Hello arduino community. I currently have an arduino with a piezo element attached to it, which is able to convert
an analog signal to digital, and output the println "knock". However, i am so curious to know if it is possible
to output the frequency value of the knock in the program, or more importantly, is it possible to just read in knocks of a certain
frequency range. I am aiming to read in the vibration of a table tennis ball on a table, while ignoring the vibrations
caused by someone putting their hand on the table, for example. Thanks 
I've been looking at using a condenser microphone and and amplifier, so i can read in quieter vibrations, any help on this would be much appreciated
I would work with the piezo/mic output before the Arduino. Use something like a limiter or compressor to tweak the sound. The way these sensors are connecting to Arduino allow to register volume/velocity only.