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Miditest 5

When is a MIDI lead not a MIDI lead? Vic Lennard looks at MIDI leads, the problems they can cause and an inexpensive way of solving them - the MIDITest 5.

RECENTLY, I WAS called to a studio to help sort out a problem. The MIDI equipment had been going haywire for ten hours, the in-house engineer was baffled. The problem was one faulty MIDI lead.

We take MIDI cables for granted - after all, what can be complicated about a length of cable and a couple of 5-pin DIN plugs? Consequently we tend to buy whatever the local music store has in stock. Is there any reason for spending £12 on a professional three-metre MIDI lead when you can pick up a hi-fi lead for £2?

The actual pin configuration of a MIDI plug, viewed from the plug end, is as follows: pins 1 and 3 are not connected, pin 2 is used for the screen, pin 4 carries 5v DC and pin 5 the MIDI signal.

The MIDI specification states that MIDI cables "shall have a maximum length of 50 feet" and that "the cable shall be a shielded twisted pair, with the screen connected to pin 2 at both ends". Precise enough - time for a little explanation.

Cables exceeding 50 feet are likely to be too capacitive and could cause serious degradation of the MIDI signal. This will lead to MIDI information being lost. Symptoms could be hung notes, due to the loss of a MIDI note off, or even loss of note triggering. The twisted pair is intended to protect the signal lead from external electrical fields. The screen serves a similar purpose, but it's better to be safe than sorry.

So what do you get for your £12? Probably Klotz, or some other high-grade, microphone cable - which is, indeed, a twisted pair - and something like Neutrik plugs with pins 1 and 3 removed. The cheap alternative is likely to be a 5-pin DIN cable with moulded plugs at each end and five-core cable, each core being individually screened.

A couple of years ago a company, who shall remain nameless, decided to use two-core screened cable and solder one lead across pins 1 and 4 and the other across pins 3 and 5 (I suppose it is easier to slop a lump of solder between two pins rather than aim it carefully at one). They then had the audacity to print MIDI on the side of the cable. This shouldn't really have caused any problems but Atari had used pins 1 and 3 on the ST MIDI Out socket, as a MIDI Thru (to save on a third socket). The result when using one of these leads with an ST was chaos.

There are various ways to check MIDI leads. The first is to look at the connections by taking the cover off the DIN plugs. Unfortunately, many manufacturers now use moulded plugs... Secondly, you could use a resistance meter to see whether pins are soldered together. The problem here is that it's rather awkward to hold the probes to the pins without shorting against the metal casing of the plug. The third option is the MIDITest 5.

MIDITest are a new, East London-based company, and the MIDITest 5 is their first venture into music technology. The unit allows you to check the precise connections within a MIDI lead. The MIDITest 5 consists of a small black plastic case with two MIDI sockets at one end and two sets of LEDs (one green, the other red) each in a semi-circular arrangement. These resemble the pin layout of a MIDI plug - with one extra yellow LED in the centre of the arrangement. A rotary switch with its six positions labelled, corresponding to the MIDI plug pins, completes the arrangement. Power comes from a PP3 battery, accessible from the back of the box.

The only instructions necessary for use are to plug in a MIDI lead and start turning the switch. The LEDs from each pin layout light up showing which pin is connected to which other. The central yellow LED checks for any connection between a pin and the casing of the plug. Bona fide MIDI leads will only have the pairs of LEDs for pins 2, 4 and 5 lighting up. Five-pin DIN cables that are suitable for MIDI applications will light up all five pairs of LED's.

The tester immediately picks up on the four most common faults: the mirror-image lead used by some audio equipment where the LEDs in one set will rotate in the opposite direction from the switch; the incorrectly-soldered leads mentioned above (selecting pin 1 will have pins 1 and 4 lighting up on one of the sets of LEDs); a broken connection will only light up one of a pair of LED's; and a pin touching the casing lights the yellow LED (this will cause problems because most MIDI equipment has the socket casing earthed). It's difficult to see how the operation could be made simpler or easier to perform.

And at an RRP of £14.50, this little device is a necessity for anyone with a burgeoning collection of MIDI leads - it'll put you one up in the battle against the lost or hanging MIDI note.

Price £14.50 (mail order) plus £1 p&p.

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Hybrid Arts SMPTETrack II V5.09

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


Music Technology - Aug 1990

Gear in this article:

Connectivity > MIDITest > MIDITest 5

Review by Vic Lennard

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