Working in the field of soundscape ecology, a sub-category of ecoacoustics, Krause introduced a number of terms and concepts into the discipline to further define the sources of sound within the soundscape. They include geophony, the first sounds heard on earth consisting of non-biological natural sounds such as the effect of wind in trees or grasses, waves at the ocean or lakeshore, or movement of the earth. The second acoustic source is called biophony, the collective signature produced at one time by all sound-producing organisms in a given habitat. The third, and last of these elements is referred to as anthropophony, or human-generated acoustic signatures. In the final category, some sources represent controlled sound, such as music, theatre, or language. While a large percentage consists of incoherent or chaotic sound, referred to as noise. The first and last terms were implemented along with colleague, Stuart Gage, Professor Emeritus, Michigan State University.