The base concept of an audio visualizer is: an output reacts to a change in an input. This base interaction was what originally inspired the idea. In this case, a device, the Sparkfun sound detector board, is measuring the change in the environmental noise level through the principle of capacitance. Team 8 was interested in understanding the fundamentals of how microphones functioned and how easily it could drive an output such as a strip of LEDs.
The Sparkfun sound detector works off of two main theories, the first being the theory of parallel plate capacitance. This theory essentially states the closer the two plates are the lower the capacitance. For a standard parallel plate capacitor, the voltage is inversely proportional to the capacitance as modeled by the equation Q = C*V. Q is the amount of charge that moves across the two plates, while c is the capacitance in farads and V is the potential difference. In the case of the microphone, the voltage was set at 3.3V. The voltage that comes out of this tiny parallel plate capacitor is very small. This is where the second principle of op-amps comes in. The op-amp circuit shown above is used to amplify the voltage from the microphone to the rest of the circuit. In our case team 8 used analog port 0 to read the value from the envelope output pin and analog port 2 to read the values from the audio pin.
The figure above shows the two outputs used by team 8: envelope and audio. These outputs controlled the number of LEDs to be lit up. This interpolated relationship is how the LED visualizer works. The team would take the envelope signal map to a value from 0 to 9 then iterate a for loop to illuminate that mapped number of LEDs. The LED would utilize an RGB implementation to understand which color it was going to display.