A product of Roland Digital Group - the American division of the Japanese parent company, the MPU is a MIDI-to-computer interface that supports MRC, an eight-track polyphonic recorder program, initially for the IBM PC and Apple only.

Standard UART MIDI interfaces leave all data handling and protocol to the programmer, and the MPU401 contains its own processor and gate arrays that make realtime composer programs a good deal easier to write. The serial format and simple UART interface specifications for MIDI help to keep hardware costs low for the prospective computer musician, and as a consequence, most MIDI-to-micro packages rightly place most of the emphasis on the software provided.

Now, the sad truth is that most currently-available MIDI composition programs are unfriendly in the way they allow the user to access MIDI control options, and usually fall short of full implementation. I suspect this is mostly because each supplier wants to be first in the music shops with product of some variety, leaving us with bland and unhelpful programs, hastily re-hashed from test software, and an 'It'll do for now and our next package will be amazing' story.

Software development almost always lags far behind hardware, but in this case there are a lot of knotty timing and memory management problems involved as well. It's a highly skilled task to design friendly programs that allow composition on a number of polyphonic tracks, especially from real-time synth keyboard inputs (surely the most attractive method to the majority of musicians?), and even if these problems are overcome and your megaprogram works, the resulting code will take up a large chunk of precious RAM, severely limiting the amount of MIDI 'event' data that can be stored - a major drawback for anyone interested in writing complex and lengthy pieces of music.

Roland are well aware of these problems, and their answer is the MPU401 MIDI Processing Unit. The MPU contains an eight-bit processor, 2K of RAM (for its own use), 8K of ROM, and specially-designed VLSI gate arrays that take care of all the protocol involved in transferring data between computer and MPU. The ROM contains a control program that manages information held in tables (using the 2K of RAM) to account for real-time MIDI event data on eight polyphonic tracks, timed by the MPU processor. The bottom line to all this is that data is transferred between host and MPU on interrupt to the host processor so that many host functions, notably screen handling and disk I/O, can carry on while the MPU plays back or records event data. So, data can be saved and loaded as required, allowing your compositions to use as many events as your disk system will store.

Hardware

The MPU is supplied in a light grey metal box about 7½" x 4½" x 1½", and weighs approximately 1½lb. At the front edge are seven sockets - MIDI In, MIDI Out 1, MIDI Out 2, Roland five-pin DIN Sync out, and two jack sockets for FSK tape synchronisation (in and out). At the rear is a 25-pin 'D' connector for communication with a micro through the relevant interface. These interfaces seem unnecessarily expensive (approximately £70), as it appears that you need only connect the 'D' type socket's eight data lines, three address lines, Read, Write, Reset, DSR and Chip Select to the relevant pins on the parallel user port of your computer. Also required are 5V, 150mA power supplies (probably) available direct from the user port. It'll be interesting to see if anyone comes up with low-cost alternatives to this arrangement.

Note that three address lines are provided where normally only one would be expected. The extra two lines allow one host to run up to four MPUs using polled interrupts, giving access to 32 tracks and 64 Channels of MIDI! However, before commenting critically on this prospect, I'd like to see them all actually working.

Removing four screws gets you inside the box, revealing a tidily laid-out PCB containing ancillary chips, connectors and so on, plus a 6801-family processor, the square chip containing the VLSI gate arrays, a 2764 ROM and a 6116 RAM. Also included is a tiny metronome 'beeper' to allow count ins to be employed independent of external instruments.

"The extra two address lines allow one host to run up to four MPUs... giving access to 32 tracks and 64 Channels of MIDI!"

Software

MRC is the eight-track real-time composing program that was shown working on an Apple II + MPU at the recent British Music Fair. Although Roland insist it will be available from launch, there are no operating instructions in this country as yet, and poor old Rick Cannell of Roland had to figure it all out for himself.

Happily, MRC is an excellent example of a user-friendly program: all features are selected from a simply laid-out, single screen menu arrangement by moving a cursor (using the I, J, K & M keys). Placing the cursor over a required feature and pressing Space or Return either selects a function (such as PLAY or RECORD), or allows you to specify a value, as for TEMPO Up/Down or TIME SIGNATURE, which is then displayed on the lower half of the screen. Helpful touches are the straightforward track selection (any track, any channel, any time), the 'percentage memory used' chart at the bottom of the display, and the efficient use of the MPU's timing facilities (far better than standard MIDI) to provide auto-correction to 4th triplets, 4ths, 8th triplets, 8ths, triplets, 16ths and 32nds.

However, only the minimum number of facilities for simple composition have been included, and I hope we can look forward to some more complete packages in the future. Still, it's an excellent start.

Armed with the relevant function values, anybody who has used a multitrack recorder should get the hang of MRC very quickly, though it's a shame the MPU provides no aid for step-time input, as MRC with an editing facility would be a versatile program indeed.

Conclusions

It's very hard to fault the philosophy behind the MPU401. MRC, the computer I/F and the 401 itself are expensive as MIDI outfits go, but the relative simplicity of the software and the interrupt-driven operation offer something well above the norm.

As far as musicians are concerned, the choice of IBM PC and Apple as the first available incarnations is a poor one, and it's strongly in Roland's interest to introduce home micro options in the near future: no doubt other companies will oblige very shortly. As always, the main problem is lack of software, especially given the Roland approach of encouragement as opposed to direct supply. I hope they ensure that suitable packages appear, and assuming they do, all I need to know about them is when, because as soon as they're available, I'll buy one!

RRPs: MPU401, £160; computer I/F connector, £70; MRC software, £50. All prices are inclusive of VAT, and further information is available from Roland UK, (Contact Details).