Noise suppression is performed based on null coherence between sub-band signals of a primary acoustic signal and a secondary acoustic signal. The null coherence of a signal refers to portions of the signal that have high coherence and can be nullified by a null processor. The nullified component corresponds to target sources, such as an individual speaking into a phone. The coherence values indicate the presence of a target source and are used to suppress noise in portions of a signal that are not dominated by a desired target source. The inter-microphone level difference may be used in combination with the null coherence to provide noise suppression.