The synthesiser would only become a consumer product
if it was ‘user friendly’. At an opportune moment in the early
eighties the microprocessor arrived, and for the first time it
was possible to build machines that suited real musicians.
Microprocessor control was used in these instruments to give a ‘live’ polyphonic performance. Early examples include the Yamaha CS-80 and Sequential Circuits Prophet V. These hybrid machines came as a shock — in appearance they were unlike any ‘classic’ synthesiser, but behind that new front an analogue machine was lurking.
The Workings of Hybrid Machines
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Most machines use a single microprocessor (micro) to perform all tasks, although some instruments use a separate dedicated processor (sometines a customised device) for polyphonic key assignment.
 
Operational switches and keyboard contacts are connected to a parallel port of the microprocessor via a scanning X-Y matrix. The analogue signals from variable controls, bend wheels and swell pedals are multiplexed and sent via a single digital to analogue converter (DAC) to the micro. From the micro switching and control data is sent to an analogue to digital converter (ADC) and on to a de-multiplexer which directs signals to their correct destination.
Early machine employ read-only memory (ROM) to store the operating system and any preset voices. Battery-backed random-access memory (RAM) holds any user data which can also be dumped to or loaded from an audio cassette recorder — but this may be unreliable.
One of the most important jobs for the micro is key assignment — choosing which oscillator and envelope shaper is operated by which key. Typically, pressing the first key selects, at random, any one of eight oscillators. Pressing another key at the same time ‘fires’ the next oscillator, and so on, until the maximum number of oscillators, usually eight, are in action. If another key is pressed (and all the other oscillators are in action, perhaps with their envelope level decaying) the very first oscillator has to be ‘grabbed’ for the new key, possibly truncating the first note.
Tuning such machines is difficult. Most oscillators (once you have identified the right one) have at least three adjustments and an iterative process is needed to give good results across the keyboard. A CS-80 needs an entire morning!
All-Digital Synthesisers
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  As soon as the high-speed micro arrived it was possible to
manipulate audio data directly. The need for analogue
circuitry disappeared overnight — Robert Moog’s dream
had come to an untimely (or timely) end.
Wavetable synthesisers, such as the PPG Waveterm, stored one complete cycle of each sound in RAM or ROM. When any key was pressed the data was clocked out into a DAC at the desired rate. The data making up the wavetable could be modified, or elements from different wavetables could be joined together to create new tables. It also sampled real sounds which could then be edited and looped. Unlike earlier synthesisers it included floppy disk drives and a visual display unit (VDU) for graphical editing.
The Fairlight Computer Musical Instrument (CMI) was far more advanced — it used a mini-computer featuring a light pen and graphical display. It eventually incorporated real-time audio recording on eight ‘tracks’.
The E-mu Systems Emulator II was one of the first high quality sampling machines and incorporated two 5.25 inch floppy drives. It used 12 bit technology — but with remarkable quality.
All of these machines were large, powerful and expensive. Moreover they needed considerable operational skill to exploit their potential. The products that followed were completely different. A revolution in consumer musical products had begun.
Advanced Digital Machines
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These synthesisers use customised chips, enabling them to enter the world of ‘super machines’ at much lower cost.
 
They invariably use two processors. The main processor interfaces with devices common to any computer — RAM, ROM, floppy disk drive, hard disk drive, serial port, MIDI connection and VDU. The sound processor, which needs to be very fast, is often a custom chip. This deals with digital signal processing (DSP), usually in conjunction with its own dedicated RAM and ROM. It connects to the ‘real’ world of audio via a DAC, an ADC or a digital interface (DIF). It may also connect to a hard disk drive containing sound samples.
One early example of DSP is frequency modulation (FM), which appeared in Yamaha’s DX-7 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 actual operators, making it difficult to create sounds ‘from scratch’! But Yamaha knew how to please the majority of customers — the machine came with an extensive range of preset sounds. It also accepted RAM and ROM cartridges which expanded the choice still further.
A huge number of digital machines, often using highly innovative ideas, have followed — but perhaps the greatest advances should be in ease of use!
Sampling
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The Roland S-50, with its provision for VDU, was a pioneering keyboard machine that stored samples on diskette. It was followed by the rack-mounted S-550 which provided multiple outputs. But the ‘industry standard’ for many years in the world of sampling was the Akai S-1000.
A new generation of machines has since appeared, with samples that match the quality of real digital recordings. They include the E-mu Proteus and Procussion — both playback only samplers which contain a vast repertoire of instruments, demonstrating a high technical quality coupled with sampling artistry. Moreover they are capable of exploiting MIDI to the full — they can play 16 sounds, each with 16 note polyphony, at any one time.
