Modular synthesizer

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Steve Porcaro from “ Toto ” with a modular synthesizer

Modular synthesizers are electronic musical instruments that consist of a large number of different components ( modules ) that are used to generate electronic sounds.

Structure and technology

There are modules for sound generation (such as VCO ), modules for changing the sound (such as VCF ) and modules for control (such as ADSR ). The individual modules are connected to one another via cables (patch cables) or switches, sometimes also sliders and patch panels. Thus, with a given number of modules with outputs and inputs, there is a multitude of connection options. The final signal is usually output through a loudspeaker or passed on to a recording device.

An essential feature of analog modular synthesizers is the voltage control of individual parameters of a module. The control voltage (CV for " Control Voltage ") can - for example generated by a keyboard or a sequencer - be applied to the CV input of the VCO, whereby a change in the voltage results in a change in the generated frequency. Further essential parameters are the filter cut-off frequency of the VCF or the amplification of the VCA , which in conventional patches are mostly controlled by the ADSR (often also referred to as EG for "Envelope Generator"). The control voltage range 0 to 10 volts introduced by Moog has established itself as the industry standard. For the control of the VCO and VCF, an exponential characteristic curve of the control voltage was also used, which results in a frequency doubling per volt. There are also deviating control voltage standards, such as B. at KORG (MS-10, MS-20 , MS-50 etc.) or Yamaha . At Eurorack there are also modules that work in the range from -5v to + 5V, both for output and input. With some of these modules you can change the voltage range between -5V to + 5V and 0 to + 10V, mostly via jumpers on the back, many modules also via the digital configuration such as. B. in the case of some MIDI-to-CV / Gate modules.

Other control voltages are referred to as "gate" and "trigger" and do not result in continuous parameter changes, but are used to switch events. The gate signal influences the duration of the event by keeping the parameter switched for a certain duration. This duration can e.g. B. be the time during which a key on the keyboard is pressed. The trigger signal is a pulse of the same length in terms of time, which triggers a signal once without affecting the further course. This can e.g. B. be the start parameter of a sequencer, which takes on its own function after a single "trigger". These control voltages are mostly generated by changing from 0 volts to 5 volts.

Modules

The basic elements of a modular synthesizer include:

  • VCO - (English abbreviation: voltage controlled oscillator) - voltage controlled oscillation generator
  • VCA - (English abbreviation: voltage controlled amplifier) ​​- voltage controlled amplifier
  • VCF - (English abbreviation: Voltage Controlled Filter) - voltage controlled filter
  • VCP - (English abbreviation: Voltage Controlled Phaser) - voltage controlled phaser
  • LFO (abbreviation: low frequency oscillator) - low frequency oscillator
  • ADSR - envelope generator (attack time, decay time, sustain level, release time)
  • Sample and Hold (S&H) - regular sampling (e.g. of a noise signal to generate random sequences)
  • Noise generator (engl. Noise Generator) - produced colored noise, mostly white noise
  • Mixer module - for mixing different control voltages or audio signals
  • Crossfader - to switch between audio signals
  • Sequencer - used to generate a series of musical notes in a predetermined or random order
  • Wave folder - folds an overdriven signal to the zero point instead of cutting it off, creating harmonic notes in the process
  • Modulators
  • DIV (Clock divider) - for dividing an input frequency
  • Wavetable synthesizer - for playing back stored tone sequences
  • DRC (Dynamic range compressor) - makes large amplitudes smaller and small amplitudes larger

Any electronic module that processes voltages can theoretically be used in a modular synthesizer (assuming appropriate modifications). Depending on their quality, modular synthesizers are even suitable for setting up analog computers .

In practice, the individual modules are often mounted in racks . The outer dimensions of the modules then mostly correspond to the 19 ″ standard.

Famous modular synthesizers

Module system from synthesizers.com

In addition to the Moog Modular, for example u. a. was used by Emerson, Lake and Palmer , the systems Roland System 100M, System 700, E-Mu Modular, ARP 2500, EMS Synthi 100, Synthi AKS, Synthi A and the Buchla modules became known. The modular synthesizer called "Formant" also became popular, the assembly instructions of which - written by Cyril Chapman - were published in several follow-up articles in the electronics magazine " Elektor " in the 1970s. This popularity was due to the fact that the commercial systems were almost unaffordable for amateur musicians and beginners at the time and building them yourself promised some cost savings, even if the quality had to be compromised.

A revised construction manual for the formant synthesizer with the designation "Formant-pro MSS2000" penned by Hans-Joachim Helmstedt appeared in 2000. Since many components were no longer available, they contained various adaptations. However, this project was not very successful because the publication was printed by the “Elektor” publishing house with a large number of errors, which made it almost impossible for beginners to build the circuits without errors. The project has therefore now been discontinued.

Currently manufactured modular synthesizers

Doepfer A-100 synthesizer

There are a number of manufacturers who are again or still offering analog modular synthesizers. Many of the product lines from different manufacturers are compatible with one another.

  • Analogue Systems: RS integrator [Eurorack]
  • Analogue Solutions: Concussor [Eurorack]
  • anyware-instruments.de [TINYSIZER]
  • Bananalogue [Eurorack, Fracrak]
  • Birdkids [Eurorack]
  • Blacet Research [FracRak]
  • Buchla
  • Club of the knobs
  • Curetronic
  • Cwejman [Eurorack]
  • Cyndustries Modules
  • Doepfer A-100 [Eurorack]
  • Intellijel [Eurorack]
  • Livewire [Eurorack]
  • Marienberg Devices Germany
  • MFB [Eurorack]
  • Modcan
  • Plan B [Eurorack]
  • PAiA Corporation USA
  • Pittsburgh Modular [Eurorack]
  • serge
  • Synthtech (MOTM)
  • Synthesizers.com
  • Technosaurus synthesizer
  • Wiard

DIY

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Complete do-it-yourself

The self-construction of modular synthesizers according to kits or instructions has meanwhile become common among laypeople as well as professional musicians. There are numerous sites on the Internet that offer instructions and support. In some cases, all the documents required for the replica are provided, from the exposure templates for the circuit board layouts to wiring plans and parts lists. This hobby is often abbreviated as S-DIY or Synth-DIY (DIY stands for Do-It-Yourself). Some manufacturers of modules make the data for their products available as open source, i. H. The circuit board layout, the CAD data for the front panels, possibly the source code for the microcontroller, and the component lists are available for download free of charge and may be reproduced in compliance with your license conditions (mostly Creative Commons). Depending on the license conditions, the modules can even be modified and the resulting product sold, possibly with the name of the original licensor.

Partly self-assembly based on finished circuit boards and front panels

Since the in-house production of circuit boards (PCB) and front panels (English panels) is relatively complex, some manufacturers offer the finished circuit boards and / or the matching front panels in professional quality for sale. The buyer then only has to buy the necessary components (e.g. resistors, capacitors, sockets, potentiometers, plug-in strips, LEDs, ICs, microcontrollers) based on component lists, provided these are not already in stock in the local material warehouse.

Do it yourself on the basis of complete kits

Another variant are complete kits, so-called DIY kits (sometimes also referred to as "full DIY kits"). There are some manufacturers of synthesizer modules (mostly for the Eurorack system) who only offer their products as DIY kits. Other manufacturers offer fully assembled modules as well as identical or slightly modified versions as DIY kits. The DIY kits are sometimes significantly cheaper than the fully assembled version. DIY kits are usually only available directly from the manufacturers or from specialist dealers. In Germany there are currently (as of 2019) very few such dealers to be found. Certain kits are only available abroad. This self-assembly variant is suitable for beginners to advanced users, because the kits are available in all levels of difficulty. This starts with modules on which only a few components have to be soldered, and extends to very complex modules with several hundred components and the subsequent calibration required.

Do-it-yourself housing

Housings are required for all modular synthesizers if you don't just want to leave the modules lying around loose and unprotected. Many users build these housings themselves. The reasons for this are, on the one hand, the high price for finished housings, or the small selection of special dimensions. Beginners in particular often shy away from the sometimes high costs of a housing.

The self-assembly usually only includes the housing itself, which is then supplemented with ready-made power supplies. But there are also kits for the power supplies to buy, or building instructions for the complete do-it-yourself. However, it should be noted that depending on the design of the power supply unit, 230V voltage is present. For safety reasons, laypeople should therefore use ready-made power supplies with appropriate protective devices, or variants that contain a closed plug-in power supply and only have harmless voltages in the housing. Usually this is less than 20V.

In addition to the power supply unit, a special component is always required that enables multiple modules to be connected to the power supply unit. Either circuit boards or ribbon cables with several connectors are used here. The variant with a bus ribbon cable is called "bus cable" or "flying bus cable" (because it usually "flies around" loosely in the housing). Bus ribbon cables are usually only used in small housings ("skiff"). In larger housings, mostly only backplanes are used. The advantage of the backplanes is that they are fixed firmly to the housing by means of screws (usually on the rear wall of the housing), and they are easier to handle later when assembling modules. Larger currents are also possible via this. Several bus boards can be connected to it, depending on the performance of the power supply unit. Usually these are one to three backplanes.

In the Eurorack area, the type and assignment of the plug connections is standardized and identical for all manufacturers. +12, -12V and ground (GND) must always be applied. + 5V are optional because + 5V is only required by a few modules. If the power pack does not provide + 5V, the + 5V can be generated using a small adapter that is plugged into a free socket. The bus boards (but also the bus ribbon cables) also enable the distribution of CV and gate between the modules, provided that the modules support this. This saves the connection of the corresponding modules at the front via the sockets on the front panel and thus fewer patch cables are used.

In the meantime, most manufacturers use special socket strips with a post tray on the backplanes that have a recess on one side and the matching plug has a "nose" at this point. This prevents incorrect insertion. A few manufacturers of backplanes, however, only use simple plug-in connectors without a tub, where there is a risk of plugging in the plug incorrectly: either offset or rotated by 180 °. In the worst case, this can destroy the module that has just been connected or other modules or the power supply unit. That is why it is always important to ensure that the connection is correct. Corresponding notes and markings are usually available on the modules and on the bus boards. Post troughs are always installed on the bus ribbon cables, there is no danger here.

Building a housing yourself can reach any level of complexity:

  • Ready-made, new or old cases (e.g. professional 19 "rack cases or mixer cases, but also old briefcases or travel cases), boxes (some old wine boxes were converted), or cabinets (e.g. old CD cases ), in which only the mounting rails for the modules plus the power supply have to be installed.
  • Completely new buildings made of old or new materials, mostly made of wooden panels, but also made of plastic or metal. There are such housings made of materials cut by laser cutter or CNC milling machine, some of which only have to be put together in a modular system. However, the manufacture from sawn wooden panels that are screwed or glued is more common.
  • Do it yourself from finished components. In the case of finished housings, mostly Eurorack-compatible, in which only the required power supply unit and bus board or bus ribbon cable have to be installed.

Modular software synthesizers

Modular software synthesizers can also be used as a cost-effective alternative. These simulate synthesizer modules implemented in hardware. Examples include:

literature

  • Cyril Chapman, Markus FP Aigner: Formant music synthesizer. 2nd Edition. Elektor-Verlag, Gangelt 1978, ISBN 3-921608-10-4 .
  • Markus FP Aigner: Formant music synthesizer extensions. Description, construction and Game instructions expanded and new formant modules. Elektor-Verlag, Gangelt 1981, ISBN 3-921608-19-8 .
  • Bernd Enders : The sound world of the music synthesizer. The introduction to how a module synthesizer works. Franzis-Verlag, Munich 1985, ISBN 3-7723-7761-0 .
  • Hans-Jochen Schulze, Georg Engel: Modern music electronics. Practice-oriented electroacoustics and devices for electronic sound generation. Military publishing house of the German Democratic Republic (VEB), Berlin 1989, ISBN 3-327-00772-1 .
  • André Ruschkowski: Electronic sounds and musical discoveries (= universal library 9663 Reclam knowledge ). Revised and expanded edition of "Soundscapes" . Reclam Verlag, Stuttgart 1998, ISBN 3-15-009663-4 .
  • Hans-Joachim Helmstedt: FORMANT-Pro. Modular sound system MSS 2000. Elektor-Verlag, Aachen 2000, ISBN 3-89576-099-4 .
  • Peter Gorges: Synthesizer Programming. 4th, unchanged edition. Wizoo, Bremen 2009, ISBN 978-3-934903-64-7 .
  • Florian Anwander: Synthesizer. This is how electronic sound generation works. 8th edition. PPVMedien, Bergkirchen 2015, ISBN 978-3-941531-70-3 .
  • Kim Bjørn, Chris Meyer: Patch & Tweak - Exploring Modular Synthesis. Bjooks, Denmark 2018, ISBN 978-87-999995-1-4 .
  • Rolf-Dieter Lieb, Ulf Kaiser: SynMag - A Guide To Modular Worlds. SynMag Verlag, Rellingen 2019, ISBN 978-3-00-064145-9 .

Web links