Continuing the extensive guide to the many micros available
(currently £45 inclusive of 16K RAM pack)
A casual look inside the ZX81's casing will soon show that Sir Clive had something other than sound on his mind when putting together this wedge of plastic and silicon - not a piezo transducer or speaker in sight. So, as the ZX81 stands, it's as silent as the grave, and just about as appetising when it comes to making music on it. That said, there's a fair range of add-ons and software designed for squeezing sounds out of the machine.
If your aim is to turn the ZX81 into something that's more like a musically useful sequencer, then your best bet is probably to have a look at the series of articles that ran in the Dec '81 to Mar '82 issues of E&MM, under the heading of 'Micromusic'. These describe the construction and programming of a polyphonic sequencer using an additional input/output port (capable of driving Wasps and Gnats directly) together with the option of DACs (if you're intending to use 1 volt/octave synths). Peter Kershaw's software can cope with seven monophonic synthesizers, each with up to 1825 events, and makes for a reasonably straightforward system of music entry. That's the good news. The bad news is that no PCBs were ever designed for the project, so it's over to wire-wrapping and Veroboard this time round. The other problem is that the Wasp has its sustain disabled when interfacing via the link socket. Still, if you're after a cheap 12,000 note polyphonic sequencer, you can't expect to get the earth for peanuts...
In 'Rumblings' last month, I made some noises about the AMICS system being developed around the ZX81, also aimed at running EDP synths on the cheap. Unfortunately, those plans have been somewhat squashed by the apparently impossible task of getting the ZX81 to accept Z-80 machine code downloaded from an Apple. Yet more ULAs turning into UFOs. So, the long and the short of the story is that the system will instead be based around the Spectrum, a move that'll be greeted with a huge sigh of relief from all that value their sanity. Mind you, if anyone has been able to successfully turn their ZX81 into a dedicated music processor, we'd like to hear from you - offers of riches galore, untold glories, and all that sort of thing.
The really interesting thing about the Jupiter Ace is the fact that it runs in FORTH. The beauty of this language is that it is 'threaded', ie. a 'kernal' FORTH word becomes the subject of discussion of another word, which, in turn, donates itself to a further word, and so on and so forth (aargh ...). A bit like the dietary habits of fishes, really. As an example, let's define the word STARS:
|: STARS||(: starts word definition)|
|."***"||(print three asterisks)|
|200 100 BEEP||(play a note of pitch value 200 for 100 ms)|
|;||(; ends word definition)|
The Spectrum is a regular occupant of the Number 1 position of the micros sales chart, and rightly so, because it's a terrific machine for games and other popular applications. What it lacks in the sound and keyboard department can be improved upon by adding the usual array of Sinclair addons, though you may feel somewhat cheated once your cheap 48K machine has zoomed over the magical £200 mark. Still, it does have good colour graphics, a reasonable (if idiosyncratic) version of BASIC, the Design Council's stamp of approval, the microdrive, and loads and loads of software (including a small number that are musically oriented).
Like the Jupiter Ace, the Spectrum is a single-command micro when it comes to music - another BEEPer, in fact. In theory, the Spectrum BEEP has a range of 18 octaves, from 8.17Hz to 14,080 Hz, a piece of info which is of dubious value considering that Spectrum BASIC limits the pitch range to 130 semitones. But unlike the Jupiter Ace's BEEPing FORTH, the Spectrum goes along with the usual convention of putting the parameters, duration (in seconds) and pitch (+ ve and - ve semitone offsets away from middle C), after the command. Also, Spectrum BASIC has a PAUSE command, which allows some more-or-less subtle delay to be added between notes. So, putting these snippets together gives us a typically tedious and unmusical rendition of a million-dollar tune:
10 FOR I = 1TO5
20 READ P
30 BEEP 0.5,P
40 PAUSE 250
60 DATA 21,23,19,7,14
Well, it could be worse. At least the Spectrum designers have provided the option of directing the BEEP to an external amplifier via the cassette mic socket, which offers a vast improvement over the wretched piezo. In fact, played through a decent sound system with some echo and chorusing, it's of surprisingly good quality - albeit a square wave. One major problem with the musical side (joke) of Spectrum BASIC is that the program actually stops while BEEP is doing its thing, which means that ambitious programming attempts aimed at turning the 'qwerty' keyboard into something vaguely reminiscent of a synth have a habit of coming unstuck. In short, programs have to be written so that each note is either a predetermined length or a sequence of very short notes played in a stuttering Stylophone fashion.
As with its little brother, there's a fair range of software covering both software-only and hardware-assisted music making.
HARDWARE: Here, there's a choice between the sort of hardware that just amplifies the basic sound output from the mic socket, and that which drags another GI sound chip into service. Frankly, I can't see the point of adding on another amplifier and speaker of doubtful quality if you've got anything like a Hi-Fi system to hand, but I guess that some users might be adequately titillated by hearing a poor sound a bit louder and a bit better. If that's the case, then the Spectrum Sound Amplifier (£7.75, from Fuller Micro Systems, (Contact Details)) should do quite nicely.
However, a greater chance of guaranteed aural satisfaction is likely to be achieved with one of the sound chip add-ons. For instance, there's the simply named 'Addon', which packs the usual 4 sound channels, 3 joystick ports plus the amplification of the standard output into the same box-on-the-back, and at a reasonable price (£20.50, from Micro Power, (Contact Details)).
Other possibilities include the Fuller Sound Box (£30.75, from Fuller Micro Systems, (Contact Details)), which uses the GI AY-3-8912 chip and provides a single joystick port and the Zon X (see ZX81). However, using the latter on the Spectrum also necessitates an extra outlay in the shape of a special Spectrum extension board (£6.80, address as above in ZX81 section). That's because the Spectrum edge connector doesn't give access to any sort of clock, and so an external crystal is needed to generate the sort of clock signal that's necessary to get the sound chip generating away.
SOFTWARE: Not an amazing array of commercial goodies, but there are a few worth having a look at. One of the few treading the CAI boards is Note Invaders (£9.25, from Chalksoft, (Contact Details)), this includes programs for note recognition in both a traditional and a frantic games format (naming notes before you're blasted from the sky - or something along those lines). This software is also available for the BBC Micro and the VIC-20. Another bit of software using the basic capabilities of the machine is Composer (£5.95, from Contrast Software, (Contact Details)). This is fairly basic (a simple sort of 200-note sequencer), but it does have good editing facilities. On the sound FX side, there's a utility program called White Noise & Graphics (£5.95, from Gilsoft, (Contact Details)), which adds various commands to BASIC, including those for explosion-type sound FX.
Another possibility is simply called Sound FX (£5.50, from DX Tronics, (Contact Details)), but I haven't a clue what it actually does.
Frankly (and this isn't blowing one's own trumpet), the more than casual musical user of the Spectrum would probably do well to look at the various Spectrum articles that have appeared in E&MM over the last year. Starting off with the basic machine, there's the Beepquencer that appeared under the banner of 'Micromusic' in the Oct '82 issue. Basically, this is a sequencer which allows you to enter up to 16 repeating tunes, each with up to 32 notes over a range of 4 octaves, complete with cassette save and load facilities. Next on the list is the Spectrum Synth Controller, which materialised in the Nov '82 issue. This is similar in operation to its basic predecessor, but uses some extra hardware (an I/O port plus a CV-producing DAC) to drive any standard analogue synth. The main drawback to this project is that no PCB was designed, so I'm afraid it's back to the old veroboard and smouldering iron.
A more ambitious (and interesting) project is the OMDAC (June '83). This is a general-purpose module for interfacing a micro with up to 8 synths, and also provides in and out control lines (suitable for drum syncs et al.) and an ADC for reading in potentiometer settings and the like. Though the original design centred around using it with the Acorn Atom and Spectrum, there's no reason why it shouldn't be used with any 8-bit micro, including the BBC Micro, Commodore 64, or Apple. The other good news is that a PCB is available (£5.95, direct from E&MM). The bad news is that there is not much in the way of software available yet. However, there must be a market for a cheap polyphonic sequencer to control all the sundry analogue synths that musicians have a habit of accumulating over the years, so we'll move hell and high water to get some sort of software development program under way.
Finally, there's the intriguing area of the MIDI, the Musical Instrument Digital Interface that the majority of synthesizer manufacturers have agreed upon. It's early days to foresee precisely how earth-shattering this development will be, but one thing that's clear is that musicians may not take too kindly to being asked to part with a large amount of cash for an extra micro and all its attendant peripherals on top of the MIDI synth itself. That's where a cheap (but good) micro like the Spectrum can step in with a vengeance, and, with the advent of the microdrive, it becomes an even more sensible proposition as a MIDI micro. The May '83 issue of E&MM includes the majority of the available info on the MIDI in one article and a hardware design for a Spectrum MIDI board in another. The PCB for this is available directly from E&MM (for £4.25), but a ready-made board may also be available sometime in the future. As with the OMDAC, home-grown software is at a rather early stage of development (the Prophet 600 MIDI-dump program in the August '83 issue, for instance) and any programming ideas or complete programs are likely to be received with open arms by E&MM!
Feature by David Ellis
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