Students in music-technology labs often learn keyboard skills and technology skills simultaneously. As a result, they tend to make many mistakes when creating their first keyboard-based MIDI sequences. In the April/May 2005 “Tips and Techniques” column, I described techniques for using quantization to correct rhythmic inaccuracies. I pointed out that quantization can be a mixed blessing, and that overusing it can remove an expressive element of musical performance.

In this column, I will discuss two other ways to correct note rhythms: rerecording and note editing. Understanding the differences between those techniques will allow you and your students to edit your MIDI tracks in the most efficient manner possible.

FIG. 1: Sonar’s loop-recording feature can automatically store each take in a separate track without stopping. Here we see four takes generated by playing along with a four-measure loop. Each take can be soloed to determine the best performance; in this example, take 3 is soloed

One way to correct a track that contains multiple mistakes is to erase it completely and try again. Some teachers encourage this brute-force solution because it helps students develop keyboard technique. If, however, the goal of the lesson is to complete a MIDI sequence, it's easier to correct the mistakes by rerecording only the portions with the mistakes.

A common way to accomplish that is to use a sequencer feature called punch recording, or punch-in, which allows you to rerecord a user-defined section of the track. Most software allows you to set the punch-in and punch-out points (or locations) anywhere within a measure or group of consecutive measures.

When recording a punch-in, it helps to start playing along with the music before the punch-in point and to continue playing after the punch-out point. For example, if the punch-in occurs in measures 9 and 10 of a track, start the sequence playback at measure 6, start playing the keyboard at measure 8, and play through to the end of measure 11. That will make the punch-in less obvious by maintaining the flow of the musical line. You can undo and repeat the punch-in process as needed until you are satisfied with the edit.

Some software automates that process by allowing you to set preroll and postroll playback boundaries, in addition to punch-in and -out points. The preroll is the time between the beginning of playback and the punch-in point, when recording begins; postroll is the time between the punch-out point (when recording stops) and the end of playback. The terms come from the heyday of analog recording, when the term rolling tape meant that the tape transport was in motion.

Another rerecording technique for correcting part of a MIDI track is called loop recording. With this feature, you can record as many takes as you like and have each take automatically saved on a separate track. Loop start and end times are set just the way punch-in and -out points are. This is a great way for students to improve their keyboard technique; they can keep replaying and rerecording a part without stopping until they get it right, without losing any of their takes (see Fig. 1). Later, the students can compare their takes and decide what to keep.

Some software lets you combine loop and punch recording to record several takes of a punch-in. For example, you could loop measures 6 through 11 in a track, and set the punch-in to begin at measure 8 and to end at measure 10.

If you want to correct the rhythms of only a few consecutive notes in a track, it is simplest to rerecord only those notes by using a recording mode called Overdub (sometimes called sound-on-sound). Overdub mode allows you to record new data on a track without erasing existing data. Unlike loop recording, however, all of the data is layered on to the same track.

To use this feature you must first erase the notes with the mistakes, and then rerecord only the erased notes. This is a simple technique that can be used by very young students:

1. Identify and select the wrong notes, and lasso them with the mouse.

2. Erase the notes.

3. Check that the recording mode is set to Overdub.

4. Start the music one or two measures before the missing notes.

5. Play the correct notes.

If a student makes a mistake, he or she can click on the Undo button and try again.

If you punch-in/out or overdub to rerecord a part, here are two tips that might save you time:

1. Record the part in small sections instead of trying to get through the entire part in one pass.

2. Slow down the song tempo during recording; a tempo decrease of 25 percent can make a difficult part much easier to play.

It's easy for students to fix pitch errors in a MIDI track graphically, using either a piano-roll display or a notation display. Editing rhythms and articulations graphically is a little trickier, but it can be done. There are four ways to alter a note's rhythm and articulation: move the starting point back in time, move the starting point forward in time, shorten the duration, and lengthen the duration.

FIG. 2: A momentary sounding of two notes is a common giveaway when emulating a monophonic wind instrument. In 2a, the duration of the first note is too long and carries into the start of the second note. This error is easily fixed by using the mouse to shorten the first note’s duration (2b).

In the piano-roll view, you can use the mouse to slide or “nudge” the start point and the duration of individual notes. If a note was played late, you can make it play earlier by sliding the note to the left. If a note was held too long, you can shorten the duration by clicking on the end of the note and sliding to the left. Nudging sometimes can be all that is needed to correct the rhythm or articulation of a few notes (see Fig. 2). Note that most software has a Snap to Grid feature that allows you to move note start times and durations to a user-defined value such as an 8th note or a 16th note. If you don't want the track to sound metronomic, check to see that this feature is disabled before attempting to nudge.

Note start times and durations also can be edited by using the MIDI event-list display available in most sequencing software. The event list shows timing information for every note as numeric values. This display can be intimidating to most students, however, and is more appropriate for use in an advanced sequencing class.

Be sure to listen closely to the result of your edits. If you soloed a track in order to hear it more clearly, be sure to unsolo the track and listen to your edits in the context of the ensemble. It doesn't matter how bad the soloed track sounds; what matters is the total sonic effect of all of the tracks playing simultaneously. That's why I often edit tracks without soloing them: if I can't hear anything wrong, I don't care what's on the track. The sound of the music is the bottom line.

For information on Don Muro's books and music, visit www.donmuro.com.