Envelope generator

Abstract

An envelope generator comprises a counting circuit and counting control means capable of controlling a counting mode of the counting circuit, i.e., operation and non-operation of the counting circuit, counting speed, addition and subtraction etc., in accordance with an envelope shape to be obtained. There are various predetermined counting modes corresponding to different envelope shapes and the envelope generator includes selection means for causing the counting control means to select a desired one of the counting modes.

What is claimed is: 
     
       1. An envelope generator for an electronic musical instrument, said generator providing selectably different musical envelope shapes, comprising: a counting circuit selectively operable in a linear counting mode and in a non-linear counting mode, each in response to count pulses applied thereto;   a count mode control means for switching said counting circuit to one of said linear or non-linear counting modes;   a plurality of clock pulse sources, each supplying count pulses at different rates;   a count rate control means for applying to said counting circuit count pulses from a selected one of said sources;   an envelope shape selection means for programmatically causing (a) said count mode control means to select said counting modes and (b) said count rate control means to apply count pulses from different sources so that the resultant count values of said counting circuit will correspond to a selectable envelope shape; and   a conversion circuit for converting said resultant count values of said counting circuit to amplitude data;   said envelope generator thereby generating an envelope shape having an amplitude variation corresponding to the resultant variation in said count value.   
     
     
       2. An envelope generator as defined in claim 1 wherein said envelope shape selection means includes as one of its selectable envelope shapes a percussive damp mode in which said count mode control means and said count rate control means cooperate to cause said counting circuit to downcount gradually from a maximum count during depression of a key and, subsequently to release of the key, to cause said counting circuit to downcount quickly to a minimum count by applying count pulses of a faster rate to said counting circuit as compared with the rate of count pulses applied prior to release of the key; whereby said envelope generator generates an envelope shape which is provided with a short decay shape subsequently to release of the key.   
     
     
       3. An envelope generator as defined in claim 1 further comprising: envelope shape selection means for providing a set of binary coded signal respectively specifying different envelope shapes, said envelope shape selection means operating in response to said signals and to the actual count value of said counting circuit.   
     
     
       4. An envelope generator as defined in claim 3 wherein one of the envelope shapes specifiable by said signals is a direct keying mode in which the envelope becomes maximum value when a key included in said electronic musical instrument is depressed and becomes minimum value when said key is released, and wherein said envelope shape selection means includes circuitry for forcing the count value of said counting means to correspond to said maximum value in response to depression of said key and for forcing the count value to correspond to said minimum value when said key is released. 
     
     
       5. An envelope generator according to claim 3 wherein said instrument includes curve selection switch means for selecting a modified form of the envelope shape specified by said signals, said envelope shape selection means operating in response to actuation of said curve selection switch means to modify the programmatic selection of counting mode and the application of count pulses so as to cause the production of said modified form of selected envelope shape. 
     
     
       6. An envelope generator according to claim 1 wherein said conversion circuit includes a pair of voltage dividers connected between high voltage and low voltage sources, and corresponding two sets of gates respectively connecting points on said pair of dividers to a pair of output lines, said gates being operatively connected to said counting circuit so as to be enabled in accordance with the count value thereof, said envelope generator thereby producing on said pair of output lines two envelope shapes which vary symmetrically about a common voltage intermediate said high and low voltages. 
     
     
       7. An envelope generator for a keyboard electronic musical instrument, comprising: envelope mode selection logic means for providing a set of binary coded envelope mode selecting signals respectively specifying certain envelope shapes to be produced by said generator, .Iadd.   means for supplying count pulses, .Iaddend.   a counter operable to count in a linear manner and in an exponential manner in response to count pulses applied thereto,   count pulse rate selection means for controlling the rate of count pulses applied to said counter, and   envelope generation control logic means for programmatically controlling the manner of counting of said counter and the rate of count pulses applied to said counter in response to the depression and release of a key, to the provided envelope mode selecting signal and to the count value of said counter, so as to cause the count value of said counter to vary with time and to represent the amplitudes of an envelope having the shape specified by said provided envelope mode selecting signal.   
     
     
       8. An envelope generator according to claim 7 together with memory means comprising: a pair of voltage dividers connected between high voltage and low voltage sources, and   two corresponding sets of gates respectively connecting points on said pair of dividers to a pair of output lines, said gates being operatively connected to said counter so as to be enabled in accordance with the count value thereof, said envelope generator thereby producing on said pair of output lines two envelope shapes which vary symmetrically about a common voltage intermediate said high and low voltages.   
     
     
       9. An envelope generator according to claim 8 together with a musical tone waveshape memory having a voltage division circuit and a gate connected so as to sample selected points of said voltage division circuit at a rate which varies periodically according to the frequency of the tone associated with said depressed key, said pair of output lines from said memory means being connected to opposite ends of said voltage division circuit. .Iadd. 10. An envelope generator used in a keyboard electronic musical instrument for selectively generating an envelope waveshape signal which is used to impart a characteristic varying with time to a musical tone produced by said instrument, comprising: switch responsive means for producing a binary coded envelope selection signal indicative of a selected one of plural envelope waveshapes available for production by said envelope generator,   envelope mode selection logic for providing one subset of a set of envelope mode selecting signals in response to said binary coded envelope selection signal,   register means for storing envelope waveshape data corresponding to the current value of said envelope waveshape signal which establishes said time varying characteristic of the musical tone,   arithmetic means, receiving waveshape variation data, for arithmetically combining the waveshape variation data with at least a pair of said envelope waveshape data stored in said register means, the resultant new envelope waveshape data being stored in said register means in place of the data previously stored therein, said arithmetic means performing designatable arithmetic operations,   control logic means for programmatically controlling operations of said arithmetic means and producing said waveshape variation data in response to the depression and release of a keyboard key and to the provided subset of envelope mode selecting signals, said provided subset of envelope mode selecting signals at least designating the certain arithmetic operations of said arithmetic means required to obtain said selected one envelope waveshape, and   feedback means for feeding back at least a part of the stored envelope waveshape data of said register means to said control logic means so that the production of said waveshape variation data is modified thereby. .Iaddend. .Iadd. 11. An envelope generator according to claim 10 wherein said instrument includes curve selection switch means for selecting a modified form of the envelope shape specified by said signals, said envelope mode selection logic operating in response to actuation of said curve selection switch means to modify the programmatic control of said arithmetic means and the production of said waveshape variation data to cause the production of said modified form of selected envelope shape. .Iaddend. .Iadd. 12. An envelope generator as defined in claim 10 wherein said switch responsive means includes as one of its available envelope waveshapes a percussive damp mode in which said control logic means and said arithmetic means cooperate to cause said register means to count down at a first, relatively gradual rate from a maximum count during depression of a key and, subsequent to release of the key, to cause said register means to count down to a minimum count at a second rate that is relatively quicker than said first rate, thereby generating an envelope shape which is provided with a short decay shape subsequent to the release of the key. .Iaddend. .Iadd. 13. An envelope generator as defined in clim 10 wherein one of the envelope shapes specifiable by said signals is a direct keying mode in which the envelope becomes maximum value when a key included in said electronic musical instrument is depressed and becomes minimum value when said key is released, and wherein said envelope shape selection logic includes circuitry for forcing the count value of said counting means to correspond to said maximum value in response to depression of said key and for forcing the count value to correspond to said minimum value when said key is released. .Iadd. 14. An envelope generator used in a keyboard electronic musical instrument for selectively generating an envelope waveshape signal which is used to impart a characteristic varying with time to a musical tone produced by said instrument, comprising:   envelope mode selection logic means for providing a set of binary coded envelope mode selecting signals respectively specifying certain envelope shapes to be produced by said generator,   a source of count pulses,   a counter operable to count in selectable manners in response to said count pulses applied thereto,   count pulse rate selection means for controlling the rate of count pulses applied to said counter, and   envelope generation control logic means for programmatically controlling the manner of counting of said counter and the rate of count pulses applied to said counter in response to the depression and release of a key, to the provided envelope mode selecting signal and to the count value of said counter, so as to cause the count value of said counter to vary with time and to represent the amplitudes of an envelope having the shape specified by said provided envelope mode selecting signal, the resultant contents of said counter thus representing said envelope waveshape signal. .Iaddend. .Iadd. 15. An envelope generator used in a keyboard electronic musical instrument for selectively generating an envelope waveshape signal which is used to impart a characteristic varying with time to a musical tone produced by said instrument, comprising:   envelope mode selection logic means for providing a set of binary coded envelope mode selecting signals respectively specifying certain envelope shapes to be produced by said generator,   a source of count pulses,   a counter, operable in response to count pulses applied thereto, and having selectably different modes each characterized by a different net change in resultant count value per set number of applied pulses,   count pulse rate selection means for controlling the rate of count pulses applied to said counter, and   envelope generation control logic means for programmatically controlling the mode of counting of said counter and the rate of count pulses applied to said counter in response to the depression and release of a key, to the provided envelope mode selecting signal and to the count value of said counter, so as to cause the count value of said counter to vary with time and to represent the amplitudes of an envelope having the shape specified by said provided envelope mode selecting signal, the resultant contents of said counter thus representing said envelope waveshape signal. .Iaddend. .Iadd. 16. An envelope generator used in a keyboard electronic musical instrument for selectively generating an envelope waveshape signal which is used to impart a characteristic varying with time to a musical tone produced by said instrument, comprising:   envelope mode selection logic means for providing a set of binary coded envelope mode selecting signals respectively specifying certain envelope shapes to be produced by said generator,   means for supplying signals for incrementing or decrementing a counter by certain values,   a counter operable to count in selectable manners in response to increment or decrement value signals applied thereto,   rate selection means for controlling the rate at which said increment or decrement value signals are supplied to said counter, and   envelope generation control logic means for programmatically controlling the manner of counting of said counter and the rate at which said increment or decrement value signals are applied to said counter in response to the depression and release of a key, to the provided envelope mode selecting signal and to the count value of said counter, so as to cause the count value of said counter to vary with time and to represent the amplitudes of an envelope having the shape specified by said provided envelope mode selecting signal, the resultant contents of said counter thus representing said envelope waveshape signal. .Iaddend.