When the Fairlight CMI was released seven years ago, both the machine and its software represented a significant step forward in the application of computer technology to music. Today, the Fairlight is used in the making of popular music the world over, as well as performing an important role in the field of musical and technological education. Despite this, very few people are fully aware of what the CMI does and how it does it. Jim Grant, who's been working with one for a number of years at the London College of Furniture, has decided to rectify matters by writing a series dedicated to explaining the Fairlight's workings. Part one appears below.

Before the Fairlight's appearance, most computer music systems were the prerogative of mainframes and their contribution to the world of everyday music was slight. Kim Ryrie (the Fairlight's father) and his Australian colleagues soon changed all that, however and their invention is now used in almost every area of music production, to the extent that many people appreciate its sound without realising that they're listening to 'music by numbers'.

However, despite its widespread use, there are relatively few Fairlights in general circulation - less than 100 in the UK - and to see one in action at close quarters is a real treat. Herein lies the rationale for this series of articles. What does the Fairlight do? How does it do it? And what can the average musician do with it?

Hardware

To take delivery of a Fairlight leaves your bank balance empty and your living room full. The hardware consists of a Central Processor Unit (CPU), one - or optionally two - six-octave keyboards, a typewriter-style QWERTY keyboard, and a VDU with added lightpen. In addition, there are some long connecting leads, a Systems floppy disk drive and a box of disks containing library sounds.

Software

A foolproof system of connectors - and a quick glance at the manual on the part of the user - ensures that the Fairlight can be powered up in no more than five minutes. The VDU displays the expectant message 'CMI READY', while the CPU hums quietly: there are three fans pulling air through the innards, keeping 500 watts of power dissipation down to an acceptable temperature...

Inserting the Systems disk in the left-hand drive (Drive 0) results in a faint click as the stepper motors engage. The operating software is loaded as a series of 'fetches' - each section of program loaded pulls in the next section. When this process has been completed, the user is faced with the Index page. See Figure 1.

Here lies one of the Fairlight's most powerful features. The whole system is menu-driven and the different options correspond to different VDU displays and sets of commands which are entered from the alphanumeric keyboard. Each option is referred to as a Page. A Page has one or more files resident on the Systems disk which are loaded when the Page is selected. Page 1 is the Index Menu itself (Figure 1), while Page 2 manages the files stored on the disk in the right-hand drive (Drive 1). These files are user-created, and there are seven different types, as indicated by the suffix after the file name. These are as follows:

NAME.VC is a voice file occupying about 20kBytes. It holds waveform data (16K) and extra information regarding looping and so on.

NAME.CO holds control information such as portamento, vibrato frequency and depth.

NAME.IN configures the CMI to a particular instrument state. Voices are automatically loaded and spread across the keyboard.

NAME.SQ holds polyphonic keyboard sequencer information.

NAME.RS is a real time sequencer (Page R) file.

NAME.PX corresponds to a screen dump (Page S) to disk. This can be spooled later to a dot-matrix printer for hard copy.

NAME.PC, PT, SS are Music Composition Language (MCL) files. These are generated on Page C and hold text files that describe notes with duration, dynamics and so on.

A voice file can be loaded in a number of ways. Probably the easiest is to point the lightpen at the voice name and then at the command LOAD at the bottom of the display (Figure 2). Drive 1 springs into action immediately, and after a second or two the selected voice appears on the keyboard.

So far so good. But where does the voice information go, and how does it result in a sound when the keyboard is played?

Channel Cards

Inside the Fairlight, there are usually at least 16 circuit cards, the exact number depending on various options such as an analogue interface and sync card, and eight of these are known as voice or channel cards.

The Fairlight produces sound by a process called Waveform Synthesis. Each command that deals directly with sound generation must involve at least a section of a waveform. The waveform itself is held in 16K of RAM on each channel card as a direct digital representation, so that increasing amplitudes give larger binary numbers. Therefore, when an eight-note polyphonic sound is present on the keyboard, each channel holds the same voice data.

Put simply, the channel cards can be regarded as digital oscillators whose waveform is determined by the contents of 16K of RAM (Figure 3). Different pitches - as played on the keyboard - correspond to the RAM information being read and converted by a DAC at different rates; the channel cards perform this function autonomously. The computer section of the Fairlight passes parameters such as pitch, vibrato, portamento rate and looping points along its data bus, and once these have been received, the channel card outputs the sound until the parameters are updated.

Overall pitching of the CMI is determined by a system clock resident on a special card known as the Master card. We'll be referring to this on numerous occasions over the next few months, since it holds the circuitry for a good many of the CMI's functions. A 34MHz oscillator is onboard, and this is divided and fed to the individual channel cards. It's from this clock that the RAM clocking rates - and thus keyboard pitches - are generated. The whole instrument can be tuned by scaling the master clock.

Page 2 Commands

Looking again at Figure 2, there are several commands at the bottom of the display. TRANSFER allows files to be copied from one disk to another, using Drive 0 as the destination drive. This is essential for creating backup copies of important music and/or sounds. DELETE erases unwanted files to make room on the disk. Invoking this command prompts a confirmation message to prevent accidental erasure of important files. When a file is deleted, FREE SPACE increases by the deleted file size.

At the very bottom of the display is an example of the QUERY command. This tells us that LOCUST.IN file will automatically load eight voices, whose names are shown.

Help Pages

By this time, you're probably wondering how anybody using a Fairlight ever manages to remember all the commands, especially since we've only considered Page 2 and there are another 13 still to go.

The answer is simple: Help Pages.

Figures 4 and 5 show examples of Page 2 Help Pages. In fact, the entire user's manual is held on the Systems disk, and sections relevant to the current display Page can be inspected at any time by typing HELP (what else?).

Initially, an index sheet is displayed (Figure 4). Touching any of the highlighted options with the lightpen results in the Help sheet specific to the selected option being loaded and displayed. The user can flick backwards (BWD), forwards (FWD), or recall a previous place (PRE): commands can be entered from the Help sheets while viewing their correct format. The CMI then automatically reloads the display page that called the Help sheet in the first place, and executes the command. And yes, there are even Help sheets that explain the use of the Help sheets...

That about wraps up the first part of what will doubtless become a saga of some duration. Next month, we'll take a look at Page 3 - the keyboard map - and the waveform display page, Page D.