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Quark LRM2 MIDILink

Long-distance MIDI transmission is no longer a dream, now that Quark have developed a system that converts it into a more durable format. Annabel Scott reports.

It doesn't take long to work out the benefits of MIDI. And about ten minutes longer to work out its limitations. Most of these limitations - such as not being able to feed two inputs from one output, transmit from more than 15 metres, or merge two MIDI clocks - exist as part of the MIDI specifications, and they're all there for very good reasons.

But that doesn't mean it wouldn't be handy to get over some of these limitations once in a while. A London company, Quark, have addressed a couple of MIDI-related problems in the past - their 448 and 999 MIDILink units, for instance, allow you to patch different combinations of inputs and outputs together without removing any leads or changing connections.

Now, with the LRM2, they're having a go at that other little problem - the 15-metre limitation on MIDI transmission. Although the average five-pin DIN MIDI cable is carefully screened, it's recommended only for relatively short-range transmissions because any external interference can corrupt the complex MIDI signal. Transmit over long ranges and you're risking not only interference problems, but also voltage drops from cable impedance. Result? Missed notes, droning sounds, or loss of patch-change or performance information.

Why would anyone want to transmit MIDI over more than 15 metres? Apart from, perhaps, transmission from remote keyboards (for the poseurs among us), that distance would seem to be more than sufficient. But MIDI isn't confined to keyboard use any more. Traditionally, effects units in a stage setting have been controlled by the mixing engineer, but today they're as likely to be MIDI-programmable units under the control of a keyboard setup on stage. Or maybe the mixing engineer has to start or stop sequencers, or the studio engineer wants to patch bulky MIDI units such as a Fairlight through to a controller in another room some distance away.

So long-range MIDI control may be a necessity. How have Quark gone about making it possible? Voltage and cable impedance can't be changed or the system wouldn't function - but perhaps it would be possible to convert the MIDI standard to something a little more durable, then convert it back again?

Well, this is exactly what the LRM2 unit does. The chosen transmission system is RS423A, one of the computer standards which inspired MIDI in the first place. It operates along a balanced line cable, so greater-than-normal lengths can be used without loss of signal quality, and it uses screened twisted pair cable, which can be straightforwardly connected to an ordinary XLR socket.

In practice, it's necessary to buy LRM2 units in pairs, each unit having two independent send or receive sections. On the front panel there are two sets of MIDI In/Thru/Out pockets, and these are duplicated on the rear panel (don't attempt to use both front and rear connections at once). On the rear panel there's a male XLR connector for RS423A Send, plus a female XLR for RS423A Receive.

This means a pair of LRM2 units connected by four cables can cope with two MIDI masters (say, a sequencer and a keyboard controller onstage) and two slaves (say, a pair of expanders, or even two stacks of expanders connected by their MIDI Thru ports). Standard screened twisted-pair cable, as in microphone or tie-line cables, can be used, and Quark can supply make-up cables at £8 plus £1.47 per metre.

Provided the cables have all three pins connected up appropriately, the LRM2 will transmit all MIDI information quite happily for 200 metres or so. Quark's original LRM1 model was used successfully on a recent world tour, and the production version LRM2 should be reliable under the most trying conditions. Available later will be a single-channel 'DI' version, which has yet to find a suitable power supply - it consumes a battery in ten hours or so.

So, the LRM2 is a real problem-solver for sophisticated MIDI users on stage and in the studio. Existing tie-lines within any studio can be used for MIDI transmission with an LRM2 added at either end, and a stage box will carry MIDI signals quite happily whether they're intended to control remote MIDI/programmable effects, or stacks of off-stage synthesisers.

Also on the way from Quark is a Modular Distribution Interface, which allows you to install your own choice of MIDI interfaces, DI boxes and other level-matching devices for studio, broadcast and stage situations. At around £2500 for 12 assorted channels, it's a strictly professional item. But the LRM2, the first commercial unit to give MIDI a long-range shot in the arm, looks much more affordable.

Price £239 including VAT

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


Music Technology - Nov 1986

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