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Vesta Kozo MDI-1

MIDI to CV Interface

MIDI to CV conversion made simple.

Vesta present a cost-effective way of giving your old CV synth a new lease of life as part of an up to date MIDI system.

Vesta Fire have launched a range of products, with the name Vesta Kozo, to extend the choice far beyond the familiar footpedal effects. The new range is aimed at the rack mounting market and includes some original ideas, like their CV controlled DIG-420 Sampler, and the more conventional DIG-412 which is a MIDI-equipped, programmable digital delay unit. The item which fell into my hands was a MIDI/CV converter, the MDI-1.

This particular unit is presented as a suitable companion for the DIG-420 sampling device, as the two units together give the option of controlling samples from either MIDI or CV, but the MDI-1 also has a place in the market in it's own right.

I deliberately didn't use the DIG-420 sampler to check out the MDI-1, as I was chiefly concerned with how it would perform as a means of persuading my much loved (but recently neglected) CV and Gate controlled, monophonic synthesisers to co-operate with a MIDI system. From my own point of view a unit like this is highly welcome. I have bent more than one ear about how many excellent synths have been tucked away in bottom drawers awaiting just such a new lease of life.


My first surprise was just how solid this little unit felt. It's a chunky 7" x 6" x 2" in size, and solidly built.

The manual is worth a quick mention if only for one classical, inescapable, and inscrutable piece of logic. Vesta Fire (and Kozo) are not alone in finding it difficult to provide translations for technical equipment manuals, and I wonder how well British manufacturers do with the Japanese versions of their literature. Anyway... after struggling through a list of 'Names and Functions of each Part' I was relieved to read the following: 'No. 10. Power Switch. This is the power switch.' What more can you say?

Connecting Up

Most of the practical testing of the MDI-1 was done with a Casio CZ101 or a Joreth MCS driving a Moog Rogue. It didn't take long to get things operating successfully and once you are familiar with what has to be done for your particular CV synth, it takes very little time to set up. I was disappointed that the interface only operates one way, MIDI to CV; there is no CV In on the unit to allow pitch control over a MIDI keyboard from a CV master. I'm in no doubt that this would greatly increase it's appeal but I can only assume that Vesta were concerned with cost. I should point out that there is a Trigger In on the box, but in the context of what I was doing, the ability to operate a voice on a MIDI drum machine from a Moog Rogue wouldn't go high on my list of priorities.

"I was disappointed that the interface only operates one way, MIDI to CV; there is no CV In on the unit to allow pitch control over a MIDI keyboard from a CV master."

If you have the DIG-420 at your disposal then the Trigger In starts to look a lot more useful, as it can be used to synchronise a sample recording. Another feature that might be worth including on future versions is the ability to transmit pitch wheel information. Again, my guess is that the manufacturers wanted to keep the price of their unit as competitive as possible, but the use of pitch wheels is so much a part of synth playing it seems a surprising economy.

By way of sockets, the MDI-1 has a switchable MIDI In/Out and a MIDI Thru, a Trigger In, a Trigger Out and a CV Out. All the sockets are found unsurprisingly on the rear, and the other controls are sparsely and simply laid out on the sloping front panel. There is a single knob for fine tuning between MIDI source and CV slave, and a hole marked V/Oct to allow you to insert a screwdriver to calibrate the unit for various makes of CV Synth. May I draw you attention to the fact that the manual sensibly advises great care when adjusting this control!

The Rogue that I was working with employs a one volt per octave system and it was unnecessary for me to use this facility. Certain Korg and Yamaha synths operate on a one volt per Hertz system and will not work with this system.

The remaining control is a Select button which toggles through five Modes, each clearly labelled and accompanied by an LED to let you know where you are. The front panel also boasts a neat circuit diagram to help you understand (hopefully) the manifold potential of the box itself. There is not much that can be said about the quality of operation as such a box as it either works or it doesn't, and this one does.


I found the unit a very simple device to use, particularly when I realised that Mode 3 (MIDI Record) and Mode 4 (Trigger In Record) mainly relate to the DIG-420. For my own purposes the simple routine of starting with MIDI Initialise, moving to Trigger Out Polarity to switch positive to negative (for my Rogue) and then on to MIDI Play, got things sorted out very reliably. After that, all that remained to be done was fine tuning using the Tune knob on the MIDI Box or by tuning the Rogue itself.

It did not go quite that smoothly first time of course. I confess that although there is nothing strictly missing from the relevant section in the manual, I did not immediately realise all the implications of MIDI Initialise. When you have connected your keyboards and interface and switched everything on, the first thing that is required of you in the MIDI Initialise mode is to play a note on your MIDI keyboard. A number of things happen at this point. First the MIDI Box automatically selects the MIDI Channel of your MIDI keyboard and switches from Omni On to Omni Off. Also the relationship between the pitch of the MIDI master keyboard and the slave CV keyboard is set up. This last fact caused me a bit of head scratching at first, but when I got the hang of it, it was also what made the MDI-1 seem most useful. The MDI-1, like it's stablemate the DIG-420 is designed to operate over a maximum of three octaves, which is plenty for a monophonic sampler and adequate for a lot of older monosynths. MIDI keyboards however, tend to have at least 4 octaves. This is all important as the first note in MIDI Initialise sets the upper limit on your MIDI Keyboard for sending signals out via the CV interlace.

"The MDI-1, like its stablemate the DIG-420 is designed to operate over a maximum of three octaves, which is plenty for a monophonic sampler and adequate for a lot of older monosynths."

One of my main aims was to use the Rogue to reinforce a monophonic line while playing the MIDI synth. The Initialise function allows you to decide (within reasonable limits) which part of your MIDI keyboard gets doubled by the CV slave. Most effective to my way of thinking, was confining the doubling to the lower end of the MIDI keyboard. In practice this meant I was getting a layered sound for a single note bass part in the left hand, and the MIDI keyboard only for chords in the right hand. One thing to be aware of is that if you are using the unit to drive a CV keyboard in this way, don't forget that the synth will only cope with one note at a time. If you play chords on the master keyboard within the range set to control the slave, it remains to be seen which note will actually get played by the slave!

It won't be a random effect though, it will select the note played by the latest finger to go down. If a chord gets played on the MIDI keyboard, the response from the CV synth may therefore be unexpected and undesirable. This is an inherent problem of trying to drive a monosynth, from a polyphonic master, and is in no way a limitation specific to the MDI-1. If you are dealing with purely monophonic sources, live or from a sequencer, the problem should never arise.


The merits of the Vesta Kozo MIDI/CV interface are not difficult to appreciate. It's an uncomplicated but surprisingly versatile little gizmo. The value of a device which lets you control a CV keyboard from a MIDI synth, sequencer or composer will be apparent. The price of the MDI-1 is well below that of a MIDI-controlled synth, or expander. You will understand that it would be unfair of me to do anything but generalise about it's use with the DIG-420, but the concept of a CV controlled sampler working in tandem with the subject of the review must be of interest to many people purely because of the range of options it provides. I gleaned one little example from Vesta's UK distributors, MTR. You can get up to 8 seconds of sampling from the DIG-420, at an admittedly modest bandwidth, and selection of the length of sample recording can be made via the MDI-1 from a MIDI keyboard! How many other little tricks this dynamic duo have up their sleeves I wouldn't like to guess.

From the point of view of someone who regularly works with a computer-based composing system, it makes sense to have a rack mounted sampler, and if you can also start incorporating the old favourites like the pre-MIDI Moogs, ARPs and Korgs, then it certainly gets my vote.

The MDI-1 is unlikely to win prizes for original design concepts, and their manual is very unlikely to get on the short list for next year's Booker Prize. I would personally have liked to see the interface doing CV to MIDI as well as the other way round and I wonder just how much more expensive such a unit would have been. All in all I think Vesta have a product which could be very useful to a lot of people in all sorts of situations. I am well aware that there are those who would prefer to forget the days when Moog ruled OK, but in my view, any piece of equipment that might re-establish a more active role for the CV generation of synths in a world so heavily dominated by MIDI has to be recommended for serious consideration. If Vesta have achieved this goal at a price which makes economic sense, and it seems to, then the MDI-1 is more significant than its appearance might suggest.

The Vesta Kozo MDI-1 retails at £132 including VAT, and further information is available from: MTR, (Contact Details).

Also featuring gear in this article

Previous Article in this issue

Yamaha MT1X

Next article in this issue

Putting the Record Straight

Home & Studio Recording - Copyright: Music Maker Publications (UK), Future Publishing.


Home & Studio Recording - Jun 1986

Donated & scanned by: Mike Gorman

Gear in this article:

MIDI->CV Convertor > Vesta Kozo > MDI-1

Review by Mick Jones

Previous article in this issue:

> Yamaha MT1X

Next article in this issue:

> Putting the Record Straight

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