high frequencies). On the mixer board, I will apply a low-pass filter to this mic, but I need to quickly reduce the signal level every time the pedal is released (it makes a slight thumping sound because all 88 dampers come slamming down on the strings to mute them). I figure that if I can use a "Y" patch cable right before the audio input on the mixer and sum together the mic and another signal containing a very loud 10kHz burst every time the pedal is released, I can use the compressor on the mixer board to act on itself pre-EQ, and I will set the threshold to above the maximum mic level, but below the burst level, and set it to last about 5ms. If the burst is 5ms long, and the compressor last for 5ms (attack of zero), the total compression time would be about 10ms which is the length of the thump on an oscilloscope.
So it seems my options here are to have a circuit design which sees a brief input voltage and outputs a brief 10kHz tone, or a circuit that outputs a brief 10kHz tone only when there is a voltage change from off to on. The first would require some kind of switch which can be flicked in either direction from a nominal position to which it returns, and the second would only require a simple push button. Yes?