GB1405238A - Integrated circuit all-harmonic wave organ system including provision for flute tones and pedal notes - Google Patents

Abstract

1405238 Electronic musical instrument HAMMOND CORP 9 March 1973 [28 April 1972] 11650/73 Heading G5J In an electronic organ, tones are synthesized from harmonics extracted from staircase waves, themselves constructed by the addition of square waves at the fundamental frequency and in decreasing proportions at the next three higher octaves, waves above the eighth octave being omitted. Flute tones may be extracted by filters from the fundamental square waves, but if the filters are to handle a complete octave, the second harmonics must not be present in the inputs. This is true of a square wave but not of the staircase wave, but to save connection pins on a large-scale integrated circuit it is desirable to use the staircase wave for all purposes, the problem being overcome by gating out the first octave square wave making up the staircase when flute tones are required. Circuits for two adjacent semitones (e.g. C, C#) in all octaves are mounted on one chip: square wave source 100 provides eighth octave high frequency input for note C, with octave dividers 106, 110-130 down to first octave, and clearing bus 134 for initial phasing of the dividers. Keying blocks 140 combine four square waves from the dividers to form a staircase wave, under the overall proportional control of keying and envelope shaping units supplying voltage to terminals 162. The descending amplitudes of the higher components of the staircase are obtained by selection of impedance of the appropriate MOSFET. When flute tones are to be filtered from the output, gates 170 are blocked by control 172 to inhibit first octave component from the staircase wave. Four-component staircase outputs with fundamentals in octaves up to the eighth, with two adjacent semitones in common, are available at terminals 176, 178-188, components above eighth octave being omitted. Other keying blocks with similar gates on the same chip are assembled into units corresponding to 16, 8 and 4 foot pedal registers for the lowest three octaves 200, 210, 212. Pipe tones are then produced by formanting circuits outside the scope of the invention. Outputs from all key blocks serving registers of the same footage for the two adjacent semitones are commoned 204, 206, 208, while each octave has its own key and envelope control terminal 202 for each note.