MIDI By Example (Part 3)
It's a matter of merging
Merging two sets of MIDI data simultaneously demands a little intelligence...
Last month, we looked at how you could alternate between two MIDI Controllers by using a MIDI Switcher, a relatively cheap device due to its passive circuitry and simple design. In passing, it was mentioned that such a device would not allow you to have two MIDI Controllers active at the same time. This is a job for a MIDI Merger.
While it may appear that a MIDI Merger is a relatively simple device for combining the MIDI information from two MIDI Outs, its design actually calls for the use of a microprocessor. The reason for this is that MIDI messages often consist of two or three parts and it is important to ensure that these are kept together. If they are not, the message becomes garbled. The MIDI Merger, therefore, has to be an intelligent device and as such costs far more than a MIDI Thru box or Switcher - typically around £80 for a two-into-one unit.
There are a number of situations which call for the use of a MIDI Merger. Let's look at a couple of examples. The first is where you need to share a sound module with another musician, each of you playing your own MIDI Controller. This is illustrated in Figure 1. For the sake of simplicity, two keyboards are shown, but really, they could be any type of MIDI controller - drum machine, guitar synth or wind controller - as long as they are capable of transmitting MIDI information from a MIDI Out port. The best results here will be with a multitimbral sound module which can play different instruments on different MIDI channels, and a pair of Controllers which can each be set to transmit on a separate MIDI channel.
Another situation requiring the use of a MIDI Merger is when editing the tones in a sound module using a visual editor on a computer. A two-way link between the computer and sound module needs to be established so that the computer program can request, and receive, information from the module. However, a keyboard also needs to be attached so that the edited voices can be played.
Figure 2 shows how this is set up and how a MIDI Merger is connected into the system: the MIDI Out from the keyboard is merged with the MIDI Out from the sound module and then sent to the MIDI In of the computer. The visual editor is likely to have a 're-channelise' facility so that the notes coming in from the keyboard can be set to the MIDI channel of the sound currently being edited in the module - an important point when working with a multitimbral module.
Next month, MIDI By Example begins its examination of synchronisation with a look at how sequencers and drum machines may be linked together.
Feature by Vic Lennard
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