A musical tone synthesizing apparatus at least comprises two loop circuits. Each loop circuit delays an input signal thereof by a delay time corresponding to a tone-pitch period of a musical tone to be produced while circulating the input signal therethrough. When the loop circuits are connected in series, an excitation signal is applied to one loop circuit, while an output signal of one loop circuit is supplied to another loop circuit. Then, the excitation signal is mixed together with the output signals of the loop circuits, so that a musical tone signal representing a synthesized musical tone is generated. The excitation signal is generated by mixing a noise signal and a musical-tone-waveform signal. When simulating the violin sounds, the noise signal is made based on a frictional sound which is caused due to a friction between a string and a bow. Incidentally, a filter can be provided to perform a filtering operation on each of the excitation signal and the output signals of the loop circuits. Further, an overflow detecting circuit can be provided to detect an overflow event in which a signal level of the signal circulating through each loop circuit exceeds a predetermined limit value representing the maximum value of the digital data, used in the apparatus, whose number of bits is determined in advance. When the overflow event is detected, an input level of each loop circuit is automatically adjusted. incidentally, the signal level can be visually indicated by indicators such as LEDs.