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Yamaha MEP4 Processor | |
Article from Electronics & Music Maker, June 1986 |
Simon Trask somehow finds time to examine the most sophisticated MIDI event processor of the lot. Are its facilities usable?
Yamaha's MEP4 is the most comprehensive MIDI processor yet devised. Its black-box exterior conceals a wealth of facilities to manipulate MIDI data, but are they sufficiently easy to use to be worthwhile?
Figure 1 shows the basic layout of the MEP4. Four independent processors receive data from the single MIDI In, and can send the results of their own operations to any one of four MIDI Outs; the Thru fulfils its normal role of passing on incoming data unchanged, which means you could, for instance, chain two MEP4s together. As well as directing the output of each processor to a separate Out, you can route up to four processors to one Out, allowing the creation of composite effects.
What you can't do is send the output of a particular processor to more than one MIDI Out, so if you want to layer an effect, you have to double the effect on two processors or daisy-chain your synths.
But what are these enigmatic processors? Figure 2 illustrates the components that go to make up each processor: remember there are four of these running in parallel, each with its own settings of the same parameters. Each processor can be switched on and off from dedicated front-panel buttons, which is a useful way of removing a particular instrument from the action, or of isolating part of a composite effect.
Starting at the left-hand end of the diagram, the Channel Filter allows you to assign a processor to any number of MIDI channels, from one up to the full 16. At the other end of the chain, the Output Assigner allows the result of the processor's actions to be sent on any single MIDI channel, and/or offset from its current channel number by a constant amount, and then sent to any one of the four MIDI Outs.
It's worth bearing in mind that the MEP transmits its processed MIDI data on a maximum of four MIDI channels; should you require further channel capacity (which you may well do if you're using multi-timbral synths or samplers), you'll need a second MEP4 connected via the Thru.
The Data Presetter allows you to select a patch number, pitch-bend value and two controller-code values, which are all sent on the selected MIDI channel whenever a new MEP4 program is called up. Thus, you can trigger up to four different patch numbers, on any channels, for every incoming patch number. This is the same facility offered by Dynacord's MCC1, but with the added advantage that MEP4 memories don't have to be aligned with specific patches - more on this later.
The pitch-wheel setting is perhaps most useful for zeroing the effect of the wheel, while Yamaha's examples commonly use the two controller codes for zeroing the modulation wheel and setting the volume pedal to maximum. Resetting controllers is a useful task, and it's a pity Yamaha haven't allowed for a few more of these codes to be transmitted.
However, what is useful is that the MEP4 transmits sustain pedal-off messages together with note-off messages for all notes currently active, in a healthy variety of circumstances including whenever a new program is selected or a processor is turned on or off.
All of which should ensure you don't get droning notes at any time when using the MEP4 - a reassuring thought.
The Message Filter allows you to filter out any of nine categories of MIDI message from the data stream. These are: note-off, note-on, polyphonic aftertouch, control changes, program changes, channel aftertouch, pitch-bend, channel mode messages and system messages. Aside from choosing which data goes to which slave instruments during performance, you can also use this section as a means of removing unwanted data (say, pitch-bend data) from a sequencer track.
The Delay Processor allows you to delay transmission of all MIDI data passing through it for up to three seconds, selectable in millisecond increments. Like Akai's ME10D MIDI Digital Delay (reviewed E&MM November '85), this is only a single delay. But unlike the Akai, the MEP4 allows you to group all four processors together for a single four-note delay - still within the three-second limit. This makes the delay quite flexible, but the MEP4's routing limitations mean you can't send the composite effect to more than one MIDI Out. Pity.
I've left till last what is probably the most flexible and currently unique aspect of the MEP4: the Data Modifier. Unfortunately, this is also the section in which you come most intimately into contact with actual MIDI data, so you really need to know about MIDI if you're not to get lost.
With the Data Modifier, you can alter any MIDI messages (one per processor) apart from channel mode and system messages, in up to four ways. 'Altering' can mean anything from changing a particular value to changing the entire message. And you can convert messages which have specific data values, so that one particular note, for instance, can be used to trigger any result the MEP4 is capable of creating.
There are six ways in which you can modify a message (and remember you can combine them in up to four steps): Expand, Step, Offset, Reverse, Limit and Convert. The first five of these modify data bytes only; Convert is the one that allows you to change a message completely.
"Presentation: When you disentangle the MEP4 from its packaging, you discover program charts and system setups for all 30 presets — which are invaluable"
Expand allows you to multiply a data value by any value from 1/16 to 16. This could be a useful way of, say, altering the velocity range of notes on a particular channel.
Step allows you to filter particular messages whose data byte isn't a multiple of a specified value, which could come in handy for cutting down on data generated by continuous controllers.
Offset allows you to add a fixed value (-127 to +127) to any data byte. The most obvious use for this is to create parallel octave, fifth or fourth effects - though any interval is possible.
Reverse allows you to reverse MIDI data for any specified message around a selected fixed middle-point. You could use this, for instance, to crossfade between two instruments (which would require more than one processor), or to create reverse keyboard effects á la Zawinul Prophet 5.
Gear in this article:
MIDI Utility > Yamaha > MEP4
Review by Simon Trask
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