When a CMI page is as helpful a source of music graphics as Page 6, you can bet your life it needs a lot of explaining - so this month's episode is dedicated entirely to it.

If you're trying to create a new sound on the Fairlight, whether it's from existing sampled data using Page 8 or harmonic profiles generated on Pages 4 and 5, you can be sure that Page 6 will be referred to over and over again.

At its simplest level, Page 6 is a static 'oscilloscope' containing one segment of the waveform RAM. Like Page 4, the large black area is a reverse video image and represents the region that can be hit by the now-infamous lightpen. But unlike an oscilloscope, which acts only like a window on the information, Page 6, in conjunction with its commands and light-pen, behaves more like a door through which we can directly access the waveform data.

The Manual Approach

Regular readers of this series will probably recall that each segment consists of 128 bytes, and that each byte can hold a range of values from -128 to 127, giving a grand total of 256 possible values. Now, we can highlight any particular byte by positioning a narrow vertical window over the display area. The byte in question, shown in Figure 1, has its position indicated by POINT and its value by LEVEL: these can be changed by typing in different values from the alphanumeric keyboard. So, theoretically at least, you could type in 128 levels for each byte shown in Page 6, and repeat the process for all 128 Page 6 displays to cover the entire sound, giving 16,384 levels in all. In practice though, such a feat would take an unbelievable amount of manual labour (exactly what much of the Fairlight's software was designed to eliminate) to achieve, and this has led me to wonder whether this feature will be dropped when the Series III Fairlight, complete with waveform RAM of megabyte dimensions, makes its appearance later this year.

A more practical approach is, of course, to make use of the lightpen. This is as simple as drawing on the back of a bus ticket, but just in case even that is beyond the user's artistic capabilities, the JOIN and PLOT functions also present on Page 4 are available here, too, to help out with the drawing of geometric shapes.

In fact, trying out a few sample sketches soon reveals that waveforms which look drastically different may sound surprisingly similar. Scientifically speaking, this is probably due to the fact that as a species, we have little prior experience gained from our senses that relates visual time domain waveforms to what we perceive in terms of harmonics or partial.

But Page 6 waveform-drawing is of enormous help, first because it gives the user extensive and direct control of waveform RAM with one sweep of the hand, and second because the ability to bring about such drastic sonic change so simply and visually (almost artistically, some might say) is a practicality light years away from the sophistication and complexity of the underlying machine and its software. Or to put it another way, it makes the CMI seem less of a beast and more of a pet.

The Practical Approach

Alteration of the display image is not reflected in the waveform RAM until the FILL command is used. This allows the reverse video field to be used as a scratchpad area in which waveshapes can be developed before they are finally committed to RAM.

Looking again at Figure 1, notice there are two 'slider' controls similar to those on Page 5. These control the segment number to be displayed and the stepping rate through the entire memory instigated when the command Step is issued. Also shown are three classic waveforms - triangle, sawtooth, and square - which deposit a perfectly fitting single cycle wave into the segment. The pulse width of the square can be varied from 1 % to 99% by changing the value held next to the square wave symbol.

Auxiliary Commands

In addition to the graphic capabilities of Page 6, there are a number of commands that can only be entered from the Fairlight's alphanumeric keyboard. Figure 2 shows the range of functions available, as presented by the HELP sheet menu.

First off are a few utility-type commands. GAIN scales the displayed data by a specified percentage: if the rescaled waveform is about to exceed the amplitude range of the system, the CMI will ask you whether or not you want to proceed and thereby induce clipping. If you reply in the affirmative, the command will be duly executed. Meanwhile, the INVERT command inverts the phase of the waveform: this is useful as a prelude to some of the other functions such as MIX, MERGE and ADD.

A particularly neat little command is ZERO, which allows us to create a null voice in preparation for the ADD command. The entire waveform RAM can be turned end on end by using REVERSE, and this results in the backwards sounds that have become familiar to pop music followers the world over.

REFLECT is a less commonly-used but if anything more interesting variation on this theme. It allows us to place an imaginary mirror in the sound and reflect every part of the waveform in front of this mirror to waveform RAM behind it. Take a look at Figures 3 and 4 for before and after views: the 'mirror' is at segment 64.

Now on to another of the seemingly insurmountable problems brought on by the onset of new musical technology. Very often, when a sound has been sampled, the beginning of the captured data does not occur at exactly the start of the RAM, perhaps due to some extraneous noise pretriggering the ADC. However, if the effect isn't too severe, a convenient method of correction is to ROTATE the sound within the waveform RAM to bring the start in line with byte 1. This has the (often desirable) side-effect of shifting the first part of RAM to the end. See Figures 5 and 3 for another revealing before and after picture.

I imagine NOISE will be fairly self-explanatory to even the least clued-up of this column's readers: it fills sections of the RAM with the output of a random number generator hidden inside the software. Funnily enough, the GAIN command is also used to tailor the amplitude of the noise to that of the rest of the sound...

Now, BLEND is a strangely out of place command. Personally, I think it should be on Page 4, since its role is to help smooth out glitches caused by imperfect looping points. It may be that to find a good loop it makes extensive use of extrapolation techniques, and that seeing as this is a central feature of the MIX and MERGE commands, Fairlight decided to bung it on Page 6 alongside them.

However, rather than discuss the remaining Page 6 commands in any detail right now, I think it's probably best for all concerned if I demonstrate their power in the context of a typical edit session in which a sound is created from scratch, ie. without any sampled data. So, now you know what I'll be talking about next month.