ZX Computing

Midi Interface

Publisher: Cheetahsoft
Machine: Spectrum 48K

Published in ZX Computing #38

Fast emerging as the home musician's supplier, Cheetah venture into a more sophisticated application

MIDI Interface

Perhaps the most exciting development in the musical field has been the advent of keyboards and synthesizers which use chip-based technology. As this is similar to that used in computers, the possibility of connecting the two has existed for some time now.

In home computing terms, the advent of the MIDI standard - Musical Instrument Digital Interface - has meant that for £100+ you could link your Spectrum to a keyboard equipped with MIDI sockets and perform a variety of control functions such as editing synth sounds or, more generally useful, set up musical sequences.

Up until now a sequencer program would either be "real time" (you play and record like using a tape recorder), or "step time" (where you enter notes one at a time at the keyboard).

Such programs, because of their specialist application and limited market, cost a lot. Usually, between £20 and £50 each and were aimed at recording studios and music enthusiasts. However, such MIDI keyboards have dropped dramatically in price and can now be purchased from around £150+.

Cheetah have now identified a more general market for MIDI users and produced their own interface, complete with sequencing software for £49.95, by far the cheapest available.

The Interface

This is the usual dead ended plastic case which plugs into the user port of the Spectrum. At the rear are three 5-pin DIN MIDI standard sockets providing IN, OUT and THROUGH connections. These are bolted on behind the plastic case and I found that some of my DIN plugs did not have enough reach to plug in. The holes in the plastic casing are not wide enough to allow the plastic covering of the DIN plug to pass. The result is connections which are not very secure. Provided the set up is stable, then there is no problem, but if the computer moves then a lead may fall out. This even applies to the supplied DIN lead.

The through socket also doubles as a synchronisation socket for sequencers sending 96, 48 or 24 pulses per quarter note via pins 1 and 3.

Considering the price, the unit is very good, although the socket holes should be enlarged.

Reading the specifications for the software aroused my curiosity. Presented in a minute, eye-straining 18 page "instruction manual", the program seemed to offer a rather sophisticated range of operations.

"The system will allow you to record up to eight tracks of music, each track having sixteen verses stored in it, each verse being from 1 to 64 bars in length. Each track may be assigned to any one of sixteen music channels and a song constructed and played on any or all of the eight tracks simultaneously."

Not only that, but the music can be entered in real time or step time and edited in step time regardless of which method of entering the music was used.

Each verse can contain a single note sequence or a polyphonic sequence, a very powerful choice, and there are ten degrees of quantisation or auto-time correction, ranging from none to half-note accuracy.


On loading the program after connecting up the interface, the screen offers a microdrive copy to be made. Declining this option presents you with a full 22 lines of options including: Record a verse, Track and verse to record, Adjust a verse length, Link two, or copy one verse, Delete a verse, Reverse a verse, any many more.

Selection of an option is by moving a bar up and down the screen and pressing Enter. This often leads to a sub-menu where parameters or further options can be selected, also using the cursor keys.

In Use

I spent a while with it, using the Cheetah MK5 keyboard as an input source and a Casio CZ101 synth as the sound source connected to the MIDI out. The interface itself does not produce any sound.

It is impressive and I enjoyed working with it. Some respectable music was created fairly quickly, and every "I bet it can't do..." thought that occurred to me was proven wrong. I couldn't think of anything that it couldn't do!

There are, however, a couple of minor shortcomings. First, it does not automatically turn off all notes when you stop the sequence play option and all too often the synth continued to play a note indefinitely after leaving that option. The ony recourse was to turn off the synth. If you have several keyboards set up with specific control features, then this could be rather irritating and time-consuming.

Although the playing range is eleven octaves, only the five from 4 to 8 actually operated with my synth, lower and higher notes being played at the highest octave it was capable of. I suspect within a few limits this will apply to many keyboards apart from the full-sized piano simulators.

When in step-time or edit mode, the music is displayed in pianola fashion bar-lines, which vary in length depending on how long the notes are. These are displayed one octave at a time and are positioned vertically. Bars are defined by double vertical lines split by single lines depending on the time signature. Horizontal and vertical editing cursors allow you to select the note you wish to modify.


For home and general use, the interface is brilliant. Well worth the money and it extends the use of any MIDI equipped instrument fantastically. To the enthusiastic amateur, or for semi-pro applications, it is excellent value.

Although the MIDI codes are standardised, unfortunately the MIDI interface ports which make the connection to the computer are not. So far, every interface I've tried uses a different combination for Status, Send and receive; to my disappointment this interface is no exception. You cannot use XRI or EMR MIDI software with the Cheetah interface. A pity, as it would have made the unit more viable.

It is compatible with the ZX Interface 1 and microdrives and, I believe, the Discovery Disk drive.

All Cheetah have to do now is bring out a good, independent sound generator on the lines of the TX7 or FB01 for under £100 and a complete studio set up will be available at a reasonable price!