Acoustic signal generator with means for changing the time constant of the envelope signal

#The present invention relates to an acoustic signal synthesizer for synthesizing sound such as melody.

#This type of acoustic signal generator is disclosed in, for example, Japanese Laid-Open patent application No. 59-26789. When one sound is produced, its tone generally changes delicately as time elapses. Specifically, since high frequency components contained in the sound attenuate readily whereas low frequency components attenuate to a small extent, the condition (tone) of the sound changes delicately as time elapses. Therefore, according to the system disclosed in the foregoing application, three kinds of acoustic data are preset which correspond to the waveform of tone of a sound when it has just been produced, the waveform of tone when a certain time has elapsed after sound production so that the sound has attenuated correspondingly, and the waveform of tone when another certain time has elapsed so that the sound has correspondingly become more attenuated, these acoustic data are previously stored in three storage circuits (ROM) respectively. Then the waveforms of three sounds to be produced in succession are modified by the use of the three kinds of acoustic data, the resulting sound outputs are added digitally together, and the resulting output is converted from digital to analog form and modified by the use of one envelope signal; as a result, the three sounds are combined.

#In the foregoing system of combining three sounds by the use of one envelope signal, when the time constant of the envelope signal is large, attenuation is dull; thus, the strength of sound increases as the number of overlapping sounds increases. On the contrary, when the time constant of the envelope signal is small, the sound is attenuated quickly; accordingly, two or more sounds produced earlier become too weak to hear, making it difficult to discriminate the overlapping of sounds.

#FIG. 1 is a block diagram showing an embodiment of the present invention;

#FIG. 2 is a circuit diagram showing an example of a time constant circuit;

#FIG. 3 is a waveform diagram of several signals;

#In the block diagram of FIG. 1, storage circuits (ROM) 1, 2 and 3 are provided for, respectively, storing different acoustic data. Specifically, a plurality of different acoustic data corresponding to different sound sources, such as piano, violin, bell and the like are stored in these storage circuits. The number of storage circuits is identical to the number of sounds to be combined, e.g., three in the present embodiment.

#In conformity with the generation timing of each acoustic data, an envelope signal corresponding to each acoustic data is generated, and a time constant circuit 4 is provided for changing the time constant of each envelope signal in synchronism with the generation timing of each later generated acoustic data.

#A control circuit 5 supplies start signals P1, P2 and P3 and timing signals T1, T2 and T3 relating to the generation timing of each acoustic data to the time constant circuit 4.