Patent GB-1312161-A (GB)
Title: Electronical musical instruments
IPC: G10H7/04
Filed: 1971-05-24
Abstract: 1312161 Electrophonic musical instruments NORTH AMERICAN ROCKWELL CORP 24 May 1971 16593/71 Heading G5J  In an electrophonic musical instrument, keys, stops or like actuating members are scanned sequentially to provide a serial indication of which keys &c. are actuated to control the production of tone signals. Scanning the keyboards.-As described an electronic organ has four keyboards each with a maximum of eight octaves, with key contacts arranged in a 32 (octave) Î 12 (notes in an octave) matrix 11, Fig. 1. A counter 1 has three sections 2, 3 and 4 corresponding to the notes in an octave, octaves in a keyboard and keyboards respectively. The keyboard and octave counts are fed to an AND gate decoder 7 which sequentially addresses the octaves of key switches in matrix 11 and if one of the keys in an addressed octave is actuated the corresponding line 12 is marked. Lines 12 are sequentially sampled in an encoder 15 to produce a time division multiplexed (T.D.M.) signal with pulses in time slots corresponding to the actuated keys. Encoder 15 may comprise twelve AND gates, Fig. 3 (not shown), fed with the signals from counter section 2 and having outputs connected to an OR gate. Alternatively it is a parallel entry shift register emptied by the master clock signals, Fig. 3A (not shown). Tone generation.-Twelve tone generators are provided together with logic circuits, Figs. 7A and 7B (not shown) whereby when a key is operated it claims a tone generator until the key is released. Each tone generator comprises a read-only memory 103, Fig. 8, in which is digitally stored timed samples of a complex waveform. When a tone generator is claimed, a comparator 107 determines the instantaneous count on counter 1 to decide which note is to be produced. The sampling of memory 103 is at a constant frequency and unit 100 calculates or looks up in stored data the phase angles at which memory 103 is to be read to produce the required note. The samples from memory 103 are fed (via an accumulator 104 if they are recorded incrementally) to a digital to analogue converter and hence to an audio transducer. Voice stops.-The stop switches are arranged in an array 202, Fig. 12, which is sequentially scanned by a counter 200 in a fashion similar to that in which counter 1 scans the key switch matrix 11, the decoder 201 taking into account any coupling between voices set on couplers 209. A digital library of voices 204 is provided and when a particular voice is selected, the corresponding digital representation of the voice is assembled from the library in voices 207 and transferred into the register memory 208 and read out to the digital to analogue converter Fig. 8 to modify the tone signal-to produce the desired voice. Attack and decay.-The tone signals are subjected during attack and decay periods to sub-unity multipliers stored in read-only memory 125, Fig. 10. The multipliers are selected under the control of a counter 122 which counts up on actuation of a key and down on release. A monostable multivibrator 130 ensures that attack is completed in the event of premature key release. The frequency of counting and hence the speed of attack may be fixed by connecting switch 136 to the clock or made dependent on pitch by connecting to phase angle calculator 100. The maximum intensity controlled in response to the force with which the key is struck. Percussion.-Keying signals for conventional percussion generators are provided by feeding signals indicative of key depression and the multiplexed signal to separate AND gates the other input of which is fed from section 4 of counter 1, Fig. 11 (not shown). Reference has been directed by the Comptroller to Specification 1,245,678.