Delay time modulation effecting apparatus for processing musical tone

Abstract

A delay-time-modulation effecting apparatus employed by an electronic musical instrument or the like, is designed to effect a certain delay-time modulation on a musical tone signal so as to realize a desired modulation effect appear on a musical tone to be produced. The delay-time modulation is effected in response to a time lag between a write time and a read time at which the musical tone signal is written into and is read from a storage device (e.g., random-access memory). When a read address advances fast to be ahead of the write address, an overmodulation state emerges so that discontinuity in level of the musical tone signals occurs, which will result in an occurrence of noises. In order to avoid such an event, the read address should be limited not to advance ahead of the write address. Herein, the write address is generated in such a manner that the number thereof is circulatorily varied in a lapse of time within a certain address range, while the read address is generated by performing a computation using the modulation data and an offset address. The modulation data is generated in response to a desired modulation effect to be realized. The apparatus provides an address-limit circuit, which is activated when the overmodulation state is detected so that the read address is limited not to advance ahead of the write address. Thus, the occurrence of noises can be avoided.