To muffle jarring noise from a noise sound source and to give a tone color which is pleasant to a human ear by providing a tone color converter which receives the detection output of the noise and converts tone color and a second sound source generating means which receives the output of the converter and radiates converted sound waves.

The output of a noise detector 5 located in the vicinity of a noise sound source 2 is supplied to a tone color converter 24 and a second speaker 27. The converter 24 is used as a digital filter and its frequency characteristics is decided so that the output has 1/f characteristic of (-20dB/dec) when noise signals are inputted. Moreover, the converter 24 is constituted by a first order low pass filter which has a cutoff frequency of approximately 20 to 100Hz or a first order integrator, when the frequency spectrum of the source 2 is approximately the same level from low to high frequencies, i.e., white noise. When the low frequency components are less and the high frequency components are much, the digital filter is constituted so as to have frequency spectrum to increase the low frequencies and to attenuate the high frequency components.