Electronic musical instrument having filter-and-delay loop for tone production

An electronic musical instrument comprising:

• a waveshape memory storing digital words of N number, these digital words representing the amplitudes at N sample points of a certain waveshape, respectively;
• means for generating a clock pulse of a selectable frequency, said digital words being read out, one after another, from said waveshape memory for each arrival of said clock pulse;
• a selector having a first and a second input terminal and an output terminal which is selectively connectable to either said first input terminal or said second input terminal;
• a filter having an input terminal connected to said output terminal of said selector, and an output terminal;
• a counter for counting said clock pulse to deliver a switch-over signal to said selector when said digital words of N number are all read out from said waveshape memory,
• said selector being operative so that it makes a connection between its output terminal and its first input terminal in the absence of said switch-over signal and that it makes a connection between its output terminal and its second terminal in the presence of said switch-over signal;
• and
• an N-stage shift register having an input terminal connected to said output terminal of said filter and an output terminal connected to said second input terminal of said selector,
• the shift register being operative so that the contents of the respective stages of this shift register are shifted one position towards the output terminal thereof for each arrival of said clock pulse;
• there being obtained at said output terminal of said selector an aimed musical waveshape in digital representation.

In an electronic musical instrument of the type comprising a waveshape generator for providing a signal indicative of at least one period of a predetermined waveform, and a recirculating loop receptive of said waveform signal for modifying said waveform to provide an output signal, said output signal being provided at an output terminal and representative of a musical tone, the improvement wherein:

• said loop comprises a filter of predetermined transfer function operating upon said output signal;
• a delay circuit, interposed between said filter and said output terminal, said delay circuit providing a delay in accordance with said waveform period such that each successive cycle of said output signal is indicative of said predetermined waveform operated upon by said transfer function a respective increasing number of times;
• and
• a selector for initially coupling said waveform signal directly to said output terminal for the first period of said output signal such that the first cycle of said output signal is determined by said predetermined waveform, and thereafter decoupling said waveshape generator from said output signal such that said output signal is generated by said delay means.