Practically MIDI (Part 8)
Martin Russ pretends he’s Dick Barton, Private Eye, for the very last time and brings his series to a close with a Guide to MIDI Troubleshooting.
I get lots of enquiries from people suffering from problems with their MIDI networks. When faced with such a problem I follow a set sequence of actions which often results in a timely cure. Since this series aims to help all you aspiring MIDI users out there, I thought it was high time that I gave some formal tuition in MIDI DIY! Next time something goes wrong with your set-up, don't go unplugging MIDI cables at random, instead, try following this list of procedures.
Draw a large, clear diagram. Write your name and today's date in the bottom right-hand corner and keep it safe. This diagram should show how you think your MIDI network is connected together. Draw a rectangle for each MIDI instrument and clearly mark the Ins, Outs and Thrus.
Figure 1 shows the sort of diagram I mean.
Now look at the reality. Check that MIDI Outs and Thrus are connected only to MIDI Ins. There should be no In to In connections, nor Out to Thru or Out to Out connections. It is very easy to do this sort of thing incorrectly when you are assembling even quite small MIDI networks, especially when you are in a hurry. Figure 2 summarises the correct and incorrect connections. Use the diagram you have drawn to confirm that what you expect to see is what you actually find.
Make sure that you are aware of any software switchable Thru or Out connections in a particular piece of equipment. As we saw last month, some sequencers and tape sync units, as well as other devices, can offer built-in features which allow them to merge their own data with that received at the MIDI In port and then send the resultant data to the Out. If you know what is happening then all is OK. I use reminder labels on these 'Outs with Thrus' so that I can check that the device is doing what I want, not what it wants to do. If you are not fully aware of what is happening then it is very easy for a data loop to occur, and then anything can happen (and will!).
Get a track sheet from a 16-track studio and use it to make a note of how you are allocating the 16 MIDI channels to particular instruments. Make a careful note of any instruments in your network which only work in Omni mode, or on a restricted number of MIDI channels. Date and keep this sheet with the above mentioned diagram.
Look at your network diagram. Is there any master timing source? What are you syncing to or from? Which device is providing the timing clocks for everything else?
You should have either no master timing source or just one. If you have two or more then you have a recipe for disaster. If you are just using the MIDI connections to parallel up lots of MIDI keyboards, then you will not normally be using a timing source, or the timing source will be non-MIDI - something like a separate drum machine (or even a real drummer!).
For more complex set-ups, where you might have a sequencer and drum machine connected, you need to be sure who is in control. Hopefully you are, but it is possible to have a sequencer and drum machine running at similar but different tempos, with the result that it is impossible to play in time with both!
You should have no long chains in your MIDI network anyway, but in case any have slipped through, now is the time to eradicate them. Buy a Thru box and 'star' your network (see SOS Sep 86). The master keyboard should connect directly to a Thru box and each expander, sampler, peripheral instrument should be connected to the Thru box. Figure 3 shows the sort of arrangement to aim for. You can buy Thru boxes very cheaply, like the Philip Rees V10 with 10 MIDI outputs, so you should not run out of available outputs quickly. If you are working in a studio, then they should have plenty of Thru boxes of their own or they will have a MIDI network already wired up for you to plug into.
Check any battery-powered equipment. If at all possible, it is as well to try and avoid using any batteries at all. Mains adaptors can save a lot of effort trying to troubleshoot a system whose only fault is a Thru box which has run out of 'Thru'! Some instruments like remote, over-the-shoulder, performance keyboards are only practical with batteries in some circumstances, so do what most sensible roadies do and always fit a new set of batteries before each performance. Rechargeable batteries can be a help in minimising the cost of this sort of strategy, but they have the disadvantage that they need a lot of time to charge up (usually about 14 hours - so overnight is the best way). The Yamaha KX5, for example, is notorious for producing spurious MIDI data as its batteries fail, so don't trust the fact that the LEDs on your keyboard still come on as a guarantee that all is well.
Having checked everything so far, now is the time to make sure that what you have on your diagram is what you have in reality. If you looked at the diagram before and then followed the cables, then do the reverse this time: look at the cables, follow them, and then check what you find against the diagram. It is very easy to presume that a cable is connected to a particular socket, simply because the diagram shows it and it is going in the right direction.
Check that cable! Be especially vigilant with cables which are wrapped around each other, or which disappear into a knot or tangle and emerge on the other side. Check that the cable you are following actually is the one which looks as if it appears on the other side. Most MIDI leads have black plastic moulded plugs and cable - each looks just like all the others. Try shopping around for some different coloured cables or DIN plugs, or use the self-adhesive coloured paper shapes available from stationers to mark your cables, so that you can find the opposite end of a long lead even when it is in a tangle. Heat shrink sleeving can make a more permanent job of this, as the stick-on labels have a habit of falling off at the wrong time. Similarly, the key tags that people fasten to keys to identify them can also be used to help you locate a lead a long distance from its source - write a meaningful label like 'DX7 Out' or 'Midiverb In' or 'ST In', etc.
If you use such leads for switching between MIDI data sources, so that you can perform dumps to a MIDI Data Recorder or computer, then consider buying a MIDI Switcher or Selector. The Roland MPU-104 or Philip Rees 5X5 selector units are ideal for this purpose, and can be recommended. The less you need to alter your MIDI network, the less trouble it will cause.
If you encounter a problem when using your MIDI network, then refer back to your diagram (you did draw one, didn't you?). Try to split it into small functional blocks and thereby attempt to isolate the problem. Merge boxes can be a potential source of problems, so investigate their behaviour carefully. Some Merge boxes overload gracefully, whilst others throw tantrums. Do not be afraid of pulling all the MIDI cables out and starting again from scratch. There is nothing worse for your time and temper than to try and reconfigure the cables without knowing what you are really doing. If in doubt, don't waste time trying to figure out what you have done wrong. Starting again and keeping a clear idea of what you are doing will eventually sort things out. Keep in control of your network and it will help you; lose control and you lose everything.
This is the time to get out your MIDI Monitor! (See SOS Feb 88 for construction details.) Use it to check that the MIDI data is getting to where you expect. Plug it into the Thru socket on the piece of equipment in question and play some notes on the master keyboard. The LED should light if all's well.
A lead tester should be part of everyone's tool kit. MIDI cables are particularly difficult to test with a multimeter, so investing in a dedicated lead-testing device could be very useful. An example of the sort of thing to look for is the aptly named 'Wotabox', which will test a range of connectors and cables including XLR, jack, phono and MIDI, as well as testing fuses.
That is all from Practically MIDI for this series. When I have gathered together some more gems of wisdom from my experiences I will get back to you. Consider this to be the end of the first byte (there have been eight bits so far!). I hope you have enjoyed this diverse journey through the mysteries of the 5-pin DIN plug. Don't be afraid to drop me a line via Sound On Sound if you have a problem - who knows, it may feature in the next byte! Those who know me have already recognised their own problems regurgitated in these hallowed pages - you could join them!
Finally, I would like to thank everyone who has contributed, however indirectly, to this series. As this includes most of the manufacturers and suppliers in the music business, there are too many to thank individually. Ta!
Addresses of items mentioned:
- V10 Thru Box; 5X5 Switch Box:
Philip Rees (Modern Music Technology), (Contact Details).
- MPU-104 MIDI Selector:
Roland (UK) Ltd, (Contact Details).
- Wotabox Lead Tester:
Kingswood Studios Ltd, (Contact Details).
Feature by Martin Russ
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