The Charm of Synths

Two versions of the Switched-on Bach album cover appeared. The one above was the first one used. Unfortunately, the synthesizer is incorrectly set up. The earphones are plugged into the input. The output isn’t connected to anything, offering silence as the synthesizer’s final product. A second cover, with a standing Bach, corrected these faults.

It is now over fifty years since I first heard a recording of a synthesizer, and became intrigued (but not enthralled) by this rather artificial music production machine, as were many other young people. As is frequently the case, the older generation was more sceptical. Wendy (then Walter) Carlos (1939 – ) performed on and programmed the synthesizer, Benjamin Folkman (? – ) performed on supplementary keyboards, while Rachel Elkind (1939 – ) produced. The album was Switched-on Bach (1968), and referred to ten works of Johann Sebastian Bach (1685 – 1750) in the public domain.

These pieces were played on a modular Moog synthesizer. The recording process was labour intensive, and necessitated a close cooperation with Robert Moog (1934 – 2005), designer of the instrument. A custom 8-track recording machine was built by Carlos from components. The synthesizer was monophonic, meaning only one note could be played at a time. This meant that each track had to be added individually. Each note had to be released before the next note could start. In addition the synthesizer frequently needed to be tuned, because of tonal drift. The album took approximately five months and about one thousand hours to produce. By 1974 over a million copies of it had been sold.

Why anyone would want to buy an off-the-shelf synthesizer is beyond my comprehension. Synths are ideal DIY projects. Despite this, there are several approaches that can be taken to build one.

YouTube contains a number of sites dedicated to music and electronics. The one I have found most useful is Notes & Volts. Its three basic Arduino videos provide insights that go beyond the introductory tutorials provided by Jeremy Blum: Arduino on a Breadboard; Arduino as ISP; Arduino on a Proto-Board. It also has 9 videos about MIDI for the Arduino. All of these provide insights that extend far beyond the Arduino. There are also several music related projects, including an Arduino Granular Synth and a Teensy Synth. More information about the Teensy Synth is available at Arduino Slovakia. Teensy is a development board made in Sherwood, Oregon. The latest version, 4.0 uses an ARM Cortex-M7 processor at 600 MHz. However, the Notes & Volts synth specifies version 3.2 using a much less powerful ARM Cortex-M4 processor at 72 MHz.

Another approach is to find a kit, buy it and build it, slavishly following provided instructions. Elektor is probably the best place to look. It is a bi-monthly electronics magazine first published in Dutch in 1960, and in English since 1975, renamed ElektorLabs magazine in 2019. It offers a wide range of electronic projects, background articles and targets engineers as well as enthusiasts. Synthesizers are just one area of many, where PCBs, kits and modules are available. Microcontroller based projects have downloadable source code and (sometimes) executable files available free of charge from their website, along with PCB and other artwork.

People who regard assembly of an IKEA flatpack, as DIY, will be pleased to hear that Eurorack is the flatpack standard for modular synths. The format was originally specified in 1996 by Doepfer Musikelektronik. There are two basic technical specifications that have to be met:

The starting point for constructing a Eurorack is usually a case and power supply. DIY cheaters, will be able to buy these either separately, or together. The electrical specifications require the use of a red stripe to mark the -12V supply on each module’s power cable, and include keyed connectors which physically prevent modules from being plugged in incorrectly. 3.5 mm monojacks are used to connect

Purists will then populate their rack with modules containing sources and processors.

Sources – characterized by an output, but no signal input; it may have control inputs:

  • VCO – Voltage-controlled oscillator, a continuous voltage source, with an output signal that may be a simple or dynamically modified waveform.
  • Noise source – A random voltage output typically providing white, pink and/ or low frequency noise.
  • LFO – A low-frequency oscillator, optionally voltage-controlled. Typically used as a control voltage for another module.
  • EG – An envelope generator is a transient voltage source, typically configured as ADSR (Attack, Decay, Sustain, Release) to control the amplitude of a VCA.
  • Sequencer, aka Analog Step Sequencer, may act as a source or a processor.

Processors – characterized by a signal input and an output; it may have control inputs:

  • VCF – Voltage-controlled filter, attenuates = lessens frequencies below (high-pass), above (low-pass) or both below and above (band-pass) or between (band-reject = notch) certain frequency. Typically with variable resonance, sometimes voltage-controlled.
  • VCA – Voltage-controlled amplifier, typically a unity-gain amplifier which varies the amplitude of a signal in response to an applied control voltage, with a linear or exponential response curve.
  • LPG – Low pass gate using a resistive opto-isolator to respond to the control voltage.
  • RM – Ring modulator where two audio inputs create sum and difference frequencie but suppress original signals.
  • Mixer – A module that adds voltages.
  • Slew limiter – Sub-audio lowpass filter.
  • S&H – Sample and hold, typically used as a control-voltage processor.
  • Sequencer- (see above).

To populate their rack appropriately, the ModularGrid database can be used to find suitable modules. As this is being written in 2019-10, there are 8 525 Eurorack modules to choose from, that have populated 224 551 racks in the Eurorack universe.

The advantage of a modular synth is that it can be whatever one wants it to be. The user is the designer. It is relatively easy to customize. It also allows the user to start off small, and to expand gradually. This has a second advantage. It takes time to learn how to use gear. One can start off by reading the manual, but then one has to experiment. Patching = connecting with 3.5 mm monojack cables, is part of this process. If a module turns out to be of limited use, it can be sold – or even traded.

One Reply to “The Charm of Synths”

  1. Earlier today, I received four questions with respect to four different weblog post, including this one. Since I didn’t yet know the person, I thought I would write to him, just to make sure he existed. The reply back indicated a non-existent e-mail address. Thus, I have sent all of these questions to the bin.

    Despite this, I though two of his questions warranted a response. This is the second one. Will there be an entire orchestra made of electric instruments ? Many synthesizers are capable of imitating different instruments, and with a modular synthesizer it is possible to make or buy modules that can imitate specific ones. Thus, a single modular synth can imitate an entire orchestra. If you want to work more in this field, then I would suggest you investigate the Eurorack synth system, and perhaps even try making a module. People have developed businesses by doing this. As a teacher, I had my students make very primitive Arduino based modules that produced sound. Despite encouraging many of them to go on to make synths, none of them did so – to my knowledge.

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