LOW FREQUENCY MODULATION CIRCUIT FOR MUSICAL SOUND GENERATOR

摘要

PURPOSE: To improve accuracy and stability by changing the frequency division ratio of a frequency counter for determining the reading frequency of an waveform data memory by the digital operation of data from a frequency register and data from a modulation memory. CONSTITUTION: When an arithmetic circuit 5 is an addition (subtraction) circuit, data for one word are read out from the modulation memory 8, added to the data of the frequency register 7 and the added result is inputted to the frequency counter 2 to determine the frequency division ratio of an oscillation clock 1. At the time of reading out the data of a succeeding address from the memory 8, the read data are added to the data of the register 7 again to change the frequency division ratio of the counter 2. Namely the reading frequency of the memory 3 is successively changed in each reading of data from the memory 8, so that the change of the frequency appears as a modulation effect. Consequently the accuracy and stability of the circuit can be improved.