In this paper, a method for evaluating the cleanness of each time-frequency bin of multichannel spectrograms is proposed. When observing acoustical signals with noise and/or interference, the degree of noisiness is usually different for each bin in the time-frequency domain. Therefore, array signal processing techniques should be possible to be improved by choosing only “cleaner” bins, which contain less noise and/or interference, for extracting the spatial information. The proposed method aims to distinguish such clean bins from noisy ones. To do so, the similarity of phase derivative among channels is considered since phase is sensitive to noise and interference. Constant phase is removed by derivative so that convolutive mixtures can be handled without care on spatial condition. The proposed method is applied to direction-of-arrival estimation (MUSIC method) and blind source separation (independent vector analysis) for demonstrating the possibility of the proposed measure.