High note priority monophonic brass keyer system

Abstract

A brass keyer system for an electronic organ wherein the keyboard is multiplexed to produce a polyphonic serial data stream, which is then converted to a monophonic serial data stream containing a keydown signal in a time slot corresponding to the highest note played on the keyboard. The monophonic data stream is converted to a multiple bit binary word that is used by the tone generation and keying portion of the system to produce a rectangular wave tone corresponding in frequency to the highest depressed key and having amplitude and pulse width modulation on attack and decay so as to produce a brass tone. The monophonic serial data stream is demultiplexed by means of a recirculating delay loop which repetitively recirculates the keydown pulse for the depressed key. The number of recirculations of this pulse are counted by a first counter and the position of the pulse within the delay loop is registered by a second counter, which is synchronized with the multiplexer. The outputs of the first counter form a first binary word representative of the octave of the highest depressed key, and the outputs of the second counter represent the pitch of the tone within that octave. Data selectors connected to the binary words select the appropriate pitch from the tone generator and the appropriate octave from the outputs of a divider so as to produce a single square wave tone of the proper frequency. Modified keydown pulses function as the amplitude and pulse width modulation envelopes, which impart to the square wave tone amplitude and pulse width modulation characteristic of brass tones. The octave select binary word is decoded and used to control the amount of differentiation of the square wave tone so that the pulse width modulation will track the position on the keyboard of the depressed key.