CHEETAH'S SpecDrum package is one of the most versatile and successful add-ons you can get for the Spectrum, as more than 40,000 users have already discovered. Two years after the launch of the product it is still selling, and Cheetah has just released an add-on package, unimaginatively called the SpecDrum System Two, for owners of the original device.
The SpecDrum produces very authentic drum and rhythm sounds by replaying samples - large tables of numbers that describe sound waves - through a black box that plugs into the back of any Spectrum.
The principle is similar to that used in a compact-disc player, and though the SpecDrum isn't as accurate as a CD machine it's still a very convincing way to replay short percussive sounds under computer control. SpecDrum sounds have been heard on TV and radio programs, and even in adverts.
The basic SpecDrum costs £30 and consists of an interface to fit on the back of the computer, with a trailing phono lead to convey sounds to an amplifier. The cassette software lets you play around with a 'kit' of up to eight short sounds at a time; the sounds are arranged in three groups, and you can play any one sound from a group at anytime.
If you use sounds from several groups at once the SpecDrum automatically mixes the sounds together. Most other devices - notably the RAM Music Machine - play short snatches of each sound in turn, giving a less convincing effect.
The original SpecDrum software lets you string together drum patterns on the screen and replay them at any tempo. Alternatively, you can enter the rhythm for each drum individually, by tapping a computer key as the rest of the pattern plays.
The System Two will suit real drummers better as it lets you control all eight sounds directly from adjacent keys on the keyboard.
The main advantage of System Two over the original SpecDrum is that it allows more control over the drum sounds. You can tune them up and down in pitch by up to two octaves - the equivalent of a range of 49 notes on a piano. You can also play them backwards, or look at the graph of the sound and adjust the volume of the whole or any part. Thus you can make your own drum sounds subtle, distinctive or (with a bit of effort) both!
At first you can only edit and replay the eight sounds that are digitally recorded on the other side of the tape. The supplied samples include bass and snare drum sounds, electric and acoustic tom-toms, open and closed high hat cymbals, handclaps and a clave.
These raw recording use the maximum dynamic range of the system, so they can be tuned and edited with very little deterioration in quality. You can then assemble the sounds into kits that can be used with the standard SpecDrum program, mixing in original sounds if you wish.
To get best results from the System Two you need Cheetah's sound sampler - a £45 gizmo that lets you record your own sounds in the computer memory.
Much of the SpecDrum System Two software is devoted to sampling. The principle is the same as that for the Cheetah sound-sampler program, reviewed in CRASH last year, but System Two improves upon some of its best features and those of the RAM Music Machine software.
The main difficulty in recording good drum sounds at home is that the SpecDrum can only cope with very short noises; the longest sound it can handle is only about a sixth of a second. The System Two Sampler has the same restriction, and doesn't let you edit the desired part out of a longer recording, so it can take quite few tries to record a sound without losing the start or the end. Another display option, VIEW, shows you a solid graph of the whole recording till you release the V key.
The restricted sample length means that you can fit the program, a kit of eight sounds, and the drum pattern or sample being edited into 48K. Unlike the sound sampler's own software, but like the RAM Music Machine and the first SpecDrum program, System Two ignore the extra memory on a Spectrum 128.
It takes about 20 seconds to load or save a sample on cassette, and two minutes to save a complete kit of eight drums. Microdrive filing is supported, and I had no trouble loading and saving samples on the Swift Disk using Sixword's microdrive emulator; files loaded and saved in a few seconds, regardless of size. The program is supplied as a headerless tape file, so it is not easy to transfer it to disk without a magic-button device like a Multiface.
The System Two wave editor displays the detailed graph of a sample, spread over 12 display pages, with one dot representing the level of each individual sample. A recording is made up of 3072 separate sampled levels. You can move about in steps of half a page very quickly, and can position a cursor at any point on the wave.
You can edit the sample the hard way, by movinjg each dot on the graph. If you just want to adjust the level of all or part of a sample you can draw a line or ENVELOPE. The volume is automatically adjusted, throughout the sample, to correspond to the shape of the line.
TUNE lets you shift the pitch of the sample up or down by a semitone, over a range of plus or minus two octaves.
Reducing the pitch of a wave makes it longer; the extra information is lost.
The ENVELOPE and TUNE options degrade the quality of the recording slightly, but they're still useful.
REVERS turns the sample around so that it plays backwards. The CLIP option just cuts off troughs and peaks outside certain boundaries, generally causing distortion.
If you don't like the result of a change you can UNDO it to recover the previous sound. N and O play the 'new' and 'old' versions, so you can easily compare the sounds before and after editing.
In the last couple of years much space in this column has been devoted to editing and converting the sounds supplied with the original SpecDrum and Cheetah's follow-up cassette kits of prerecorded sounds.
The System Two lets you change the pitch of those sounds, but it will only let you adjust the volume of homemade samples and the eight sounds supplied with System Two.
Cheetah justifies this in the grounds that the kit sounds have already been balanced and attempts to change their volume may ;ead to extra noise or distortion.
The SpecDrum System Two works well and will be useful to keen SpecDrummers, but it is a shame that it has limitations that reduce the scope for experimentation (I hope to remove these in future CRASHes).
Still, it's a two-year old product, and the fact that it can be extended at all is a tribute to the original design.
If you already own the Cheetah sound sampler, the SpecDrum System Two is excellent value, and provides a much slicker link between the sampler and the SpecDrum than I have been able to serailise in these pages. But don't expect me to stop now, just when things are getting interesting...