Control Voltage Generators & Modifiers

Analog Shift Register w/ input attenuator pot (ASR)

The ANALOG SHIFT REGISTER (ASR) is a sequential sample and hold module for producing arabesque-like forms in musical space (see diagram). Whenever pulsed, the previously held voltage is sent down the line to three consecutive outputs to produce the electrical equivalent of a canonic musical structure. A pulse output permits linking two or more Analog Shift Registers together to form longer patterns.

Dual Analog Shift Register (2ASR)


Dual Comparator (COM)

The DUAL COMPARATOR (COM) provides several often useful house-keeping functions within the Serge system:
  • Logical Decisions: If the + input is greater than the - input, then the output will be high. If not, then the output will be low. 
  • Level Detection. A pulse will be generated whenever an input voltage reaches a pre-set threshold. For example, when an envelope detector reaches a certain loudness level, it can be used with the Comparator to generate a pulse to activate or de-activate other events programmed within the synthesizer. 
  • Voltage variable pulse width modulation of any of the Serge oscillators. 
  • “Squaring” audio signals, whereby frequency related pulses are derived from an input signal. These pulses can be used for frequency sub-division (via a Dual Slope Generator or Sequencer), or as raw audio, rich in harmonic content. 
In addition to the +/- inputs, each of the Comparators include a front-panel knob to manually set a threshold.

÷ N Comparator (NCOM)

The ÷ N COMPARATOR (NCOM) consists of two sections: a comparator and a voltage-controlled pulse divider. The divider section outputs a pulse once every “N” comparator pulse, where “N” is a number from 1 to 31, settable with a control voltage at the divider's VC input (or manually via the divider's control knob). Additionally, the Divider outputs a staircase wave with “N” steps. This will produce whole-tone steps when plugged into the 1 V/Oct input of a VCO.

This module has two distinct areas of use (in addition to the normal functions of the comparator):
  • For audio frequencies, the divider can be set to output sub-divided frequencies with digital precision. Output frequency depends on “N”. If “N”=2,3,4, etc., the output frequencies will be an octave, an octave and a fifth, or two octaves below the input, respectively. Because “N” is voltage controllable, arpeggios and various melodies can easily be programmed. The nature of this type of division (integer division) results in frequencies that fall along the sub-harmonic series, a series that has great tonal charm. 
  • For sub-audio frequencies, the divider acts like a counter, outputting a pulse only after “N” number of input pulses. Input pulses can be fairly random, or regular. This capability is especially powerful for determining tempos and rhythmic patterns when using several sequencers (especially if the “N” VC input is taken from one of a sequencer's rows of controls). In a more random situation, using a microphone preamp/detector as input, the divider might be set to count how many times a sound of a certain loudness will have occurred, and be set to trigger an event upon reaching the count. Since the count can be made variable (from 1 to 31), fairly complex and subtle interactions can be generated.

Dual Schmitt Triggers (STR)

The DUAL SCHMITT TRIGGER (STR) is similar to the Dual Comparator, except that it has been optimized for squaring up audio signals. The Schmitt Trigger is a single-input comparator with hysteresis. Hysteresis means that the switching thresholds are different for an input signal depending upon whether it is going up or down. This feature can be used with an envelope and VCA functioning as a noise gate to reject low-level background noise in audio applications. The Schmitt Triggers can be used for level detection, plus they have a function unique to the module: both sections of the module can be used as a “set-reset flip-flop”. Essentially, this is a memory element. A pulse or level into the SET input sets the R/S output high. This output will stay high independently of the activity at the SET input. It is reset to zero when the RESET input receives a pulse of sufficient level.

Boolean Logic (BLOG)

From Carbon111's Serge Modular Index:
"This is the best way to combine triggers together in various ways. Of course, can be used for making audio too. One guy says he uses it as a blinky-lite indicator to show the status of signals in his system. This is one of Rex's ideas, offering two inverters, and OR, AND, and XOR gates."

Pulse Divider (PDIV)

From Carbon111's Serge Modular Index:
"I think this is one of Rex's creations. Looks simple enough: feed a pulse train in, get multiple simultaneous divided outputs. Other pulse dividers I've seen from other manufacturers provide outputs that are powers of two (2,4,8,16...) but don't provide 5,6, or 7 or any odd-numbered divisors. Providing the odd divisors aids greatly in creating polyrhythms."


Dual Transient Generator (DTG)

The DUAL TRANSIENT GENERATOR (DTG) provides two independent outputs with voltage controllable rise and fall times. This module is identical to the Dual Universal Slope Generator except that it does not have all of the front panel features. This module is a useful, space-effective unit to be used for many of the same functions as the Dual Universal Slope Generator. Common uses of the Dual Transient Generator are for simple “AR”-type envelope generation, as a dual voltage-controlled low frequency oscillator, or as a voltage-controlled clock (especially suitable for clocking the Touch Keyboard Sequencer or any of the Sequencer Programmers). These functions can be patched with the Dual Universal Slope Generator, but since many of the features are left unused in these patches, the Dual Transient Generator provides the same function while using less front Panel space.

Dual Universal Slope Generator (DSG)

The DUAL UNIVERSAL SLOPE Generator (DSG) is the ultimate patch-programmable control voltage generator in the Serge system. At least one (DSG) is recommended for almost every Serge system. and in most cases, a number of these are desirable. People familiar with our previous series of “slewing” modules know about the importance of this kind of function in a large patchable synthesizer system. For those unfamiliar, it is advised that the various applications as outlined here and in the Serge Owner's Manual are studied. The uses of this module are numerous, some duplicating functions found on other synthesizers, some totally unique to the Serge system. Most systems require a number of control voltage generators to control the various signal processors and modifiers. Sources of trigger, pulses (clocks), control voltage processors (portamento's), regular repeating voltages (LFO's) are standard synthesizer requirements. The Dual Slope Generator is the main module providing these functions in the Serge system.

The Universal Slope Generators are unity gain voltage followers with voltage controllable slopes. The range of control is exponential, extremely wide, and the Rise and Fall times can be controlled independently. The range of the Slope Generator is from sub-sonic to high audio frequency. Trigger inputs and trigger outputs allows each section of this dual module to function as a transient (envelope) generator, pulse delay, or in a “cycling mode” (to produce an LFO or clock). Since the Rise and Fall times are voltage controllable, this adds another dimension to the above functions. Two VC inputs are available, one is calibrated at 1 volt per octave (within about 3%), and the other is fully adjustable in the negative and positive direction. This VC input can control either the positive slope (rise), negative slope (fall), or both. The linearity and accuracy of the slewing amplifiers allows them to be used in the most exacting applications, such as processing the output of a keyboard or sequencer to produce portamento functions. Note that this portamento function has a separate rate control for rising notes and falling notes... An interesting portamento effect. Among the functions which one Slope Generator can be patch-programmed to perform are the following:
  • VC Transient Envelope Generator. The envelope is simply started with a trigger, or may be used with a gate input to obtain a steady-state sustain level on the envelope. This envelope will repeat if the END trigger output is connected to the TRIG IN input. 
  • VC LFO. Patched as mentioned above, a wide-range, low-cost, space-efficient Low Frequency Oscillator can be patched when needed. The Slope Generator is often used as an LFO since it is more cost effective than a regular oscillator switched to a low frequency range. it has a built-in LED to show its current output level, and it has a synchronized trigger output. The waveform can be set from saw to triangle, and the rising ramp can be voltage controlled independently of the falling ramp. 
  • VC Portamento device. The accuracy of these devices makes this portamento function useful with keyboards and for generating control voltages of arbitrary shapes and times with computer control. Analog control of slopes allows the computer to do less “number crunching”, and frees the processor from time-consuming routines that are more easily handled in this low-cost multifunctional hardware. 
  • Envelope Follower (Detector). The decay rate is voltage controllable with the unique function that under voltage control, the response may be moved from positive peak detection to negative peak detection. 
  • VC Pulse Delay (Monostable). When the unit is triggered, it will produce an envelope set by its Rise and Fall knobs (and VC's) and then the END pulse will go high. This may be used to trigger another Slope Generator, ADSR, or advance a sequencer. 
  • Sub-Harmonic Series Generator (Divider). If a series of triggers are applied to the TRIG IN jack that are faster than the total rise plus fall time, then the unit will divide the incoming triggers by a whole number. This allows the user to program synchronized rhythmic relationships (such as 2 against 3, 13 against 11, and so on). If the Slope Generators are set to audio frequencies, and the incoming triggers are in the audio range, then the output will be the sub-harmonic series. This is similar to the “hard sync” sound found in other synthesizers (and is the main reason that it is not included on Serge VCO’s). 
  • Audio Oscillator. The range reaches 4000 Hz, and the waveform has variable symmetry (saw to triangle). 
  • Non-Linear Audio Processor. The slew limiting is voltage controllable, so a sawtooth wave input will progressively be transformed into a triangle wave. This aspect allows the unit to be used as a low-fidelity VCF! 

Dual Voltage Controlled Clock (CLK)

This module is very similar to the left cell of the VC TIMEGEN CLOCK (TGC) found on a few M-Class modules.

The TGC description indicates "...the left cell 'blue' out being an asymmetrical triangle wave & 'red' out being a 50% duty cycle square wave output which stays constant through the manual 'freq' POT range in combination with the 'both' position selected w/ external CV -- BUT with the ability to modify the duty cycle (pulse width) of the output(s) using external CV source from either the front or the back of the pulse by selecting 'rise' or 'fall' on the CV source select switch. That way you can create syncopation in the rhythm patches & pulse width mod in the audio range use."

So... That, with the functions described above found on the right cell as well.

Extended Envelope Generators (ADSR)

The EXTENDED ADSR (ADSR) is a complex envelope generator using the four segment envelope normally encountered in keyboard synthesizers. This ADSR, however, is designed with extra features such as voltage control of each section, an initial voltage controllable delay time, switchable slopes, and a master voltage control. Each segment may be manually set and voltage controlled, so the module may be used with or without keyboards as a versatile, programmable control voltage generator. In addition to the normal Attack, Decay, Sustain, and Release segments, an Initial Delay time is included. This allows multiple envelopes to be initiated from a single trigger or gate, delayed with respect to one another. Ramps for the Attack and Release segments can be switched to either linear or exponential slopes with the three-position switch. In the left [i.e. top] position, the Attack will have an exponential slope. In the middle position, both the Attack and Release will have an exponential slope, and in the right [i.e. bottom] position, all will have linear slopes. A master 1V/OCT control will control all slope times to allow such effects as decreasing the entire envelope time as the pitch of an associated oscillator increases. This phenomenon is typical of many acoustic instrument envelopes.

Smooth / Stepped Generator (SSG)

The SMOOTH & STEPPED FUNCTION GENERATOR (SSG) is a complex multi-functional module to provide various slew and sample functions.
  • The Smooth section will place a positive and negative slew (glide) on a changing input voltage for lag effects, voltage controlled portamento, and non-linear, low frequency filtering. With the CYCLE jack patched to the input, the unit will oscillate yielding a voltage controlled triangle wave LFO. A high level into the HOLD input will hold the current output level, whether the unit is oscillating or processing an external control voltage. This is identical to a track-and-hold function. 
  • The Stepped function can be used as a sample-and-hold with voltage controlled slew rate limiting. Slew rate limiting limits the size of the step at the output. For example, with a random voltage input and the step size set to a small value, the output is a random voltage that varies only slightly from step to step, gradually covering the entire range of the input voltage. No large changes in the output will be allowed. With the Cycle jack patched to the input and a trigger applied to the Sample input, complex staircase waveforms are generated. 
  • The COUPLER is an internal comparator comparing the Smooth and the Stepped outputs. This is useful for generating complex control voltages and for patching a random voltage generator. In fact, the Random Voltage Generator module is a Smooth & Stepped Generator internally patched to function exclusively as such. If random voltages are often used, a Random Voltage Generator is a more space-efficient module; but if seldom used, the Smooth & Stepped Generator can be patched when needed (and can be used for other functions when not used as a random voltage generator). Note that a Noise Source is needed for use of the Smooth & Stepped Generator as a random voltage generator.


Noise Source (NOI)

The NOISE SOURCE (NOI) generates both white and pink noise waveforms. The S/H Source output produces the necessary input for a sample and hold function to produce equi-probable random voltages, similar to a 1/F distribution function. Additionally, the Noise Source features a random voltage output which can be stepped through random voltages by triggers or from a pushbutton on the module.

Random Source (RS)

[The RANDOM VOLTAGE GENERATOR (RVG) produces random voltages which vary smoothly or in a step-wise manner. Random timing pulses are also available. Rate of change of all outputs is voltage controllable over a wide range.] The RANDOM SOURCE (RS) allies a Noise source with a Random Voltage Generator in one single module.

Random Voltage Generator (RVG)

The RANDOM VOLTAGE GENERATOR (RVG) produces random voltages which vary smoothly or in a step-wise manner. Random timing pulses are also available. Rate of change of all outputs is voltage controllable over a wide range.

Dual Random Voltage Generator (2RVG)


Quadrature Oscillator (QUO)

The QUADRATURE OSCILLATOR (QUO) provides signals and features which make it ideal for controlling the Quad Panner. It generates two sine waves which are always displaced 90 degrees in phase from one another. This phase difference provides exactly the correct relationship for swirling a sound through quadraphonic space in a circular pattern (using the Quad Panner). Since the Oscillator has a basic range from longer than 20 seconds per cycle to 500 cycles per second, many effects can be produced. Swirling a sound at an audio rate produces interesting spatial and modulative effects. Additional features include linear VCAs for each of the outputs so that spatial swirls can be made to decrease in size, effectively spiraling inward. A HOLD input "freezes" the outputs whenever pulsed high. Thus a swirl can be stopped at a given location, with the sound just "hanging there" until operation is resumed. Switches on the panel allow disabling the oscillator, a feature which has been found to be useful for live performance. The use of this module is not limited to Quad Panning. The phase separation between the oscillator's outputs provides for many interesting cross-fading effects when they are used to control other Serge modules.

Quantizer (QUAN)

The QUANTIZER (QUAN) provides a simple means to turn any control voltage into voltage steps corresponding to well tuned (equal-tempered) tones of the musical scale. It is scaled to 1 volt per octave. Thus, a zero to +5 volt envelope at the Quantizer's input produces a staircase of voltages corresponding to a chromatic scale spanning five octaves.

If patched to the 1 volt per octave input of an oscillator tuned to “E”, a gradual slope of 1 volt applied to the input of the Quantizer will produce the following steps of the musical scales:

(normal chromatic scale)

If the 1/6 Scale Select is HIGH, then the scale produced will be:

(whole-tone scale)

If the 1/3 Scale select is HIGH, then the scale produced will be:

(scale of major third steps)

If both the 1/6 and 1/3 inputs are high, the scale will be:

(alternating half-step/minor third step)

Since the Scale Select inputs can be activated very quickly, the Quantizer can produce a very wide variety of tonal effects, quickly moving between four different types of musical scales (chromatic, whole-tone, the augmented triad, and a six-step major-minor scale often heard in certain oriental [sic] musics).

The basic Quantizer features seven or eight channels, depending on the model. Available as a “stand-alone” module, the Quantizer has seven channels and takes up two inches of panel space. Other models are available, however, with some of the channels “hard-wired” to provide quantized outputs for other Serge modules such as the various Sequencer Programmers and the Touch Keyboard... Accuracy of the Quantizer is 3 cents maximum deviation from the ideal equal-tempered semi-tone over a five octave range (i.e. just about the limits of pitch sensitivity of the human ear). Response time for all channels is about 8 milliseconds.

Quantizer (used with SQPs) (QSEQ)

[See Quantizer (QUAN)]

The Sequencer Programmer Quantizers take up only one extra inch (in addition to the Sequencer Programmer - see section on Sequencers).

Quantizer (used with TKB) (QTKB)

[See Quantizer (QUAN)] 

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