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XRI Systems XR400 MIDI Mate

Is your MIDI system just an accident waiting to happen? Here's an easy way of bringing order to your present tangled mess of MIDI connections. Martin Russ checks out XRI Systems' clever XR400 MIDI Mate.



If there is one thing sadly lacking in most MIDI systems, it is organisation. Most MIDI users seem happy to repatch their system whenever they need to do something different, like adding a new expander or multi-effects unit. But as the size and complexity of MIDI systems increases, you find that the task of rewiring becomes more difficult to comprehend, and if more than about five devices are involved it can become unmanageable!

Recent times have seen the release of many devices designed to ease the integration of MIDI into a musical working environment. These are usually MIDI patchbays - but if the user is always repatching MIDI cables, then a MIDI patchbay is a solution that only solves the symptoms, not the cause. To find the cause, you need to ask why you need to change cables...

One reason is that you might want to use a different master controller keyboard, or even a wind or guitar controller, as the source of notes. Perhaps you want to use a computer-based editing program and so need to connect the computer and device together. Or you might want to use a drum machine as the source of synchronisation clocks, instead of a sequencer.

The ideal solution would be to connect your MIDI system together and be able to do whatever you wanted without changing any cables. A close study of how MIDI systems work and some innovative thinking has produced something which does just that. No, it is not another patchbay - it is what I will call an 'auto-router': the XR400 from British manufacturer XRI Systems.

AUTO-ROUTING



What does a MIDI auto-router do, and why is it different from a MIDI patchbay?

Well, the first difference is that there is no need for separate configurations or memories, and there are no MIDI control facilities. Unlike a patchbay, where you need to decide on the connections and programme them in, the XR400 auto-router 'intelligently' does the switching for you, without any need for programming. Whereas most MIDI patchbays have lots of front panel switches and displays, the XR400 has three simple switches and five LEDs - definitely an 'easy-to-use' user interface. The most important difference is that the auto-router does all the hard work for you - you just plug in your MIDI equipment and go, whereas most MIDI patchbays demand a certain amount of forward-planning and programming, and perhaps even software to make it effective.

This all sounds too good to be true, so how does it work? The XR400 consists of a three-way merger with a six-way selector switch on one input and an 11-way Thru, with special connections for the main master keyboard and the sequencer. But the really clever stuff is in the programming of the microprocessor inside. It monitors what is happening on the MIDI system at any given moment and configures the connections accordingly - so it automatically prevents MIDI loops by stopping the output from the master keyboard from ever reaching its own input. When you send System Exclusive clumps from a computer or data filer, it uses buffering to ensure successful editing and bulk transfers. Clock start detection (and loop elimination) allows any connected device to be the source of synchronisation signals, which means that you do not have to worry about where the sync source is either!

It is this aspect of the XR400 that really sets it aside from patchbays. Once you have connected it into your MIDI system, then you can virtually forget that it is there; its operation is transparent in almost all cases. By adding a SMPTE/MTC synchroniser (such as XRI's very own XR300), you can make the XR400 the centre of a complex tape sync setup as well. If you need more MIDI inputs and outputs then XRI will soon be announcing a 16x16 patchbay, equipped with the same 'intelligent' merging as found in the XR400, with a built-in XR300 SMPTE/MTC sync box as well. For patchbay fans there is a separate 8x8 patchbay also about to be released.

HARD FACTS



The hardware is as simple as the concept. The XR400 is housed in a 1U high, 19" rack-mounting steel box. This has a matt black paint finish and white silk screened lettering, along with areas designed to act like a 'scribble strip' for keeping note of what is connected to where. The front panel has five LEDs, which flash when any of the inputs (A, B, C, D, E) are passing MIDI messages, and show which of the six switchable inputs is active by remaining illuminated in either green or red: inputs A, B and C are the six inputs and are referred to as Green A, B and C, and Red A, B and C.

The first of the three pushswitches places the XR400 into a mode whereby it can be used with sequencers which use a 'soft' MIDI Thru, whilst the second switch acts as a Reset button for the whole unit. This actually serves a rather useful purpose: it clears the MIDI buffers when you change between the modes selected by the first switch, and so is useful whenever you want to flush out any MIDI data in the system.

The third and final switch is used to select the input to the six-way selector switch, which connects to the three-way merger. Pressing this switch cycles around the three inputs: A, B and C; the three 'Greens' first then the 'Reds'. (It is good to see that XRI's first choice is Green in these environmentally-conscious days!) Unfortunately, this switch is purely mechanical - you cannot select these inputs via MIDI. But when you think about the idea behind an auto-router like this, then you realise that having removed the need for a programmable patchbay to do everyday things like using the master keyboard and a sequencer, it seems strange to add a patchbay type function just so that you can automate editing of voices.


One of the 'C' inputs appears on the front panel as well as on the rear and is intended to be used whenever you want to temporarily connect the MIDI Out of a device into the unit - a wind or guitar controller might be one example, or perhaps a quick edit to something that is not normally edited and so has no connection permanently wired into the XR400. The corresponding MIDI Out for input C is output 3, and this is also on the front panel, where it can be used when you want access to a MIDI Out but do not want to mess about behind a 19" rack.

The rear panel houses the remaining seven input sockets, with input D dedicated to the master keyboard and input E to the sequencer. Ten MIDI Outs complete the sockets on the rear panel - again, with two assigned for use with the master keyboard and a sequencer. The fused IEC mains socket operates at 240/220V only, with no switching for other voltages. The steel case itself seemed adequate, but the top panel was rather too easy to bend inwards. This is no problem for those users who mount it in a rack and leave it, of course, but there are many people who misuse any flat surface!

One of the wonderful things about companies like XRI Systems is that they respond constructively (positively and literally!) to comments. For instance, after I spoke to Chris Smith at XRI he told me that the top panels of the production models were more robust, but that XRI would, of course, respond to any feedback from users. This has already happened - the early production model XR400 which I had for review only featured three extra inputs; the current model now has six!

INTERNAL INSPECTION



As usual, I opened up the review unit to get some idea of the quality of construction and the technology employed. Inside there was one PCB. The main processor was an NEC 80C40 micro-controller chip running at 12MHz from a crystal, with all the MIDI input and output handled by three 6850 ACIAs into 74HCT series TTL driver gates. The 2764 EPROM was Version 1.2 and, like all the ICs, was socketed for easy replacement. Most of the remaining miscellaneous logic chips were 74HCT series TTL. The power supply was a linear design.

The standard of construction was good, although the PCB-mounted MIDI sockets had no insertion protection and were not RF filtered. (I recommend the Casio VZ8M synth expander to hardware designers as an excellent example of how to protect MIDI sockets from over-enthusiastic users without excessive expense - and at the current price, the VZ8M is a bargain!)

DOCUMENTATION



XRI have packed a lot into the 18 pages of the A4 manual: it shows lots of example MIDI systems, with detailed explanations of how to use the XR400 effectively. There were also a couple of minor spelling mistakes designed to catch out unwary reviewers, eg. 'here' instead of 'hear' and 'principals' instead of 'principles'. Since XRI also design MIDI systems, any technical problems you might have with installing an XR400 (unlikely, I would have said) should be easily solved with a phone call or letter.

CONCLUSION



The choice between a 'no controls' autorouter like the XR400 and a software plus patchbay solution like that offered by Dr.T's X-Or really depends on what you want your system to do. If you want ease of configuration and occasional editing, then selecting with a few presses of the XR400's input select button should not bother you. For those who want integrated software with lots of editing and System Exclusive snapshots of complete system setups, then the patchbay route is what you need.

I have been looking at MIDI patchbays for some time trying to find a suitable replacement for the custom-designed MIDI switcher unit which I built some time ago, and so far the XR400 comes closest to what I want (it is good to be able to praise an innovative UK-designed and built unit). As with almost any decision you will need to weigh up your needs before you choose, but for many hi-tech musicians the XR400 could be exactly what their MIDI system has been waiting for!

FURTHER INFORMATION

£219.95 inc VAT.

XRI Systems, (Contact Details).


Also featuring gear in this article



Previous Article in this issue

Recording Techniques

Next article in this issue

DAR Soundstation II


Sound On Sound - Copyright: SOS Publications Ltd.
The contents of this magazine are re-published here with the kind permission of SOS Publications Ltd.

 

Sound On Sound - Apr 1990

Donated by: Bert Jansch / Adam Jansch

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MIDI Patchbay > XRI Systems > XR400

Review by Martin Russ

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