Adafruit Electret Microphone with Built-in Amplifier - Adafruit 1063, The Adafruit Electret Microphones with Adjustable Gain Amplifier feature a built-in microphone and use the MAX9814 microphone amplifier chip. There's a small trimmer pot on each one to adjust the gain between 25x and 125x so that you can minimise volume related distortion. They can be supplied with 2.4 to 5V DC and are capable of rail to rail output with a DC bias of Vcc/2. Be careful when selecting your power supply, 5Vpp may offend the Line Input of a standard amplifier for example. If you want to connect one to a Line Input then use a blocking capacitor of between 1 and 100µF unless you have a differential amplifier or it already has its own blocking capacitor. Adafruit recommend using a low-noise 3.3V DC supply if you intend connecting these amplifiers to an analogue to digital converter (ADC). In this application there's no need for a blocking capacitor. Adafruit have a tutorial and FFT library for the Arduino