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Envelope Generation






MG-B Contour Generation




The MG-B project augments the existing Radio Shack MG-1 Concertmate synthesizer with six flexible envelope generators. < >The Envelope Generators drive;
  • The two VCA's that exist after waveform selection of each MGB VCO;
  • The MG-1 ladder VCF;
  • The SSM 2164 Low Pass Filter;
  • The two composite stereo output VCA's.
  • The two PWM inputs of the MGB VCO's
The envelope generators are "Virtual" in that each is a firmware routine that executes upon the microcontroller platform that also performs the MIDI to Control Voltage Conversion.

MGB MIDI Moderated Control DAC

The Control Voltages that drive the VCF are the composite result of individual routines that "sum" to binary values output to 16 bit DACS.  The DACs are scaled to allow the full range of the target circuit to be controlled.

MIDI parametric control of each Envelope generator is combined with an Ad Hoc front panel control.

Envelope Panel Interface

The MG-B User Interface is the combination of a Graphic LCD, six potentiometers, and 3 switches.  Four of the potentiometers are long throw slide controls and two are rotary controls.  The switches are simple momentaries.  The slide controls are parameter input controls used for the typical Attack, Decay, Sustain, Release parameter settings, but also are "re-used" for additional features such as Polarity, Amplitude, Delay, and Key Scaling.

Polarity selects the direction an envelope proceed in, low voltage to greater voltage or the inverse.  Amplitude sets the level of envelope excursion from no excursion to maximum possible setting.  Delay first selects whether the Gate and/or Trigger is delayed, and then by how much.  Keyscaling first selects whether the Attack/Decay/Sustain/Release are individually or all together impacted by the current assigned notes "numeric" value and then by "how much".

Usage of Contour Delay

The envelope generator allow the individual allocation of delay to the Gate and/or Trigger as each is the sum of a Trigger drive AD and a Gate drive AR software routines.  This allows a delayed gate AR to provide an initial "Blip" AD contour to "lead" the standard AR contour.  If the trigger alone is delayed this "blip" can locate within the AD attack cycle.  This delay can be Fixed, Keyscaled or Velocity driven.

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