In order to apply engineering controls to a noise source it must first be identified. This can be a problem in the power plant environment where a source may dominate in one band and not in others. The problem is complicated by the directivity of the various sources such as fans, ducts, and machinery. A technique of generating sound level contours using relatively large numbers of measurement locations has been developed and aids in source identification. Using a high speed computer to display the sound levels in each frequency band allows the engineer to pinpoint the dominant sources and their frequency. The method is suitable for octave, third‐octave or narrower bands; several examples are given. Extensions including automation using computer controlled graphics are also discussed.