The Fairlight Explained (Part 9)
Delving ever further into the Computer Musical Instrument from down-under, Jim Grant samples the delights of Page 9's real-time sequencer.
We leave the realms of sound-generation and turn our attention to the CMI's other great compositional asset: its versatility as a music production tool.
This month sees us moving onto a different aspect of the Fairlight's abilities: that of music production. These days, there are all manner of instruments employing digital techniques for the creation of sound, but few if any offer the comprehensive music-making facilities, both real and non real time, that the CMI has as standard.
The most obvious means of music input is of course via the music keyboard; Page 9, the keyboard sequencer, is shown in Figure 1. At first sight, this seems a little complicated, especially since all you expect it to do is to remember the notes played and their duration. But this is where the genius of the Fairlight really shines through. It is, after all, a powerful microcomputer with large secondary storage in the form of disks. (Or is it a musical instrument masquerading as a computer? I guess the answer to that depends on whether you're repairing it or playing it.)
To record a music sequence, the CMI opens a file on the user disk with the name specified in the Record File area. It automatically suffixes the letters SQ after the name, to distinguish it between voice (.VC), control (.CO) and instrument (.IN) files.
Once the Record command is given, the CMI begins building a file in RAM with the information received from the music keyboard. Remember that the Fairlight is a distributed processor system and that both the music and alphanumeric keyboards contain micros of the 6800 family doing all the work. Normally, the music keyboard acts as a host for the alphanumeric data, and passes both it and the music information at 9600 baud to the CPU. But just in case of confusion, differences between ASCII text and keyboard notes and velocities are highlighted by a flag contained in the data. On receipt of the serial data stream, the CMI sorts out the source and stores the music information in RAM.
All of this takes place unseen by the musician, and quite rightly so, but here's the clever bit. Most digital instruments have a limited amount of RAM that can be released for sequence information, something that's soon consumed whenever the user attempts layering complex polyphonic music. The CMI not only has double-sided disks to store information, it also uses Page 9 software to dedicate Processor 2 in the CPU to detect when the note buffer (built by Processor 1) is half-full and then write the sequence data to disk, emptying the buffer as it does. The upshot of all this is that you can play away to your heart's content, in the certain knowledge that the memory represented by the disks amounts to a total of more than 50,000 notes. It's for this reason that the size of a Page 9 sequence is unknown when they're first opened. And while recording is in progress, the file is dynamic and grabs as much space as it needs until the Stop command is given.
In Replay mode, Processor 2 reopens the sequence file and reads a chunk of it into RAM. Processor 1 acts upon the data and generates the notes and timing information, subsequently passing them to the channel cards. Again, when the buffer is half-empty, Processor 2 gets a signal and reads in the next block of data while Processor 1 carries on with the business of playing music. It's all terribly clever, and, in fact, fascinating to watch the different processes come into play (no pun intended) as the music progresses.
Well, that's how it all works. How do you actually work with it? Recording and Replaying a file is simply a matter of specifying the name in the designated areas and hitting the displayed command with the lightpen. When the Stop command is given, the CMI closes the sequence file; if recording was in progress, it also updates the Free Space number shown in Figure 1.
The Replay Trim component is very much like the start and end leader on a reel of tape; Head Time is the time from the beginning of the sequence to the first event; and Tail Time is the time from the last event to the end of the sequence. These can be adjusted after the sequence was recorded, and saved with the file on disk.
A variation on the Replay command is the Repeat function. In this case, the head and tail times can be adjusted as the sequence is playing to obtain a smooth repeat.
Of course, it's often desirable to layer or multitrack sequences, and this can be done with the Merge command. Here, two named files must be specified with the Replay file (including the Repeat option) while a new Record file is built on disk containing information as played on the keyboard and the data from the Replay file.
But in addition to holding music information, the Record file can also act as a memory for control data generated by the three sliders, three footpedals and five switches that are associated with the Fairlight's music keyboard. This allows performance information such as swell, vibrato and so on to be sent to the disk along with the notes and their durations.
It's possible to mask the effects of these controls on both Record and Replay. This is particularly useful, as it allows you to Merge several pieces of music with the controls and switches off, and then create a final Merge file with the controls and/or switches adjusted to alter the sound. The movements are recorded on disk along with the previously-recorded music.
Time in the sequencer is measured in microbeats, and the Speed control defines the duration of a microbeat as a number of system clock cycles.
As you'll no doubt be aware, a good many digital musical instruments - especially drum machines and their ilk - have some means of synchronising their tempo with an external signal generated by another instrument. This is commonly a click or a sync tone, with the clicks being short voltage pulses which occur on every beat.
However, that sort of syncing system is now falling out of vogue, as it was originally conceived to replace the gate signal on voltage-controlled machines such as sequencers. Perhaps the method's single biggest disadvantage is that due to its low repetition rate, it can't be recorded directly onto audio tape.
The cure to all this is the sync tone, a pulse train whose frequency is related to the number of beats per minute being output by the machine(s) in question. This makes it suitable for recording directly, as the number of pulses per beat is usually between 12 and 96.
After all that, what do you know? The CMI doesn't even give a Sync Out pulse, since a sinusoidal voice can be pressed into service whenever required. It does, however, accept a Sync In signal. Figure 1 shows that internal microbeat drive is elected, but this can be changed to external (or EXT), enabling the CMI to count external sync pulses to drive the sequencer. A Click Out facility is also present, and this can be useful for providing a metronome beat if you're attempting to record a particularly difficult passage, for example.
The Keyboard Selection facility is related to Page 3, and Figure 2 shows an example of this just to jog your memory. If you remember, there are eight keyboard maps on the Fairlight, all of which the master and slave keyboards can be set to control.
Changing the numbers on Page 9 causes the selected keyboard to leap onto the chosen map displayed by Page 3. This is quite important, since if you think of Page 9 as an eight-track recorder, the keyboard number becomes the number of the track on which you're about to record.
The Fairlight calls its recording tracks Input Streams, and the table shown on Page 9 (Figure 1) allows you to govern which stream will play which keyboard in Replay mode. Remember, Page 9 records key events, not sounds, so you can dynamically swap the mapping of music to sounds during a piece by changing the stream-to-keyboard allocation.
But imagine an eight-track tape recorder with an individual instrument recorded onto each separate track. Naturally, the sound of each instrument is bound in separately to the music laid down on its particular track. Not so with the Fairlight. By changing the input stream-to-keyboard number, you can use the music recorded on Track 1, say, to play the sound associated with Track 5. During a Merge, this dynamic allocation of streams can be turned off simply by assigning it to a fictitious Keyboard 0. It sounds like cheating, but it's helpful nonetheless...
That about wraps it up for Page 9. It's a powerful and flexible recording tool that was an awful long way ahead of its time when it first appeared a few years back. It has only one problem. It's easy to use if, and only if, you have a reasonable amount of keyboard-playing skill. If you haven't... well, maybe you'd better wait for next month's Fairlight Explained instalment.
Feature by Jim Grant
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