My final project is real-time vocal tuner built with the Adafruit ESP32 Feather and a Sparkfun microphone. Its main charge is transforming incoming audio input (in volts) into a frequency in Hertz. I created a server on the Feather (Huzzah?) that sends the frequencies to my laptop, where the values are updated every second. This is visualized in a javascript gauge animation as well as some pithy remarks in response to your singing. Check out the video here!