a tremolo effect producing system comprises at least one electro - acoustic transducer such as a loudspeaker for converting an electrical audio signal to a sound , at least one acousto - electrical transducer such as a microphone for converting sound to an electrical signal and disposed so as to face the loudspeaker , and at least one sound shielding member rotatably mounted between the above - mentioned two transducers and having sound transmitting openings or cutouts whereby sounds from the speaker will be periodically and / or individually interrupted with fade - in and fade - out effects as said member is rotated . these transducers and sound shielding member are sealed in a closed housing . thereby the sound wave emitted from the speaker through the openings or cutouts of the rotating member is converted to an electrical signal with natural tremolo effects by the microphone . the thus - produced signal may be mixed with an audio signal with non - tremolo effect and amplified and reproduced by a loudspeaker .