MIDI and the Mac
Part 3
The Advantages of MIDI
MIDI has been a great benefit to electronic music in the sixteen years since its birth. It was a rare example of cooperation over proprietary standards, an example that the computer industry should follow more often. MIDI made software-based sequencing possible, as well as software-based patch editing and SMPTE synchronization with MIDI Time Code. The separation of controllers and sound modules, always a part of synthesis, has opened the door to new musical experiences. Percussionists, guitarists, wind players, and even dancers can play the same instruments (or the same sound modules at least) as easily as the more traditional keyboardist. The sequencer (itself as powerful as the computer it runs on) led to the multi-timbral module, which led to General MIDI. The standardization of General MIDI coincided with the initial growth of the Web. The two combined made it possible for musicians to easily distribute MIDI files over the Internet.
The Limitations of MIDI
MIDI is a serial bus. This is its most fundamental limitation. We conceive of musical events as occurring either simultaneously (chords) or sequentially (melodies). In MIDI, all events are sequential, right down to the individual zeros and ones that comprise each message. Not only does the status byte comes before the data byte, but the first bit of the status byte (its identifying bit) comes before the others. So even a single Note On message, which we think of as one event, is actually 12 bits. The bandwidth of MIDI (31,250 bits per second) seems fast enough to track a single keyboardist. But what about a keyboardist with a volume pedal, pitch wheel, and breath controller? What about a multi-track sequence of notes, control changes, and pitch bend recorded by this keyboardist?
MIDI transmits like a modem, but the timing is far more critical. Lags on modems are frustrating, but when the data isn’t meant to be received in real-time, the wait is merely an annoyance. Music, though, has to be tight. The slightest lag will wreck the feel of an otherwise good ensemble, just like a musician dragging in a band. Even delays of milliseconds can change the sound (flanging—the whooshing effect used on many guitar tracks—is caused by a delay of only a few milliseconds). In addition, a sensitive musician produces many subtle changes in the timbre of an instrument while playing it. These subtleties are impossible in MIDI—there’s just not enough bandwidth.
Running Status
The MIDI specification includes a clever trick called running status. Instead of sending a complete Note On message for every note in a chord, a controller sends a single Note On status byte, then the two data bytes that correspond to each note. If the chord contains four notes, the module receives seventy-two bits, instead of ninety-six bits. Running status extends beyond chords, though. As long as no other types of messages (control changes, patch changes, etc.) are sent, a single Note On message can define a collection of chords and/or melodies. This is the advantage of using a Note On message with velocity zero in place of a Note Off.
Filtering
Pitch bend is the most bandwidth-hungry message type in the MIDI specification. As you will recall from Part One, pitch bend uses two data bytes to represent a total of 16,384 values across its total range. Depending on the interval you have mapped to the wheel (an octave, a fifth, a major second), you probably won’t need all these values in order to make the changes seem continuous. Once you record the pitch wheel in a sequencer, you can filter out a certain amount (this is sometimes called “thinning”) and save bandwidth for other tracks. Real-time filtering is also possible. For example, MAX contains an object called “speedlim” that passes information through at specified time intervals. For example, you could set “speedlim” to 50 milliseconds, and numbers would only pass through at 50 millisecond intervals. Similar input filters are available on sequencers, though these usually pass a percentage of information through regardless of the speed the information enters the system.
When is MIDI not Really MIDI?
Last month, I discussed available software, focusing one paragraph on software “modules.” Though these instruments appear in the sequencer window on a MIDI port, just as hardware does, this is an illusion. The MIDI “cable,” in this case, is a virtual connection between two software programs, one a sequencer and the other a synthesizer or sampler. If this virtual connection is possible, then what would stop me from connecting two other types of applications? All I need is a bus. As luck would have it, this bus, the Inter-Application Connection (or IAC) bus, is standard with OMS. I have worked a lot connecting various versions of Vision (Vision, Studio Vision, Vision DSP) with MAX (my beloved interactive programming application). Now I’m even more excited about connecting MSP (MAX’s digital audio twin) and building my own instruments and effects. The connection, though, is still limited arbitrarily by the bandwidth of MIDI, which is far less than the 100 MB bus of my G3. It’s the first place where an actual increase in bandwidth is possible.
New Connections, New Possibilities
Connection speed between computers is also increasing. The old serial buses could accommodate multiple MIDI channels, which made MIDI interfaces like the Opcode Studio 5 and the MOTU MIDI Time Piece possible. USB can handle a much higher bandwidth, but MIDI interfaces are lagging behind. The USB MIDI Timepiece has the same number of ports as the serial version (eight each) while the Opcode MIDIPort 96 accommodates less than half the ports of the Studio 5 (six instead of fifteen). The one change has been in the area of USB audio interfaces, which I will cover in Part Two of my Digital Audio and the Mac Series (coming in issue 6.02, February 2000). Even higher bandwidths are possible through either Ethernet connections or FireWire. Sadly, neither of these technologies has been exploited, or even explored at this time.
The (Possible) Future of MIDI
The development of MIDI divides into two tendencies. The experimental tendency is to push boundaries and achieve what is yet unachievable, and the commercial tendency is to standardize what is possible and make it cheaper and easier. These paths often cross, though, and are ultimately dependent on each other.
Sequencing, multi-timbral synths, and non-keyboard controllers were forward-reaching ideas brought into the mainstream. General MIDI, in contrast, was all about ease of use, but it helped bring MIDI to the Web. These paths will continue to cross, and sometime in the near future, MIDI itself will be replaced by something far more advanced. My guess is this something will be related to network technology, which is now very cheap. It will allow a musician to control an electronic instrument (or an ensemble) with all the subtleties of an acoustic instrument. It could also merge at points with the Internet, leading to online jams between musicians and audience members (if the distinction is even relevant). Composers, songwriters, bands, and performance artists already place samples of works on the Web (often as MP3s). In the future, they might create more works specifically for the Web.
Conclusion
MIDI and the Mac have been with us for about the same amount of time. Both have opened up areas of electronic music that were previously unthought of, impractical, or prohibitively expensive. Times change, though, and so must technology. The Mac OS we’ve all grown up with will soon be supplanted by OS X, and perhaps it’s also time for MIDI to yield to a more advanced musical networking system.
Correction
Last month’s installment (Part Two) was incorrectly titled “What is MIDI?” That topic was covered in Part One. Part Two was a obviously a review of hardware and software. I should have caught this before the issue got posted, but I lost e-mail contact in a critical time window that happened to coincide with my upgrade to OS 9. It was pilot error (i.e my mistake), not a bug.
Addendum: I Almost Forgot the PowerBooks
In theory, PowerBooks should perform the same as their desktop counterparts. Some individuals have had problems, though, and some wise advice has been posted on the PowerBook Zone. To summarize, be thorough. Install all the software you need and be sure to remove any conflicting drivers.
References
There is a large amount of information about MIDI and related topics available on the Web. Here’s a small sample to get you started.
- Electronic Music Interactive: A collaboration of Future Music Oregon and the New Media Centers. It has received many excellent reviews.
- A MIDI Tutorial: An overview, which overlaps somewhat with Part One of this series.
- The Synth Zone: Extensive information on synthesizers.
- MacMusic: A large site dedicated to “Music, Audio, and MIDI on the Macintosh.”
Next Month: Digital Audio and the Mac: Part One of another multi-part series.
Copyright © 1999 David Ozab. David Ozab is a Ph.D student at the University of Oregon, where he teaches electronic music courses and assists in the day to day operation of The Future Music Oregon Studios
. You can visit his Web page at
http://darkwing.uoregon.edu.
Also in This Series
- Part 3 · December 1999
- Part 2—What is MIDI? · November 1999
- Part 1—Introduction · October 1999
- Complete Archive
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