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Enter the Compu-Music Age!

Now your home micro can become a complete musical band. We test the Amdek Compu Music system linked to the Sharp microcomputer.

The complete Sharp/Compu Music system.

The Roland Corporation's research with microprocessor based musical instruments has set its own innovative course of development with the early MC-8 Micro-Composer, followed by the MC-4 and synthesisers with digital oscillator control, such as the Juno 60 and Jupiter 8. With the Amdek Compu Music system, Roland have introduced a means of creative music making at low cost. The general concept of Compu Music is to allow musicians to use their existing home micro with the Amdek unit, CMU-800, to generate a fully polyphonic music score, complete with percussion rhythms if desired.

At the present time, the software has been prepared for three micros — the Apple II (using a disc based system), the Sharp MZ-80K (using cassette storage) and the NEC PC-8001. Both the Sharp MZ-80K and the Apple have their merits; the Sharp is considerably cheaper, whilst the Apple is being used with several makes of new instruments. Despite the very low price of the Amdek peripheral, it offers more facilities than currently available in one unique unit for micro control.

The sound sources for melody, bass, 4-note chords and 7 percussive sounds are generated in the Amdek unit, simply requiring an amplifier to complete the signal chain. In addition, control voltages and triggers for up to eight channels are available for driving 1 volt/octave synthesisers directly. To complement the well designed hardware, the software must be capable of adequately exploiting its potential, and here again the Amdek 'Soft-Package' is everything it should be: maximum user friendly, having minimum learning requirement, virtually crash proof, with music storage via cassette dump or disc boot.

No doubt the Roland research team collaborated with the sister Amdek company to impart some of their experience with the MicroComposers, as much of the MC-4 format is utilised. There is a possible added advantage that the VDU display offers — of analysing complete (screen) pages of music an instrument at a time. All that is required to connect the CMU-800 to a micro is a small interface accessory that has the necessary routing of signals to your micro's bus lines. Eventually, we should see many popular micros supplied with a suitable interface together with its software package.

E&MM are also researching the possibility of using the MZ-80A in place of the MZ-80K. Details will be published shortly. I am informed by Roland (UK) that variations in the software presentation may appear on other micros e.g. the Apple II, and it's quite likely that in a few months the name of Amdek will be changed for Roland on this and other products.

Amdek Compu Music CMU-800.

Setting up the System

Like most micros, the Sharp MZ-80K has a main bus output with address, data and special command lines. Normally this feeds to an interface unit that in turn allows connection of a printer, dual disc drive and other peripherals. The Amdek CMU-800 has a built-in ribbon cable that plugs directly into the supplied interface for the Sharp (IF-80C), and the ribbon cable attached to the latter plugs into the main bus socket at the rear of the micro.

When using the internally generated sound sources, 5 standard sockets offer a choice of a mono Mixed line output, plus separate Melody, Bass, Chord and Rhythm outputs for use with a mixer or tape recorder. Five sliders provide volume control of each output.

Each of the parts are termed 'channels', so we have Channel 0 = Percussion Rhythm patterns, Channel 1 = Melody, Channel 2 = Bass, Channel 3, 4, 5 and 6 = the Independently programmed lines making up the 4-note chord, Channel 7 = Extra external CV + trigger output, Channel 8 = Second extra external CV + trigger output, with portamento control. Channel 9 provides a storage area for putting rhythm patterns created in Channel 0 in the correct order for your piece of music. Channels 1 to 6 also have alternative CV and trigger outputs. The 8 channels in all increase the scope of the Amdek system immensely, as your own 1 volt/octave synths (or Yamaha/early Korg synths via Korg MS-02 interface) can be connected and running alongside the internal sound sources! Further refinements exist — more of which later.

Other controls on the main panel are Melody 'sustain' and 'decay', Bass 'decay', Chord 'decay' that allow slight adjustment of gate times you've programmed. There's also a 'tempo' control that runs the completed piece over a wide range of speeds. In other words, the software in the MZ-80K receives interrupts from an oscillator in the CMU-800. If you prefer, a Clock In socket enables you to drive the whole system from an external source. For example, the E&MM Synclock is suitable or the E&MM MF1 Sync Unit (for tape recording sync). A Clock Out socket lets you synchronise another Amdek unit or sequencer.


Don't let the heading put you off — you can't build the Compu Music unit yourself! Having become convinced by all the publicity that the Amdek name stands for 'music kits', you'll now have to get used to another sphere of ready-made computer peripheral products (see last issue for further details).

The CMU-800 all metal case is extremely compact, with a smart sloping front in light beige with dark grey legending secured to a black base with 4 large rubber feet (measuring 333(W) x 108(H) x 193(D)mm and weighing 3Kg).

CMU-800 main board and PSU.

The base plate rear holds the PSU board, transformer, 80mA mains fuse holder, power switch and direct coupled mains cable, giving +5V, ±15V.

CMU-800 panel board.

Two large boards occupy the underside of the front panel of the instrument, with the top being the 'main board' containing processor logic, including an 8255 programmable peripheral interface, 2 x 8253 programmable interval timers, 74LS138 and 74LS139 for address decoding, some 20 or so transistors and discrete components, plus 'width' and 'offset' presets. All sound generation is done here for the rhythm unit — the digital melody and chord lines give approximate square waves, whilst the bass is more triangular in shape. No tonal changing can be done, except through an 'external signal' input on a synth or by using a sound processor at the output. Eight CV outs are produced on this board, with Clock In/Out (all through 3.5mm PCB mounted sockets), and the computer ribbon cable (via Interface box) secured onto the board. All ICs, sockets and ribbon are direct soldered, with connectors only used to link upper and lower PCBs.

The second PCB 'panel board' is mounted back to back, with 8 PCB mounted 3.5mm 'trigger' sockets plus 5 chassis mounted standard jack 'signal output' sockets. As with all Amdek products, the construction is first class, a separate metal chassis prior to the front panel providing a very sturdy support. Signal mixing and red LED indication of power on and gating operation is also done here.

Screen Software

Having switched on the CMU-800, the MZ-80K is then powered up and the special 'Soft Package' cassette supplied is loaded direct from monitor since it is in machine code. This takes just over a minute (it's quicker than loading Basic!) and immediately runs the program to give a screen menu as follows:

Incidentally, before we discuss the above, it's worth pointing out that the program itself cannot be listed and is virtually impossible to access, since all the micro keyboard buttons respond as the program requests while others are ignored.

Most of the menu is self-explanatory, but if in doubt you could load the sample 'Lady Madonna' program from the cassette supplied to help familiarise yourself with the commands. Pressing 1' key, you are requested for a File Name which can be overridden by the 'CR' (Carriage Return/Enter) key, and the file loaded. This piece used 2025 steps and lasted about 2 minutes (dependent on Tempo setting), taking 45 secs to load that's indicated by a return to the screen menu. All you have to do to play the piece is press key 'P' for once through or key 'O' for continuous repeat. At any time you can stop the music by pressing 'Q' and the tempo can be changed during the piece.

If you've external instruments playing with the Amdek sounds, a press of the 'T' key gives A=440 (+10 cents). To transpose the whole piece into whatever key you fancy, simply type 'B' and enter the semitone bias from +24 to -24 (away from middle C). Another interesting feature is the ability to change the CV bias. Typing 'C' and entering from +24 to -24 will change the external synth pitch, but will keep the Amdek channel as normal, so you can put external sounds at other pitches for further harmonic effect. Saving on cassette is as easy as loading, and a Verify operation makes sure all is well. During all screen calls, the display changes and tells you what is happening, prompting you at various points for more information.

Composing with the Editor

The Editor 0-9 indication on the menu provides the screen pages to compose your music. If you're starting from scratch, you'll have to load the master program again, otherwise your last program's still in memory with no way to clear it in one operation. The Editor code numbers refer to the Channel numbers as explained earlier. Since those are printed left to right across the Amdek front panel, it is easy to remember which channel to select.

Channel 0 Rhythm programming.

Selecting the 0 key, you are asked for a Pattern Number. By the way, if you fail to give a number, the software provides a 'default' number itself (usually whatever was last chosen, to be sensible). The display then changes to show a 'dot' grid 16x7 steps long that lets you place an X where you want one of the seven percussion sounds to play. These are Bass drum, Snare drum, Low tom, High tom, Y=long cymbal, Open hi-hat, and Closed hi-hat. A flashing cursor can be manipulated in various ways over the grid, and the Step time can be inserted. The total step time is automatically calculated and a default step of 6 is given initially for 16 steps, totalling up to 96. Of course, any length of measure (bar) can be made simply by inserting 0 step times after the last step required.

In this Screen Editor Mode, all the keys move the cursor in a downwards loop over the grid, jumping back to the top for repeat, while the cursor direction keys jump over inserted X's and dots. Typing 'C' gives a copy function of any previous pattern entered, and 'M' gives instant play of the rhythms as it stands. If you ask for a new pattern number to work with, you always get the next one available, with a maximum of 240 possible rhythm patterns to make (each one uses up 17 steps!) provided you've enough memory left. Switching back to menu (typing 'Q') you can then enter channel 0 and specify the order you want your rhythm patterns played. You can do a sound check to confirm the order and at any time you can put the other parts with it by getting back to the screen menu with 'Q' and then using 'P' or 'O' to play.

Entering the melody line on Channel 1.

Entering the notes is done with channels 1-8 and since it's really the same for each of these, we'll look at Channel 1. As with Channel 0, if you are entering information in a completely new measure, the screen automatically goes into 'Insert Mode', instead of Screen Edit mode. Information is entered by any number of steps in each measure with you inserting CV, Step and Gate time for each step. The semitone pitch of each note is set by a number from 0 (for C two octaves below middle C) to 102. It's unlikely that your external synth will go up to this range (normally the 'footage' takes care of pitch range). Default figures make it hard to make mistakes, provided you keep the total step time of each bar the same length for consequent channels you prepare — that is, unless you want melody in 3/4, bass in 4/4 and so on!

The cursor controls are most useful and jump from CV to Step to Gate line by line. At the same time a set of Screen Edit control keys is available for:

* : Measure End
[ : Repeat Top
] : Repeat End
. : Copy Last Step
I : Insert
F : Next Screen
B : Last Screen
C : Copy
T : Transpose
D : Delete
= : Sound Edit
M : Measure Play
P : Point Play
Q : Quit

Taking these in order, the comprehensive screen editing allows a Sound Edit (=) at each step, at each point a full play of all parts can be done (P) or a single bar with the channel displayed only played (M). The Insert command enables you to drop into any step of a measure and alter the pitch, step or gate. Measures can be copies from one channel to another any number of times with a semitone bias (transpose) up or down. This will also put existing measures one measure on. Individual steps can have the same treatment with the Transpose function. Any number of steps from the first in a measure can be deleted, or specific steps can be altered. A full stop (dot) simply copies the previous step wherever you've located the cursor. The repeat signs are inserted as immediate 'before' and 'after' repeat markers — this was the only command that didn't appear to be executing correctly — it kept on repeating! It also stops 'looping' taking place in the other parts. The measure end is made by typing the 'asterisk' key instead of a CV number and you 'quit' your entry with 'Q' to jump to the menu again.

So that's it — a remarkable little package that offers a lot of scope for the musician that could well prompt a new interest in the home micro, especially at its low price of around £400. The in-built sounds are fine for use as accompaniment, although the optional CVs to external synthesisers will be something you'll want to use, especially for melodies and solo counterpoints. This facility also puts the instrument into the professional user market. The percussive sounds are pretty good, with a full bass drum 'click', a snare drum that has a slightly high basic pitch, two different pitched toms, and three metallic cymbal sounds which range from 1½ seconds to a short tap. I would have liked preset adjustment for these individual sounds and an accent control. You'll also have to check your earthing with the computer to minimise background noise — then acceptable recording levels can be reached. Although no realtime keyboard to micro record facility is used, this system may well be a viable alternative because of its versatile 'sound editing' through the screen pages — you can hear your composition grow as you play the keys. But in the Compu-Age the keys are on the micro!

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Electronics & Music Maker - Copyright: Music Maker Publications (UK), Future Publishing.


Electronics & Music Maker - Feb 1983


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Gear in this article:

Expansion Board (Computer) > Amdek > CMU-800

Feature by Mike Beecher

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