A thin MEMS microphone can be used to detect audio levels and even perform basic FFT functions. You can read the analog voltage corresponding to the audio on analog pin #A4. Note that this is the raw analog audio waveform! When it's silent there will be a reading of ~330 and when loud the audio will read between 0 and 800 or so. Averaging and smoothing must be done to convert this to sound-pressure-level.
The microphone is sensitive to 100 Hz - 10,000 Hz audio frequencies. See the datasheet for more details.
You can read the raw analog value from the amplified microphone with
CircuitPlayground.soundSensor() this will give you just a value from between 0 and 1023 where the default 'quiet' voltage is ~330. At this time there is no function for automatic sound pressure level or frequency binning.