Modern MIDI Sequencing

Feb 1, 2000 12:00 PM, Scott R. Garrigus

For more than 15 years, MIDI has exerted a tremendous influence on all types of music making. One of the most fundamental applications of this technology is recording, storing, and manipulating sequences of MIDI messages that represent all sorts of performance gestures-such as playing specific notes with specific durations and volumes, stepping on a sustain pedal, moving a pitch-bend wheel, and so on. This is performed by using a MIDI sequencer, which can be a dedicated hardware box or a software program running on a computer.

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A basic MIDI-sequencing setup might be a MIDI keyboard and a computer with a MIDI interface running a sequencer application. MIDI cables connect the MIDI Out from the keyboard to the MIDI In of the computer's interface, and also connect the MIDI Out from the interface to the MIDI In of the keyboard. (An even simpler setup consists of a single keyboard workstation, which includes a built-in sequencer.)

Such a setup lets you record and play your performances on the keyboard. It also lets you change the performance in many ways. For example, you can change a note's length or Velocity; move it to a different rhythmic location; or manipulate Volume, Pitch Bend, Aftertouch, Modulation, or Program Change. Whatever MIDI data you record, you can change. Of course, how useful this is depends on the sophistication of your sequencing software or workstation's sequencer.

Typical sequencing software can display the recorded MIDI data in several different ways, including a tracklist, event list, and piano roll. Many also provide standard-notation displays (see Fig. 1). Each view gives you a different way to display and edit the same data. An event list lets you edit single MIDI events with precise numerical accuracy. It also gives you access to System Exclusive and other nonperformance MIDI data.

A piano roll provides a graphical representation of note and controller data, so you can easily edit the expressive qualities of your music, such as crescendos and diminuendos. A notation display lets you change your music by dragging and dropping notes on a virtual staff page.

These common tools barely scratch the surface, though. Most sequencers also give you the power to manipulate MIDI data in more global ways, including quantization, real-time processing, virtual routing, and synchronization. In fact, today's sequencers provide so many features, you might be missing out on some of the more complex but very useful ones.

IN THE GROOVE
A real-time MIDI performance is not always as accurate as it should be. As you play, you're likely to perform some notes slightly before or after their intended rhythmic position, or hold some notes longer or shorter than you mean to. A sequencer's quantize tool can alter the timing and durations of your recording so they fit a specified time grid with fixed intervals.

For example, you might apply a 16th-note grid to a run of sloppily played 16th notes: any misplaced notes move to the nearest 16th-note timing interval. Those notes then play back with perfect timing (unless a note is so early or late that it falls closer to a note before or after the intended location in the grid, in which case it is moved to the wrong rhythmic position).

Applying this sort of strict quantization results in very precise, mechanical rhythms, which is fine for certain types of music. But if you want your music to retain a more human feel, see if your sequencer includes a groove quantize feature. Groove quantization uses a time grid based on a prerecorded rhythmic pattern-called a groove pattern-rather than fixed intervals. A groove pattern might simply contain timing information, making it compatible with different sequencer programs. Or it can be a proprietary format-such as Cakewalk Pro Audio's native groove format-containing information on timing as well as on note duration and Velocity.

Basically, groove quantization works by imposing the timing, duration, and Velocity values of one piece of music onto another. For example, suppose you record a melody that sounds a bit too mechanical, but your bandmate slams out a really kickin' MIDI bass line that has just the feel you want. You can copy the bass track and use it as a groove pattern to quantize the melody track. This will impose the feel from the bass line onto the melody without changing the pitch of the notes.

This is just one of the many uses for groove quantization. Most of the groove-quantization tools (and straight quantization tools) give you control over how much influence a groove pattern or grid has over the data you're quantizing. You specify (as a percentage) how much the timing, duration, and Velocity of the notes will be affected (see Fig. 2). This lets you correct off-tempo tracks, add complex beat accents to each measure, synchronize rhythm and solo tracks, align badly timed tracks to one with good timing, and steal the "feel" from tracks as discussed earlier.

As a matter of fact, groove quantizing has become so popular, companies now sell groove-pattern files that let you steal the feel from tracks that have been recorded by professional keyboard, drum, and guitar players. It's almost like having Steve Vai play on your latest project!

REAL-TIME PROCESSING
Some sequencers let you process MIDI data only offline. If you want to quantize a track, scale a group of Velocities, or filter specific types of events from a track, you have to do it when the music isn't playing. Also, the selected MIDI data is altered destructively.

Real-time processing lets you change the MIDI data while it plays, but it doesn't actually alter the data. This type of processing might be found as a plug-in, such as the MIDI Effects in Cakewalk Pro Audio, or integrated directly into a program as it is in Steinberg's Cubase and Emagic's Logic Audio. Real-time MIDI processing is typically nondestructive because it doesn't change the recorded MIDI data; it just affects the stream of data that's being played back.

Some of the types of MIDI processing you will find are effects for quantizing, adding echo and delay, rechannelizing, filtering events, time stretching, adding arpeggios, analyzing chords, and changing note Velocities. It's usually possible to experiment with numerous types of settings, and you don't have to worry about your data being irreversibly altered in the process. For instance, you can easily try out many different quantization values as you listen to find the one that works best. Then, if you want, you can permanently apply the effects to your data, just as you would with any other editing command.

Cubase VST offers yet another type of MIDI processing: its MIDI Processor function allows you to apply MIDI effects not only to data you've recorded but to live input as well. And even more features are available in Logic's Environment window, where you can design complex "networks" of processes that alter MIDI data in numerous ways. If you prefer, you can use one of the numerous user-created Environments available from Logic-based Web sites, such as Lynn Sasso's at www.swiftkick.com.