One of the many benefits of teaching music in music tech labs is that students with little or no performance skills can record music that is in tune and rhythmically accurate. Since keyboard instruments do not require the performer to tune individual notes, students performing on electronic keyboards can play in tune from day 1. (I'm sure many elementary band- and orchestra directors can appreciate that benefit.) Developing rhythmic accuracy takes time, but when students record keyboard parts into a sequencer as MIDI data, the parts can be quantized to play back with 100 percent rhythmic accuracy.

Quantization is a mixed blessing: it can correct rhythmic inaccuracies but can also strip music of expression. (This lack of expression can, paradoxically, be used as a compositional element in certain types of contemporary music.) Brute-force quantization is easy to do; a third-grader can select a MIDI track and click the Quantize button. You and your students might find the results more satisfying, however, if you use some less destructive quantization techniques. Let's examine a proven approach.

First, identify the part that has the rhythmic errors. Sometimes a track can be rhythmically “off,” but the problem is not noticeable until another musical part is added. To find the mistakes, solo the suspect track and the beat source (a drum loop or metronome) together.

FIG. 1: When the notated music (1a) was recorded into a sequencer (1b), the first four notes were behind the beat, and the last four notes were ahead of the beat. Fig. 1c shows the result of quantizing the note-start times by 100 percent, producing a metronomic effect. Fig. 1d shows the results of quantizing the note-start times by 50 percent: the start times were moved closer to the nearest quarter note, but there is still some human-generated timing variance left in the track.

For best results, quantize as few notes as necessary. Today, virtually every sequencer allows you to quantize specific measures, as well as specific notes within measures. The adage “If it ain't broke, don't fix it” applies here: quantize only the notes with audible rhythmic errors.

In addition to quantizing individual notes in a track, you can also quantize the same beats or beat subdivisions in several tracks simultaneously. For example, if your song has a rhythmic unison section that is played by all of the parts, you can use the mouse to draw a box around the section in all of the tracks and quantize all of the notes in one operation.

Given a choice, use “soft” quantization. This variation is sometimes listed as the “quantization percentage” or “quantization amount.” When you quantize notes to the nearest eighth-note at 100 percent, every note will move to its closest eighth-note position in the measure. When you change the quantization percentage to 65 percent, however, the notes will move 65 percent closer to the nearest eighth-note position. Notes played close to the beat will be moved to the precise eighth-note position; notes played further from the beat will be moved closer to the beat but not precisely on the beat. This is a great way to tighten up note accuracy without producing the mechanical sound of 100 percent quantization (see Fig. 1).

When you use quantization, be sure to listen closely to the result. Depending on the type of music and the amount of quantization, notes before and after the quantized notes can sometimes sound wrong. If that happens, try using less quantization or try nudging the first few notes by ear to ease into the quantized section.

As stated earlier, quantization is a mixed blessing. While it can help beginning keyboard players of any age produce music with rhythmic accuracy, it can also remove an expressive element of musical performance. Sometimes you are better off avoiding quantization and fixing the rhythmic errors by either manually editing the notes one by one, or by recording a new track or portion of a track.

To give you a better idea of the sterilizing effect of quantization, listen to Web examples 1 and 2, which are available on the MET Web site (www.metmagazine.com). These two short .mp3 files are different versions of an excerpt taken from “The Journey,” one of the songs on my CD Reflections. The first file, “Journey1,” includes a piano solo, presented exactly as I played it. Listen for the deliberate slowing down of triplets, as well as for notes played behind and ahead of the beat. These time offsets, combined with the soft dynamic levels, help to give the solo a laid-back feel. “Journey2” contains the identical notes and dynamics, but the notes have been 100 percent quantized to 16th-note values. This version sounds stiff by comparison.

Finally, a more obvious approach is to give up on the problematic track or portion of a track and rerecord the part. Although that does not involve quantization, it is sometimes the easiest way to improve a performance.

There are a number of techniques that you can use to replace parts or all of a track, ranging from starting from scratch with a new track, copying an existing track and replacing just the problem measures (using punch in/out, for instance), and more. We'll cover some of those techniques in a future column.

Don Muro's CD Reflections can be found at www.donmuro.com. His music-technology lesson plans for the Expressions Music Curriculum is available from Warner Bros. at www.music-expressions.com.