The Fairlight Explained (Part 2)
Second instalment of Jim Grant's five-year mission into the unknown, or what goes on inside the world's most popular computer music tool.
The second part of our insight into one of the world's most popular computer instruments looks at display pages and what they tell CMI owners.
Last month we described the general software concept of the Fairlight and how much of its power lies in its ability to present its functions to the user as a group of related files called Pages. We saw that the CMI powered up with the Index Page (Page 1) and that sound and music files were managed by Page 2.
One of the problems associated with most sound-generating equipment is the way in which the sense sight is excluded from the process of sound formation. Most instruments operate on the basis of the user twiddling the controls and stabbing the keyboard. Fair enough: of all our senses, the ears are by far the most acute. Yet if we consider all the electronic music equipment currently available, the most user-friendly instruments have graphic displays, perhaps in the form of panel legends and LEDs or liquid crystal display. Despite the fact that sight is a very poor qualitative sense, it can be of enormous psychological help in our field. Basically it boils down to: 'If I can see it, I can understand it.'
There's no doubt that the Fairlight's visual presentation is founded on this premise. Each display Page is graphic without being ostentatious, and Page D, the voice waveform display, is a prime example of this. Typing PD followed by a RETURN on the alphanumeric keyboard will result in a display of the type shown in Figure 1. To appreciate the significance of the display, we must delve a little deeper into the workings of the CMI.
Remember that voice information is held in 16K of RAM on each channel card. To simplify matters, the CMI divides the memory (and thus the waveform) into 128 sections called segments. Each segment consists of 128 bytes, so the waveform comprises 128 segments multiplied by 128 bytes to give 16384 bytes, ie. 16K. This saves the musician handling unwieldy computer numbers when dealing with the waveform RAM.
The display shown in Figure 1 is a pseudo-3D representation of the voice called TRUMPET. Each line from left to right is a segment, and the foremost segment represents the beginning of the sound. When a keyboard note is pressed, the CMI reads out the RAM information segment by segment from the front to the rear of the display.
There are two display formats, A and B, and a number of options within each type. Figure 1 is in format A, and segments 1 to 128 are shown in steps of 4. Figure 2 is again format A, with the end segment number 32 and steps of 8: therefore only five segments are shown. Format B gives an oscilloscope-type display, but with each segment slightly above the preceding one. Again, there are a number of display options. Figure 3 shows TRUMPET segments 1 to 128 in steps of 2, and Figure 4 segments 1 to 64 in steps of 8.
Although Page D is purely for display purposes and does not support any sound creation commands, it's still an invaluable aid. At its most basic level, it answers the questions 'where has the sound gone?' and 'is the waveform zero?'.
Page 3 is another utility-type display Page. It deals with voice tunings, Channel allocation and keyboard maps.
Figure 5 shows a typical display with eight separate voices loaded into the CMI. Registers A to H are groups of one or more of the eight Channels and 'NPHONY' is the number of notes that can be played with the sound held in a Register. A quick look at Figure 5 reveals that there are eight active Registers, each holding the voice indicated. In this case, all eight Channel cards hold a unique sound, and therefore the maximum number of notes that can be played on the keyboard with any single sound is one. This is indicated by the corresponding 'NPHONY'. If a single eight-note polyphonic voice is required, only Register A will be active and Channels 1 to 8 will be allocated to A. The active Registers are mirrored on Page 2 so that they can be loaded with sounds from disk. The Fairlight will flag an error message if you try to open another Register or increase the NPHONY beyond eight. A simple rule applies: the sum of the active Registers times their NPHONY must be less than or equal to eight.
Figure 6 shows another example of the Register allocations. Here, another set of voices has been loaded, so the NPHONY and Registers are configured differently. Although the Register and NPHONY settings may seem a little confusing and limited, the exact configuration is determined entirely by the musician, and changes can be effected very quickly for evaluation.
Any voice can be tuned in increments of plus or minus one hundredth of a semitone up to ±6 octaves with crystal accuracy. Scale allows the Western tempered tuning of 12th root of 2.00 to be changed to any other macro/micro tuning, eg. for quarter tones, you simply change Scale to 24th root of 2.00. Pitch is a master tuning control which can vary tuning of all the loaded voices by a quarter of a tone in 256 discrete steps, to bring the CMI in tune with other instruments if necessary.
The Keyboard Maps each consist of a keyboard number (1 to 6) followed by six letters indicating the Register assigned to each octave. As the CMI is a musician's instrument, it supports two six-octave keyboards called the Master and the Slave. Using the maps, it's possible to create eight different keyboard configurations by choosing which sounds will play on each octave within a keyboard. The Master and Slave can be linked (as shown in Figures 5 and 6) to any map by changing the Selection numbers.
The information presented in Page 3 is known as an Instrument file. The file can be saved on the user disk and is given the suffix NAME.IN. When this file is loaded it will pull the specified voices into the CMI, allocate the Registers automatically, adjust the tuning and spread the sounds across the keyboards. Instrument files are a usefully quick way of bringing the CMI up to a playable state with 'preset' voices and tuning.
At the time the Fairlight was designed, the microprocessor was considered to be a medium- to slow-speed device. To increase the power of any computing system, designers have two basic choices.
One of these (the Synclavier approach) is to base the instrument around a discrete logic minicomputer, thus utilising the raw speed of logic chips. This is quite an elegant solution since 'music by numbers' requires lots of number crunching, but the other choice, and one which is becoming increasingly popular, is computing concurrency. In a basic CMI system, there are four microprocessors of the 6800 family. Two of these are in peripherals, ie. one each in the music keyboard and the alphanumeric keyboard, and this means there can be several independent processes being executed concurrently.
The microprocessor in the alphanumeric scans the keys and passes the data to the music keyboard when requested. At the same time, the music keyboards are scanned for pressed notes, key velocities are calculated, and the control sliders and switches read.
At the right-hand end of the Master keyboard is a calculator-style keypad and alphanumeric display used for rapid loading of voices in a live situation. Music keyboard information has the highest priority of all data in the CMI, which responds instantly to the packets of data sent flying down the cables at 9600 Baud.
Well that about finishes off our description of the utility-type display Pages. In case you're wondering what the Mode setting on Page 3 is for, don't worry: all will be explained.
Next month, the controls on Page 7 and sampling on Page 8.
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