rs510e ems synthi trapezoid generator
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1. CK LED The red LED gives you a direct visual indication of the voltage being produced by the trapezoid When the LED is extinguished the trapezoid is OFF As the LED becomes brighter the trapezoid is passing through the Attack phase When the LED is at its brightest the trapezoid is ON As the LED dims the trapezoid is passing through its Decay Remember that a bright LED does not necessarily imply a ve output voltage because the trapezoid can be inverted using the OUTPUT LEVEL CONTROL ANALOGUE SYSTEMS RS INTEGRATOR 137 Note The voltages produced by the Trapezoid Generator may differ depending upon the triggering method GATE IN free running or ATTACK button and by the positions of the A ON D OFF controls This is normal and a consequence of the idiosyncrasies of the EMS circuit designs OUT A OUT B Two outputs are provided These carry identical signals THE VCA Amplifiers have a simple job they amplify or attenuate the signals presented to them Voltage controlled amplifiers VCAs are more sophisticated they allow you to control the amount of amplification or attenuation by applying a voltage to a CV input VCAs exist in every synthesiser that can shape a sound For example you may think that it s the envelope that is changing the volume of a sound but it isn t The envelope is producing a CV that when applied to the VCA causes it to modify the signal passing through it The VCA is one of the fundamental modules th2. EMS SYNTHI TRAPEZOID GENERATOR INTRODUCTION 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 synthesisers The RS510E 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 TRAPEZOID GENERATOR 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 134 ANALOGUE SYSTEMS RS INTEGRATOR 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 Amplitude 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 Ga
3. The decay phase follows the ON stage During this the trapezoid voltage will fall from 5V to 5V in the time determined by the DECAY knob The minimum decay time is approximately 3ms The maximum is approximately 25 seconds OFF The OFF knob performs two functions MANUAL When set to its maximum clockwise position MANUAL the OFF knob allows you to play and use the trapezoid as a contour generator whereby each Gate pulse initiates a fresh A ON D cycle Note 1 The trapezoid does not reset to zero when a new Gate is detected If the trapezoid is in the ON or DECAY stages when the new Gate arrives the Attack will be initiated from the voltage at that moment Note 2 Unlike a conventional ADSR contour generator which will immediately enter its Release phase once the Gate is removed the trapezoid will complete its A ON D cycle no matter how brief the Gate Trigger 136 ANALOGUE SYSTEMS RS INTEGRATOR Other Positions When set to any position other than MANUAL the position of the OFF knob determines the length of time that elapses between the completion of the Decay phase and the automatic start of a new Attack phase In other words at any position other than OFF MANUAL the trapezoid generator repeats and acts as an LFO No Gate is required to initiate this mode of operation If you set the ATTACK to a non zero setting ON to zero and DECAY and OFF to zero the output waveform will be a ramp wave Other settings can generat
4. at allow us to make sounds develop over time The RS510E incorporates an integrated VCA with user controlled signal input and output levels However it has no external CV input The voltage is provided directly by the Trapezoid Generator This means that signals presented to the SIG IN of the VCA will be amplified by the instantaneous Trapezoid level IN USE Input and Output The RS510E VCA offers one signal input SIG IN and a single output SIG OUT each with an associated LEVEL control The input accepts audio signals in the range 10V and at audio frequencies the output will produce a signal in the range 10V Note 1 The position and polarity of the TRAPEZOID OUTPUT LEVEL control does not affect the voltage applied internally to the VCA Note 2 The VCA is designed to modify audio frequency signals If you present a low frequency signal to the input it will be severely attenuated at the output COPYRIGHT NOTICE The circuits incorporated in the RS510E are used under a licence granted to Analogue Systems Ltd by EMS Ltd The name EMS is used under a licence granted to Analogue Systems Ltd by EMS Ltd All rights reserved 138 ANALOGUE SYSTEMS RS INTEGRATOR
5. e triangle waves sawtooth waves skewed triangle waves square waves pulse waves and various shapes of trapezoid waves The maximum OFF period is approximately 5 seconds The minimum is of the order 10ms meaning that the LF signal generated strays well into the bass end of the audio spectrum The maximum amplitude of this signal is approximately 7V CV IN DECAY Input You can modulate the Decay time by presenting a positive or negative CV to the CV IN DECAY input You can use this to change the shape and frequency of the waveform when the Trapezoid is repeating thus creating a huge range of complex waveforms that are particular useful when used as complex modulators for other modules such as oscillators and filters TRAPEZOID OUTPUT LEVEL The output level and polarity are controlled by the TRAPEZOID OUTPUT LEVEL control With this turned fully clockwise the envelope will range from 5V OFF to 5V ON As you turn the knob anticlockwise the signal will be attenuated until with the knob in the 12 o clock position no envelope is generated As you continue to turn the LEVEL knob anticlockwise an attenuated inverted envelope will be output until at the knob s fully anticlockwise position the inverted envelope will range from 5V OFF to 5V ON ATTACK Button The ATTACK button allows you to trigger the trapezoid manually whereupon it will pass through the Attack phase and hold the voltage ON until the button is released ATTA
6. erator generates a four stage A ON D OFF voltage contour that varies from 5V to 5V and back to 5V again The shape described by the Attack On and Decay stages is known geometrically as a trapezoid which leads directly to EMS s use of the term The envelope can be attenuated and inverted if desired Note Ifyou are not already acquainted with the EMS Shaper please set the OFF knob to its most clockwise position labelled MANUAL before continuing to investigate the properties of the Trapezoid Generator The reason for doing so will become clear as you work through the rest of this section GATE IN The Trapezoid is generated when the module receives a gate pulse of approximately 3V or greater at the GATE IN ATTACK With the OFF control set to MANUAL the Attack is initiated upon receipt of a Gate or a Trigger at the GATE IN and the trapezoid voltage will rise from 5V to 5V in the time determined by the ATTACK knob The minimum attack time is approximately 2ms The maximum is approximately 2 seconds This is significantly less snappy than the fast envelopes produced by the RS60 Envelope Generator so sounds controlled by the RS510E can often have a different character to those produced using other contour generators ON This determines the time that the trapezoid voltage will remain at its maximum after the completion of the Attack and once the Gate pulse is removed The maximum ON time is approximately 4 seconds DECAY
7. te is detected and R The Release which determines the speed at which the envelope voltage decays back 4 Time to zero after the Gate is released Gate OFF Gate ON 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 Amplitude 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 oi 4 Time removed the contour remains ON for an additional time determined by the ON Gete ON control Gate OFF 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 ANALOGUE SYSTEMS RS INTEGRATOR 135 IN USE The RS510E Synthi Trapezoid Gen
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