Analogue Systems RS-510e EMS Trapezoid Generator Eurorack Module

Genuine Ems trapezoid generator featuring Attack, On, Decay, Off and Trapezoid output level. With v.c of Decay time, status led, Sig in and Sig out, Gate in and Outputs A and B this classic timing generator when used with RS-500e captures the essence of the VCS3 and Synthi A. This module is made under license from EMS.

The combined contour generator and VCA used in the EMS VCS3 and various Synthis (the "Shaper") is a very clever piece of electronic design, and it allows you to create sounds and effects that are all but impossible on more conventional synthesizers.

The RS-510e incorporates both elements of the VCS3 Shaper, comprising two modules that would often be found as separate modules. The first of these is the envelope generator itself, referred to as the Trapezoid Generator. The second is a VCA. We will deal with each of these in turn.

The Background to the Trapezoid

The Trapezoid Generator was perhaps the most confusing module within the VCS3 and Synthis, largely because it acted in an unusual way that was not intuitive to users of other manufacturers' instruments. In retrospect, it's hardly surprising that players considered it arcane and impenetrable, but this is unfortunate, because it is a flexible and powerful tool.

To understand how the Trapezoid Generator differs from conventional contour generators, let's first consider the common ADSR envelope.

This has four stages, as follows:

A: The Attack stage determines the speed at which the voltage achieves its full value.

D: The Decay determines the speed at which the voltage drops until it reaches...

S: The Sustain Level, the level the voltage maintains while a Gate is detected, and ...

R: The Release, which determines the speed at which the envelope voltage decays back to zero after the Gate is released.

(For more information about the standard ADSR envelope generator please refer to Appendix 3.)

The Synthi Trapezoid also comprises four stages, but these are called Attack, On, Decay, and Off. It works as follows:

Manual operation (Contour Generator):

A: When a Gate is detected, the contour enters its Attack phase, like a conventional ADSR. If the Gate is very brief (a trigger)the Attack is completed nonetheless, and the contour moves to the next stage...

ON: After the Attack, the contour is "ON", and maintains its maximum voltage for as long as the Gate is present. Once the Gate is removed the contour remains ON for an additional time determined by the ON control.

D: At the end of the ON period, the contour decays to zero.

Free running operation (LFO):

A: From its initial state, the contour enters its Attack phase.

ON: After the Attack, the contour is "ON" for a time determined by the ON control.

D: At the end of the ON period, the contour decays to zero.

OFF: Once the decay is complete, the contour remains at zero (i.e. "OFF") for a period determined by the OFF control, and then enters the Attack phase again.