The present generation of sequencers can be used to edit and synchronize both MIDI data and the data that constitutes actual sounds. This chapter is concerned with the editing of MIDI data.

A MIDI sequencer is a program that functions as a multihanded keyboard player and knob twister. It can play many of your synth's voices at once, provided the synth has a "multitimbral" mode. With it you can produce music with extremes of tempo, texture and dynamics.

The data in a sequencer is organized into tracks and channels as is a multichannel tape recorder. Sequencers often contain from 64 to 256 tracks. A track can be assigned to one of 16 MIDI channels. In some sequencers the channel assignment of a track can be changed through time.

A track can be manipulated in ways familiar to recordists. It can be muted, soloed, and looped. You can also "punch in" and "punch out," -- that is, you can re-record a portion of a track without disturbing surrounding material.

The track can be changed in additional ways. It can be transposed in pitch, offset in time, raised and lowered in volume, and shifted to the left or right through space ("panned"), provided the synth has stereo capabilities.

The length of the notes and their spacing can be tailored so as to occupy a specific time. This is also true for program changes, controller messages, pitch-bend and other MIDI commands.

Finally, the notes and their associated commands can be "quantized." Quantization rounds off the start-time and note lengths to a specified value such as a quarter-note.

As with a tape recorder, actions on one channel do not affect actions on another channel. Unlike a track on a tape, however, a track in a sequencer can contain control messages that affect volume and other parameters on the channel to which it is assigned.

If your sequencer and MIDI interface permit it, a track can be assigned to one of several MIDI-out ports. Each added MIDI port contains 16 channels so that you can make full use of more than one instrument without the data from one colliding with that from another.

A sequencer is to MIDI data what a word processor is to letters of the alphabet. Its editing menus manipulate two kinds of data. One kind applies to musical notes and the other to controlling the quality and articulation of an instrument's voices. You can insert such "registration" commands anywhere in the music.

Sequencers feature "local" and "global" editing commands. Local editing affects only one MIDI event at a time. Global editing affects every occurrence of an event throughout the whole piece or a designated portion of it.

When working with MIDI data, a sequencer records and plays music via MIDI commands that operate the instruments. It does not generate sound unless it can accommodate "wave" files, or other files that constitute actual sounds that are recorded and played through a sound card.

Many blind users are tempted to buy (or have bought) a synth that includes a built-in sequencer. Such a unit is compact and convenient for use in a performance setting where the equipment setup and musical arrangements are largely predetermined. However, if you have no access to the sequencer's display, or if it doesn't provide adequate auditory feedback as you make changes, you will not be able to edit precisely with it.

Although there are many sequencers that run on PC-compatibles, a lot of them employ graphics extensively and so are not suitable for a blind user.

The two most popular text-based sequencers are Voyetra Technologies' "SP Gold" and Twelve-Tone Systems' "Cakewalk." Both come in several versions, but even the most basic version can be used for serious composition. Upon request, the vendors will send you the manuals on computer disk.

Both sequencers provide all the operations that musicians expect and both provide good textual and auditory feedback for a blind user. They differ in the way the note-editing "field" is defined. SP Gold presents one complete track at a time. Cakewalk presents a grid of tracks and measures whose boundaries you define.

SP Gold employs many storage buffers for musical clips, but each buffer is limited to all or part of a single track. Cakewalk has fewer buffers, but each is a grid of user-defined tracks and measures.

Both programs handle "system exclusive" data used for modifying and storing patches. SP Gold always accesses this data from the patch librarian branch of the sequencer. Cakewalk allows "Sys-ex" data to be placed within the sequence itself.

Optimizing Your Screen Access -- When using a sequencer you will likely jump around the screen more often than you would in simple text editing in a word processor. You will find your screen access program's ability to define speech windows" and other customized settings very useful.

Watch out for computer overload when using speech output. Since MIDI instructions occur at a rate of 31.25 kilobaud, even a fast computer has a lot to do when processing music. The addition of speech processing can cause lapses in tempo and articulation. If you need to monitor some aspect constantly, define a window tailored to that particular piece of information.

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