A series of experiments was conducted concerning the loudness and timbre of broad bandnoise mixed with frequency-modulated sounds. The results suggested the follow ings:(1) FM sounds overlapped on broad-band noise can be just detectable when S/N is around zero (S: the level of FM sound, N: the 1/3 octave band level of broad-band noise with center frequency corresponding to carrier frequency of FM sound).(2) FM sounds overlapped on broad-band noise can be detected at S/N of-10 dB or less when it is interrupted.(3) The loudness of broad-band noise shows good correspondence with Leq. However, when a prominent frequency component, such as FM sounds, is included, loudness level based on ISO 532B (LLz) shows better correspondence than Leq.(4) The timbre becomes deteriorated when the level of specific frequency component in creasesor when its frequency becomes high. These effects were found even when the overall values of Leq were kept constant. Neither Leq nor LLz is sufficient for evaluating these effects. The method for calculating sharpness proposed by von Bismarck is an ap propriatemethod for evaluating the metallic aspect of the timbre.