SIMON N GOODWIN finds another fine disk interface in MGT’s Plus D and gets rhythm with the SpecDrum System Two
IF YOU’RE planning to upgrade your Spectrum, the new Plus D interface from Miles Gordon Technology — MGT — is definitely worth a look. It’s well-designed and amazing value for money.
For £50 you get a disk interface, parallel printer port, sophisticated software to control both these, and a simple snapshot device that lets you print screens or save programs of any size to disk.
A 780K 3.5-inch disk drive costs an extra £80 if you buy it at the same time as the interface. You can use any standard 40-track or 80-track drive, but you’d have to be very well-connected to beat the price of the MGT drive.
The Plus D was designed by Bruce Gordon, who invented the popular Disciple interface two years ago. That was a competitor for the grandfather of all Spectrum interfaces, Sinclair’s aptly-named Interface One. The £90 Disciple is still available from Rockfort Products.
The Plus D might be viewed as a cut-down version of the Disciple. but that would be unjust. The Plus D is a complete, coherent product. It lacks the Disciple’s through-port, joystick and network connections, but still works with the many programs that have been converted to use the Disciple’s disk and printer interfaces.
£49.95 buys you a plain black metal box, not much bigger than a single cassette case. An edge connector protrudes from one end of the box, and plugs into the back of your computer. Two IDC (bed-of-nails) sockets are flush with the other end of the box: one connects to the printer, the other to one or two disk drives. A red light and a small reassuringly rubbery button garnish the top of the box. That’s it.
The Plus D fits any type of Spectrum, as it pokes out from the back of the computer rather than vertically upwards. You need about 12cm of clearance at the back of the computer: it’s best not to use the legs at the back of a Spectrum or 128K, as they would leave the Plus D hanging precariously by its connections.
The metal box isn’t just there to make the unit feel chunky — it also acts as a heat sink, keeping the Plus D cool and shielding it from radiated interference.
Inside, there’s a neat double-sided circuit board holding a custom PAL chip, a standard 1772 disk controller, 8K of ROM and 8K of RAM, a latch for data being sent to the printer, and eight ‘glue’ chips to tie the rest together. Two of these chips have been soldered piggy-bank style on top of other components — this looks ugly but shouldn’t cause any problems.
The RAM holds part of the disk-control and printer-control code, and is loaded from disk or cassette when you turn on the system and type RUN. This arrangement makes the Plus D flexible, though arguably it’s unnecessary. You don’t need to reload after a reset, unless the system has crashed or been turned off since the last load. Clever hackers can even run short routines in the Plus D’s internal memory without disturbing the main programs.
The Plus D comes with two A5 leaflets — a user’s manual and a ‘free introductory issue’ of FORMAT, the magazine of the Disciple and Plus D users’ group. The main manual is 24 pages of daisywheel type, stuffed with useful information, readable but very dense. There’s no index.
This manual is filled with useful practical tips that stem from experience, but it does not document the Plus D completely — some of the error messages are not listed, and several technical features are only mentioned in passing. It’s a good manual, but would nevertheless benefit from a rewrite.
The magazine FORMAT is a gas, with a great mixture of technical articles, advice and gossip. Subscriptions cost £10 a year, and if I were buying a Plus D as a present I’d be sure to include a subscription. User groups like this one make the purchase of add-ons fun, rather than a risk.
When you first get your Plus D you must load a cassette to tell the interface about your set-up. The program loads after about three minutes, displays a neat animated screen and BEEPS out Cliff Richard’s sixties Eurovision hit Congratulations! Three tidy screens of text follow, and you’re then asked to specify the details of your disk drive and printer, in a nonthreatening question-and-answer sequence.
There are some memorable printer options, like a facility to print Spectrum user-defined and block graphics. There’s a fast screen COPY option, and a slower shaded printout. The program initially assumes you’ve got an Epson printer; it’s easy to customise the control codes sent, as long as you’ve got something similar and can find your way around its manual.
When all the questions have been answered you are invited to put a blank disk in the drive so that the machine can format it and stash away the system details. After making extremely sure you’ve put the right disk in, the little light on top of the Plus D goes out, to show that the disk is busy. It takes about a minute and 40 seconds to initialise a 780K disk.
The easiest way to use the Plus D is via the magic button on the top. You can load games or other programs as normal, and then press the button at the point at which you want to SAVE them. The button freezes the program temporarily and fills the border with a pattern, while the system waits for you to press a key.
The digits 1 and 2 print the screen out, in either format. Key 3 saves the screen as a disk file. 4 saves an entire 48K program, including the screen. 5 saves 128K, and X restarts the program.
This snapshot mode is relatively simple. You can’t choose file names, enter POKEs or check if a disk is full. Beware, even if you think there’s enough free storage to hold a program — the Plus D can fit no more than 80 files on a disk, and if this limit is exceeded attempts to save will fail and give no message.
When saving a 128K program, you must tell the interface which of the two possible screen displays the program was using, so the right one is picked when the snapshot reloads. If the picture changes part way through the SAVE, you must enter Y to tell the Plus D to choose the other screen; otherwise, type N.
The manual says that a 48K program saves in ‘just over three seconds’ — in fact I measured the time, including a period of directory-searching that precedes most file actions, at about eight seconds, or 16 for a 128K file. Loading takes about half this time. Speeds vary a bit depending upon your drive and what’s already on the disk, but Plus D Snapshots should be fast enough for almost anyone!
Snapshot files are not compressed as they would be by the Multiface, but you can still fit 18 48K snapshots, or six 128K ones, on a single disk. I couldn’t find any programs that could not be saved at the press of the button, but programmers and hardware designers compete constantly in this area, so there are probably one or two resistant games around.
The Plus D is fairly compatible with programs designed to work with microdrives. It recognises the same BASIC commands as Sinclair’s Interface 1 and also handles the hook codes that machine-code programmers are supposed to use.
Sadly Sinclair made rather a mess of these codes, so many existing programs jump straight into the microdrive code. This works OK with Interface I, or with a Swift Disc as long as you’ve got their Emulator loaded so the disk code mimics the microdrive very accurately. Unfortunately such jumps usually crash the Plus D.
Beta BASIC and all the HiSoft compilers are among the programs which work without problems, I found that Laser Genius and Cheetah’s Sound Sampler were painlessly converted to run from disk by their microdrive loaders, but the sound Sampler couldn’t LOAD or SAVE to disk. Laser Genius would SAVE and LOAD files, but the CAT command crashed the system, as did references to microdrive 2.
If you want to use software designed to work from microdrive with a Plus D you ought to ask MGT or the user group about it first.
The Plus D recognises Interface 1 commands, and many useful variations of its own. It allows microdrive syntax, to suit existing microdrives and the Plus D at the same time. Alternatively, you can use MGT’s own simplified syntax.
LOAD and SAVE work with all the usual file types, and SAVE D1 "name1" TO D1 "name2" lets you copy files around a disk, or from one drive to another. Unfortunately this won’t copy snapshots or files created with the OPEN command. Copying is quite fast, even with a single drive, but it overwrites the program in memory, so you should SAVE that first.
There are two types of CATalogue: one lists disk filenames in three columns, while the other gives full details of each file, including its number, size and location, line by line.
If you’re after a quick getaway you can load any snapshot by just typing LOAD, followed by P, followed by the catalogue number of the file. This trick doesn’t work for ERASE, the command to delete a file, because that would make it too easy to delete a file by accident.
You don’t have to supply full filenames, even so. Most commands work with wild-card symbols — for instance, a question mark stands for any letter, and an asterisk stands for any sequence of characters. So ERASE D2 "Snap*" erases all the files with names starting ‘Snap’ on drive 2. This will include all the snapshot files, which are given arbitrary names when the system creates them. Later you should rename them with a command like ERASE D1 "SnapC1A" TO "TechTips"
OPEN and CLOSE set up files, accessed with PRINT and INPUT or INKEY$. The normal microdrive syntax is extended so you can explicitly say whether you want to read or write a file, but you can’t use random access to skip around a file at will unless you’re also using the latest version of Beta BASIC — a fine add-on for serious BASIC programmers, but £16 extra.
As compensation, everyone gets direct access to the disk surface, in 510-byte lumps, via the hacking commands LOAD @ and SAVE @. POKE @ commands let you change the system configuration as a BASIC program runs. LLIST and LPRINT send programs and data to the printer port of your choice, and SAVE SCREEN$ copies the display to the printer.
MOVE transfers data from one stream to another. 128 BASIC crashes if you try to MOVE a file to the screen, but 48K BASIC lets you MOVE data to any device.
At its £129.95 total price (including the 780K-capacity 3.5-inch disk drive), the Plus D system is strongly recommended to anyone frustrated by cassette loading. It’s even worth considering just as a printer interface, if there’s a possibility you’ll want disks in future.
Sixword’s £150 Swift Disc system (reviewed in CRASH Issue 44) is still competitive, particularly if you’re interested in upgrading from a microdrive system. Both the Swift and the Plus D have unique features, and they’re much closer in price than any competitors.
Amstrad’s Spectrum +3 has serious compatibility problems and needs a £45 Multiface 3 before it can even approximate to the performance of an older Spectrum with a third-party disk.
Post-Christmas trade rumour has it that the +2 sold quite well but the +3 bombed, in the absence of much software on the slow and pricy three-inch disk format. It won’t be surprising it there’s a further big cut in the price of the +3 soon, following the £50 cut to £199 in September. Even so, I don’t think it will tempt many people who already own Spectrums — in particular 128Ks — away from the Plus D or Swift systems, which are superior upgrades.
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 any time.
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 at each sound in turn, giving a less convincing effect.
The original SpecDrum softwae lets you string together drum patterns on the screen and replay them at any tempo. Alternatively, you can alter 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 software 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 a 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 program 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 recordings 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 gismo 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 a 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 ignores 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’s 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 moving 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 useful.
REVERSE 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 lead 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 serialise in these pages. But don’t expect me to stop now, just when things are getting interesting...