Modern Instruments

By definition, a synthesiser makes music by artificial methods, usually by means of electronics. A device of this kind enables a composer to create sounds using an unknown form of instrument, either simulating a new ‘acoustic’ device or something entirely different. In addition, it can create a performance that would be physically impossible for a human musician to play.

Most modern instruments come with a piano-style keyboard, allowing the performer to play several notes at once, so as to create polyphonic material, normally using an even-tempered scale. One unexpected bonus of a keyboard is its ability to play synthesised or sampled instruments in a way that wouldn’t be possible with a real instrument. On the other hand, a keyboard isn’t entirely suitable for playing a replica a of stringed instrument, where subtle changes in tonal quality are obtained by skillful use of a bow or fingering. In addition, the association of the modern keyboard with Western scales makes it less than ideal for African or oriental music.

Apart from synthesisers, there are many other instruments that produce an electrical output for driving a sound generator such as a loudspeaker. Such devices are known as electrophones and are available in the form of electroacoustic, electrophonic and electronic instruments, as described below.

Electroacoustic Instruments

These are usually modified acoustic instruments whose sound is converted into an electrical signal and then manipulated or amplified. The most common examples are the electric guitar, electric piano and electric violin. Oddly enough, with electronic processing introduced into the signal, such devices can create sounds that are nearer to those of a synthesiser. One of the earliest and greatest exponents of applying such techniques to the electric guitar was of course Jimi Hendrix.

Electrophonic Instruments

This group of devices produce sounds directly by electromagnetic or other types of tone generator. Examples include the Compton organ and other early variations of electric organ. Instruments of this kind often imitate the traditional pipe organ and are similarly controlled by means of a standard piano-style keyboard. One example is the Hammond organ, which employs toothed metal wheels and electromagnetic pickups to create a wide range of musical tones.

Electronic Instruments

Unlike other electrophones, this category of instruments use pure electronics to create a signal, requiring electrical energy, but without using mechanical parts in the process. In fact, the sound produced by such an instrument doesn’t really exist until it’s fed into a loudspeaker.

Modern devices of this kind, known as a synthesiser, can imitate acoustic instruments and can be used with samplers containing real sounds. However, early synths were much simpler, consisting of analogue oscillators, noise generators, filters and envelope shapers that the composer interconnected in a creative manner. The idea was further developed by Robert Moog in his voltage-controlled synthesiser. By 1976 the first polyphonic synthesisers began to appear and in the 1980’s the power of the microprocessor was harnessed directly to create sounds. More recently, much of the hardware required for synthesisers has been replaced by computer software.

Despite developments, the traditional organ and modern synthesiser have much in common. They’re usually controlled by a piano-style keyboard, are polyphonic (so they can play several notes at once) and multitimbral (meaning they can play several different kinds of sound or ‘voice’ at a time).

Early Devices

Nineteenth-century electrical instruments include the Componium, the Electroharmonic Piano and the Electromechanical Piano. The Dynamophone or Telharmonium of 1906, devised by Thaddeus Cahill, used alternating current (AC) dynamos and weighed an amazing 200 tons.

The earliest electronic synthesisers used analogue circuitry, as opposed to modern digital technology. One example is the Theremin (or Thereminovox), invented sometime between 1919 and 1924, and finally developed in the US in 1928 by the Russian, Leon Theremin (b.1896). The pitch, covering a range of five octaves, was controlled by moving the right hand around a pole, whilst the volume was adjusted by waving the left hand near a loop aerial. The device itself contained two radio frequency (RF) oscillators, closely tuned to each other, which then created a string-like whine. The movements of the operator’s hands influenced the tuned circuits of the oscillators, changing the sound’s pitch and volume.

The Theremin, played by its inventor at Carnegie Hall

Having appeared in some music halls, this instrument was soon forgotten, although it was used by the Beach Boys on their record Good Vibrations and by the rock band known as Led Zeppelin.

Other early electronic devices included the Ondes Martenot, devised in 1928 by Maurice Martenot (1898-1980), and the Trautonium. Unfortunately for a keyboard instrument, the Martenot could only play one note at a time, a characteristic common to many early devices of this kind.

The Electronic Organ

Electronics found its first challenge in the organ, where the traditional pipes were replaced by electronic counterparts. In advanced electronic organs, separate oscillators were used for each note, with complex keyboard logic to ‘sound’ the appropriate oscillators for each key and stop.

The domestic electronic organ side-stepped these complications by using a set of simple square wave oscillators for the top octave, with frequency dividers for the lower octaves. The results, particularly at the extremes of the keyboard (where the limitations of output filtering became obvious), were often unsatisfactory. Unfortunately, a decent instrument couldn’t be produced at a realistic price until the appearance of the microprocessor. But, unlike many analogue synthesisers, the electronic organ was fully polyphonic: you could press all the keys you wanted, and get all the sounds.

The schematic for this kind of instrument is shown below:-

The Hammond organ, really an electrophonic device, succeeded where many others failed. It incorporated a set of motorised metal tone wheels, each with teeth machined to give the correct pitch, and positioned near a magnetic pickup that extracted the signal. The result was a simple and reliable instrument, with a very characteristic sound, enhanced by its rotating Leslie loudspeaker.

The BBC Radiophonic Workshop created its own unique ‘organ’ from a rack of ordinary test-room oscillators, a small keyboard and a keying unit. As each key was pressed a pentode valve in the keying unit connected an oscillator to the output: each valve had adjustable timing for attack and decay. Limited perhaps, but few instruments today would allow you to tune any key to any pitch.

The Voltage-Controlled Synthesiser

By 1952, music could be created using electronics alone, employing sine wave tone generators to generate pure sounds at a given fundamental frequency, noise generators to create white noise with a wide spectrum and filters to remove anything above or below a given frequency. The Olsen-Belar Sound Synthesiser, a huge machine developed in 1955 by the Radio Corporation of America (RCA), contained oscillators that produced waveforms that included various harmonics.

It was common practice to manipulate the outputs of such machines by means of variable-speed tape recorders. Or they might be combined with real sounds to create what was commonly known as electroacoustic music, although strictly speaking this term refers to electronically-assisted acoustic instruments, as described above.

The Moog Synthesiser

RCA’s Mark II machine occupied an entire room and used paper tape to acquire information. In addition, it cost over $100,000 and was difficult to use. In comparison, the voltage-controlled synthesiser, described by Robert Moog (b.1934) in his 1958 paper to the Audio Engineering Society (AES), combined elements of earlier devices into a device costing less than $10,000. This generated audio waveforms scientifically, shaping and modifying them into the required sounds.

Pioneers of the Moog Synthesiser included Walter (later Wendy) Carlos, who horrified classical musicians with the Switched on Bach album of 1969, although subsequent work, such as Timesteps, showed that the instrument could create truly original material. And productions such as Lucky Man (Emerson, Lake and Palmer) and The Six Wives of Henry VIII (Rick Wakeman) accompanied the synthesiser into mainstream rock music. Other groups of the period, such as Pink Floyd, Yes and Tangerine Dream adopted the new technology, creating some unprecedented artistic works.

The original Moog was far too large to go ‘on the road’, although the later Mini-Moog was far more successful. However, by the end of the seventies other manufacturers, such as ARP, Roland, Oberheim and Sequential Circuits had moved into the synthesiser business, forcing Moog to abandon the industry and to create Big Briar, a company that marketed the Theremin.

The Moog Modular Synth (1967)

Other less influential voltage-controlled synthesisers of the mid-sixties included Don Buchla’s Buchla 100 and Paolo Ketoff’s Syn-Ket. The first of these didn’t have a keyboard, since its designer feared that this could turn the thing into a glorified electric organ, which is what happened to some synthesisers a few years later. However, like the Moog, it was constructed in modular form, allowing the user to change the connections between the various elements. The Syn-Ket, on the other hand, did have a keyboard, making it easier to play, but its components were hard-wired together.

The Principles of Voltage Control

Moog’s invention consisted of simple elements that influenced each other by control voltages. How they were used and connected was left to the composer. Musically, the results were often awful: considerable skill and artistry was needed to rise above the mundane. Worse still, since analogue voltages determined the pitch of the oscillators, there were problems with tuning, often due to temperature changes as the equipment warmed up. Despite this, the device remained a dominant force into the age of the microprocessor. In fact, such machines still exist and are even fitted with MIDI.

The main elements, as typically connected, are shown below:-

The Keyboard

This was usually monophonic, so only one note could be played at a time, although some synths had dual keyboards or used special electronics to give duophonic operation. The control voltage (CV) it produced represented the pitch, usually on a scale of one volt per octave, 0.5 volt per octave or one millivolt per hertz (mV/Hz). CV signals weren’t standardised. For example, zero volts could correspond to the bottom note (higher keys giving a positive voltage) or the centre note (keys to each side going positive or negative). The latter was convenient for tuning, since zero volts was at middle C or A, and gave linear results across the keyboard. The pitch of a decaying note was kept in a sample and hold circuit until the next key was pressed. The keyboard also produced a gate signal (positive 5, 12 or 15 volts) to indicate that a note had been pressed.

Some keyboards also generated a trigger pulse the instant a key was pressed. In some instruments, such as the ARP Odyssey, a small change in CV also created a trigger pulse. A second note could then be played whilst another was held (for playing in legato), providing a form of duophonic operation.

Major Elements

The following elements, in various numbers, could be found in most synthesisers:-

Voltage-Controlled Oscillator (VCO)

This usually provided square, sine and triangular audio waveforms, often with a variable mark-to-space ratio. The initial pitch of each VCO had to be adjusted, also the sensitivity to voltage control, so as to give satisfactory tuning across the entire keyboard. An extra control voltage input was often used with a low-frequency oscillator (LFO) to provide vibrato.

Voltage-Controlled Filter (VCF)

This was used for ‘tuning’ the frequency spectrum of any sound (often the output of the synthesiser’s white noise generator) under control of the keyboard. Each VCF usually had controls for the initial frequency and filter quality (Q), both of which were often voltage-controlled. Some VCFs could also oscillate, allowing them to be used as extra VCOs.

Envelope Shaper (ES)

This accepted a gate signal, usually from the keyboard, and used it to create a varying control voltage. ADSR shapers had controls for attack (the initial rise), decay (the fall as a key is held), sustain (the level as a key is held) and release (the fall after a key is lifted). An ADR shaper was a simpler version with three parameters. Most shapers were fully voltage-controlled.

Voltage-controlled amplifier (VCA)

This was often used to regulate the volume of the output of a VCO under the control of an envelope shaper. VCAs typically worked at 10 to 20 decibels per volt (dB/V), although the polarity varied. With a zero voltage at the control input, most VCAs were at their default or ‘initial’ gain, typically between 0 dB and +10 dB.

Sample and Hold (S&H)

This circuit retained a control voltage after a note on the keyboard had been released, thereby ‘memorising’ the pitch of any note that required a long decay. Its inputs were usually connected to the keyboard’s CV and gate (or trigger) outputs.

Other Components

White Noise Generator

This provided random noise over a wide spectrum of frequencies. Its output was often fed into a VCF so as to create impulsive or atmospheric sounds.

Random Voltage Generator

The control voltages created by this component could introduce an element of chaos into any work. The voltage swing and frequency was usually set by Range and Variance controls.

Control Voltage Modifiers

A trapezoid could slow down rapidly changing signals, whilst inverters would reverse control voltages. In addition, other voltage modifiers could introduce control offsets or level changes.

Connection Systems

Various connection methods were used, including 3.5 mm jack cords, popular on American and Japanese products. Electronic Music Systems (EMS), who took the analogue synthesiser to its zenith, employed patch-pins on matrix boards. The latter had virtual earth inputs, whilst the patch-pins contained resistors, allowing numerous sources to feed a single destination, with the value of a patch-pin’s resistor (denoted by the colour of the pin) setting the sensitivity of an input.

Hybrid Synthesisers

The voltage-controlled synthesiser offered more than anything that came before, but was difficult to use. Larger machines were expensive and clumsy, the best results often being obtained by accident. The arrival of the microprocessor was to see both its final development and eventual demise.

At the end of the seventies, most processors were too slow for creating or modifying real sounds. Instead, new synthesisers employed such devices to act as a ‘front end’ for conventional voltage-controlled technology. One early machine of this type, the Yamaha CS80, looked like a large electronic organ, but was really processor-controlled. Whenever you pressed a note, that key would be assigned to a specific voltage-controlled oscillator, so providing true polyphonic operation.

Other synthesisers in this category must include the famous Prophet 5 from Sequential Circuits and the Oberheim OBX8. These hybrid machines came as a shock. In appearance they were unlike any ‘classic’ synthesiser, but behind the new frontage an analogue machine was lurking.

Hybrid Workings

Most hybrid machines used a single microprocessor (micro) for all the tasks, although some instruments employed a separate processor, often a customised device, to provide polyphonic key assignment. A typical schematic is shown below:-

In most instances, the operational switches and keyboard contacts were wired to a parallel port on the microprocessor via a scanning ‘XY’ matrix. Analogue signals from variable controls, including bend wheels and swell pedals, were multiplexed and sent via a digital-to-analogue converter (DAC) to the micro. From the micro, switching and control data was sent to an analogue-to-digital converter (ADC) and on to a demultiplexer that sent signals to the appropriate destinations.

Most machines kept the micro’s operating system (OS) and preset voices in read-only memory (ROM), whilst the user data was kept in battery-backed random-access memory (RAM). In addition, the data could be dumped to or loaded from an audio cassette recorder, although this was often unreliable and was slow to operate.

One very important job for the micro was key assignment, the process of choosing which oscillator and envelope shaper was operated by which key. Typically, pressing one key selected, at random, any one of eight oscillators. Pressing another key simultaneously ‘fired’ the next oscillator, and so on, until the maximum number of oscillators, usually eight, were sounding. If another key was pressed (and all the other oscillators were operating, perhaps with their envelope level decaying) the very first oscillator had to be ‘grabbed’ for the new key, possibly truncating the first note.

The tuning of such machines could be very complicated. Most oscillators (once you identified the one that was in operation) had at least three adjustments, and an iterative process was required to give good results across the keyboard. Typically, tuning a Yamaha CS80 would take two or three hours.

Digital Synthesisers

The high-speed processor of the eighties could manipulate audio data directly, and so removed the need for analogue circuitry overnight. Robert Moog’s dream had come to an untimely (or timely) end.

A wavetable synthesiser, such as the PPG Wave, kept one complete cycle of each sound in RAM or ROM. When a key was pressed, the data was clocked out into a DAC at the desired rate. The contents of a wavetable could be modified, or parts of different wavetables could be joined to create new tables. The Wave also sampled real sounds that could then be edited and looped. Unlike earlier synthesisers, it included floppy disk drives and a visual display unit (VDU) for editing.

The Fairlight Computer Musical Instrument (CMI) was far more advanced. In fact, this synthesiser was a specialised variation of a standard mini-computer, complete with a graphical display controlled via a light pen. In its final form, this machine incorporated real-time audio recording on eight ‘tracks’.

These machines were large, powerful and expensive. Moreover, they needed considerable skills to fully exploit their potential. The products that followed were entirely different. The revolution in consumer musical products had begun.

The Last Synthesisers

Digital synthesisers of the later generation often contained customised integrated circuits. Even so, the typical schematic, as shown below, was similar in many ways to a desktop computer:-

Some machines, especially older models, used two processors. The main device worked with elements common to any computer, such as RAM, ROM, disk drives, MIDI ports, other ports and VDU. The sound processor, often a fast custom chip with its own RAM and ROM, provided digital signal processing (DSP). The latter device was connected to the real world via an ADC or a digital interface (DIF) and often had a separate hard disk drive for sound samples.

One early form of DSP was frequency modulation (FM), which first appeared in Yamaha’s DX7 and its successors. The process of FM between two or more tones, known as operators, is simulated by digital computation to create complex sounds, often very musical and penetrating. The results seem to have little in common with the operators, making it difficult to create sounds ‘from scratch’. But Yamaha satisfied most of its customers by supplying the machine with an extensive range of preset sounds. It also accepted RAM and ROM cartridges that expanded the choice still further.

Many digital machines, often using highly innovative ideas, followed on from these pioneers. But perhaps the greatest advance was the increase in ease of use for the musician.

Digital Samplers

By incorporating an analogue-to-digital converter (ADC), the digital synthesiser became an audio sampler. The E-mu Systems Emulator II, one of the first machines of this kind, employed 12-bit technology, although the sound quality was very impressive. Its place in ancient history is confirmed by its use of two cumbersome 5¼ inch floppy disk drives.

The Roland S50, with its provision for a VDU, was a pioneering keyboard machine that kept samples on a 3½ inch floppy disk. This was followed by the rack-mounted S550, also giving multiple outputs. However, the ‘industry standard’ for many years in the world of sampling was the Akai S1000.

A new generation of machines soon appeared, with samples matching the quality of digital audio. They included the E-mu Proteus and Procussion, both playback-only samplers containing a vast repertoire of instruments, showing a high technical quality and sampling artistry. Also, they exploited MIDI to the full, allowing sixteen sounds to be played at any time, each with sixteen-note polyphony.

Beyond Hardware

Today, many older synthesisers, including those ancient analogue devices, can be emulated by using suitable software on a fast desktop computer. Often, these new applications don’t require special hardware, apart from standard audio inputs and outputs. For those who want to go further, synthesisers, samplers and digital audio recording can be installed as plug-in PCI cards. As processor speeds continue to increase, even these cards are likely to be replaced by more advanced software. The days of the synthesiser are over: we’re now in the world of ‘desktop composing’.


1997 Grolier Multimedia Encyclopedia, © 1997, Grolier Inc.

ATPM, Moog Synthesiser, © 2002 David Ozab

©Ray White 2004.