Despite the blinding speed of technological progress, 21 years after its birth, the MIDI standard is still heavily in use — a testament to its strength of concept. In a previous column (“MIDI on the Move,” August 2004), I opened up a discussion of MIDI, including its history and original purpose, and provided an overview of its use in modern computer-based studios. This column seeks to fill in the outlines with a bit more color. Is your studio nothing more than a laptop packed with music apps? Don't own a MIDI interface? Think you don't need to know about MIDI? Think again.
A good example of where MIDI is implemented in the virtual studio is with the ever-more-popular ReWire protocol. For example, say you like to compose raw tracks with Propellerhead Reason, but you prefer to mix with Apple Logic. You like the drum machine in Reason, and you dig the synths, but the built-in effects just don't cut it for you. If you would rather use your Logic, Audio Units or VST effects with your Reason tracks, it's definitely possible. Just select a stereo pair of audio tracks in Logic, set them to ReWire Mix Left and Mix Right, respectively (or any of the 64 ReWire channel streams available), and let the audio from Reason stream right in.
But what if you don't care for Reason's sequencer and you want to go in the other direction: sequencing the Reason instruments from within Logic. Can this also be done? Indeed it can, by using ReWire's MIDI capabilities. In this scenario, you create an individual ReWire instrument in Logic's environment, and within the instrument, you choose an appropriate Reason ReWire bus. As with standard MIDI, each bus includes 16 channels numbered 1 through 16 and a setting for All (which corresponds to MIDI's Omni mode). Much of the grunt work is done for you; the various channels automatically get populated by each of the available instruments in Reason's rack, corresponding to the current song. The ReWire scheme, as with MIDI, is two-way dynamic: If you open up a different song in Reason, Logic's ReWire channels automatically update themselves on the fly to reflect the new modules. Perhaps the best part is that you don't need cables or a MIDI interface, but you still need to understand MIDI — and ReWire.
SO MANY CHANNELS
In case you are brand-new to all of this, almost all MIDI devices — whether they be sequencers, classic drum machines, rackmount sound modules, et cetera — function via 16 channels per port. In the case of hardware, this means that each physical MIDI jack is capable of either sending or receiving as many as 16 channels total. So, for example, if you are sequencing a sound module such as a Korg Triton Rack, you can assign 16 sounds to 16 different MIDI channels and sequence them simultaneously. Or if you have an 8×8 MIDI interface, that interface is capable of sending and receiving a max of 128 channels in both directions. This 16-channel protocol has been a stalwart almost since the very beginning of MIDI and is still a recognized standard.
In the case of software, most “MIDI” devices (such as MIDI tracks in DAWs) also can be assigned to any of 16 MIDI channels or to Omni. Although this is useful, it seems like a limitation. What if, in the previous example, your Reason songs use more than 16 different modules, but you still want to mix them all separately in Logic? Fortunately, in the land of software, multiples of 16 are often used, making the total number of simultaneously available channels limited mainly by available CPU resources. In the Logic example, if you are addressing more than 16 Reason modules, they simply spill over into the next available bus on the ReWire instrument. If you have a Reason song with 16, 32 or even 64 open modules (or any other odd number in between; it doesn't have to be multiples of 16), Logic can accommodate if your CPU can.
If you're interested in a good example of the interrelationship between MIDI hardware and software, just plug in any control surface to — you guessed it — Reason. If you go into Reason's basic MIDI preferences, the only available option is to set a single MIDI channel with which to address Reason's sequencer, thus making it appear as though the program is only one-part-multitimbral (meaning it can only be addressed by a single MIDI channel). This is not the whole picture. With a controller, you can remotely access most of the controls of the different Reason modules, each on its own MIDI channel. You do this via a MIDI Learn function that is found within the Edit MIDI Remote Mapping command. When Remote Mapping is engaged, you can click on any addressable control in Reason and select Learn From MIDI Input. Then, by turning any knob or moving any slider on your controller, that specific knob or fader will automatically be mapped to the selected control in Reason, MIDI channel and all. This means that by switching MIDI channels on your controller and selecting different modules in Reason, you can remote-map each module in the same fashion, with unique MIDI-channel assignments.
This second installment is still just a tiny primer on MIDI in modern times (one could write several volumes as thick as Tolstoy's War and Peace on the topic), but it illustrates how the MIDI standards have been adopted by audio applications while providing some insight into the inner workings of a select few. Although Reason is a good platform on which to learn basic MIDI if you don't already own any hardware, just about any multitrack, multitimbral environment or ReWire-compatible application will do.