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MIDI Medicine

CMS MIDI Analyst

Martin Russ looks at a solution to all your MIDI analysis problems - not software, but a new rack unit from Computer Music Systems.

Software and computers do not always provide the best solution to our problems. If this sounds like a heretical statement, coming as it does from a committed computer user and software programmer, then all the better. My watchword has always been 'appropriate technology' — so whilst the computer has few rivals as a tool for investigating MIDI on a casual basis, for permanent monitoring I would say that a hardware device really is more suitable. To make a comparison with audio, you could use a cheap pair of headphones for checking that there is a music signal present on some wires, but for serious listening you would need a decent pair of hi-fi speakers.

If you have ever looked at the SOS Software pages then you are probably already familiar with my 'quick and dirty', computer software based approach to looking at MIDI — my 'System Exclusive' and 'Adventures In MIDILand' series have produced a wide range of simple Atari ST programs which allow you to check the Channel and System Messages, as well as monitor MIDI clocks and even test MIDI networks. But using these utility programs will tie up your Atari ST, so it's impossible to use them at the same time as your ST sequencer — even in these computer-literate days, few people own two computers. So until recently, the professional user in search of a hardware MIDI analyser was restricted to some very expensive and functionally limited units from the mainstream Japanese manufacturers — but this has now changed.

The MIDI Analyst comes from Computer Music Systems of London — best known as dealers in a comprehensive range of music software for IBM PC-compatibles - and this MIDI analyser, filter and test set is a useful and welcome addition to their product portfolio. The unit is housed in a convenient 1U 19" rack-mounting box, with MIDI In, Out, and Thru sockets duplicated on the front and rear panels (six sockets in all). The MIDI Ins are not merged, so you can use only one at a time — however, if you use the Analyst in conjunction with a MIDI switching unit, you can arrange to disable the rear panel In and then use the front panel sockets for temporary testing. The two Thrus are exactly what their name implies — hard-wired copies of the In — but the Outs can process the MIDI data with Output Filters (see below). However, because the two Outs normally just echo an unfiltered version of the input (introducing only a minimal delay), it would be possible to leave the MIDI Analyst permanently connected to the output of a sequencer in a small MIDI system, so that it would be instantly on hand when needed. Alternatively, in a larger system, it could be wired to a MIDI switching unit so that you could select it with special test programs for checking and monitoring the entire MIDI network.


The Analyst is designed to be easy to use. For example, it powers up in the Data Analyser mode, so you can look at data immediately. There are only four buttons on the front panel (plus a power switch): two scroll through options, one gets you back to the previous menu, and the last one selects or changes the selected parameter. When you first power up, you are greeted by a start-up message on the 2x16 character backlit LCD display, and the display then changes to the default Analyser option and waits for MIDI data to arrive, whilst displaying the hard-to-misinterpret message: NO DATA PRESENT.

Pressing the Menu button and then scrolling reveals the seven options on the top level menu: Data Analyser; System Real-Time Analyser; Utilities; Data Memory; Output Filters; Display Filters; MIDI Time Code Reader. As you scroll through, you just press the Select button to select that option. If there are further options at the next level down in the menu structure, then you just repeat the process to select these, and use the menu button to step back through the menus. The user interface is simple, quick to learn, and easy to use — and how many reviews of today's complex equipment can say that?

The Data Analyser mode displays MIDI Channel messages (and System Common messages like Song Pointers and Tune Request messages), so if you play your master keyboard it shows Note Ons and Offs, All Notes Off, Note Ons with zero velocity etc.

The channel number, note and octave, MIDI Note number and velocity are all clearly displayed. It very quickly reveals unexpected features of your instruments — for example, I did not know that the Yamaha SY77 sends out a Sustain Off (MIDI Controller Number 64) message when you stop a pattern playing. I do now!


The Display Filters are used in conjunction with the Data Analyser function, to specify exactly what sort of MIDI messages you want to see — those that you aren't interested in will be ignored. You can set the following filters: Note On; Note Off; Any channels you choose (Mute); Display only 1 channel (Solo); Poly Pressure; Channel Pressure; Program Changes; All Controllers; Pitch Bend; System Messages.

You can also use these filters to process the MIDI messages which pass to the Out sockets — the Analyst defaults to all filters off, so normally all messages are passed through without any changes. System Exclusive messages are shown by an indication of their start and end, together with the manufacturer ID byte.

The System Real-Time Analyser displays MIDI Timing Clock messages, Start, Stop and Continue messages, and shows the tempo of the incoming clocks as well, with tenths-of-a-bpm resolution. Active Sensing is shown by a capital 'A' in one corner of the display. There is also a global filter for Active Sensing and MIDI Clock messages, which affects both Display and Output. The MIDI Time Code Reader shows the decoded time code in the standard form — HH:MM:SS:FF (hours, minutes, seconds and frames) — and automatically detects the frame rate.


The normal process of displaying Notes and Controllers happens too fast to allow the extraction of any really useful debugging information, and so the Data Memory section lets you scroll through the last 255 bytes. You can also choose to transmit the data again, as you scroll through it — a sort of slow-motion replay. This facility provides a very good way of finding out exactly what is happening in a MIDI system. As a further aid to problem solving, the data can be displayed in either decimal or hex form, in both the Data Analyser and the Data Memory sections.

The Utilities option allows you to select additional features such as MIDI cable test, or MIDI channel test (which sends out a middle C on a selected channel). The Soft Reset option is exactly the same as turning the power off and on again, and restores all the power-up defaults — it also sends an All Notes Off message and clears the buffer. You can also send an All Notes Off message by pressing the left cursor and the menu buttons at the same time — this is the only time you need to press more than one button at once.

The Configurations option takes you to a further menu which lets you control the fine details of the displays — the hex/decimal display setting is here, for example. You can also turn the error reporting on or off, to specify whether unusual or incomplete MIDI messages will be ignored or indicated on the display.


The Analyst is mains powered, via an IEC socket and a supplied mains cable — the fuse and voltage selector (240 or 110 volts) are inside the black folded steel case. There is one PCB, with a Rockwell 6502 microprocessor running at 4MHz, a Hyundai 6116 RAM chip, and AMI 6850 serial interface chip, as well as a few miscellaneous LS TTL chips. The linear power supply is on the same PCB, with an encapsulated transformer. The MIDI sockets are of the conventional PCB-mounting type, although they are not protected against over-enthusiastic MIDI cable insertion, and they are not filtered with ferrite chokes.

The MIDI opto-isolator is a high specification 6N138, so there should be no problems with marginal MIDI interfacing. The LCD backlighting power supply invertor is not encapsulated (unusual), and the associated 'whistling' was at a low level. Unfortunately the LCD contrast adjustment control on the review model was not aligned with the access hole in the front panel, which made altering the viewing angle impossible. The PCB is double-sided with plated through holes and solder resist, and the standard of construction is good. The 46 page A5 manual describes the operation of the unit thoroughly, although more diagrams might have made some of the points easier to follow.


The MIDI Analyst has a wide range of potential uses. It can be used to monitor and check the output of a synthesizer or other piece of MIDI equipment, and so would be a useful servicing and repair tool. In a studio, the monitoring and analysis features should help to iron out any incompatibility problems between different pieces of equipment. The MIDI consultant or trouble-shooter would find it a valuable weapon when trying to track down MIDI problems.


The MIDI Analyst is one of those insidious boxes which you install in your system just to see what is happening, and which you then find yourself using quite a lot. In fact, the convenience of having instant MIDI analysis is very addictive — I can see why the BBC Radiophonic Workshop were among the first customers for the MIDI Analyst. It is all very well having software tools for checking and displaying MIDI, but what happens when you are trying to investigate a computer-based sequencer? Hardware solutions like the MIDI Analyst are a way of providing the same sort of functionality without the need for two computers. If you are at all serious about your use of MIDI, then the MIDI Analyst could be an essential purchase.


£295 Inc VAT.

Computer Music Systems, (Contact Details).

Previous Article in this issue

Shape Of Things To Come

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Going Live

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 - Jan 1991

Review by Martin Russ

Previous article in this issue:

> Shape Of Things To Come

Next article in this issue:

> Going Live

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