Identifying formation layer tops while drilling a wellbore

Some systems and methods for determining depths of subterranean formation layer tops while drilling through the subterranean formation include a drill bit, a drill rig, a microphone, a depth sensor, and a processor. While drilling the through the subterranean formation, the processor receives a measured sound from the microphone and a measured drill bit depth from the depth sensor, normalizes the measured sound across all measured drill bit depths, determines frequency information of the normalized sound for each depth of the plurality of depths, determines frequency spectrums of the normalized sound for one or more depths of the plurality of depths, transforms the frequency spectrums into a depth spectrum, and determines the depths of subterranean formation layer tops based on the depth spectrum.