Noise Sensor uses a microphone with an amplifier to detect the sound level of the environment. It will capture the original sound wave, enlarge, and reproduce it in voltage form. When using the sensor to calculate the sound level, use the amplitude to decide the result.
 
Working Principle
The Noise Sensor is a combine of the microphone and amplifier, the microphone will capture the raw signal form the environment and let the amplifier chip lm386 to produce the amplified signal to the output.