As any master carpenter will tell you, before you start any project you need to figure out what's the best tool for the job. Today's technology gives musicians a lot of options. If you've been making electronic music for only a few years, you may have jumped straight into digital audio with sampled loops and plug-in effects. Those are great tools, but there are times when plain old-fashioned MIDI sequencing will give you much more expressive control over your music. If you've never used the MIDI features of your multitrack recorder, you've come to the right place. In this column, I'll explore how a computer (or a standalone workstation) records and plays MIDI data. I'll also discuss the main ways in which you can edit the data to clean up and personalize your recordings. MIDI recordings are much easier to work with than digital audio recordings. That is because MIDI tracks contain only performance data, not actual sound. In order to listen to a MIDI track, you have to send it to a MIDI sound module, such as a synthesizer or sampler, which responds to the data by playing notes. MIDI data is very efficient: a single Note On message, which occupies only a few bytes of computer memory, can trigger a sound that's many seconds in length. Even an old, slow computer can record and play dozens of MIDI tracks at once with perfect timing. The downside is that a Note On message contains no information about what the actual sound will be. The same message could trigger a flute note or a sampled explosion. Or, if the synth on the receiving end isn't powered up, the Note On could result in no sound at all. It's up to you to make sure MIDI playback produces the desired sounds. The following discussion applies to any MIDI sequencer, whether it's a computer program or a sequencer built in to a workstation keyboard. If you're not clear about the various types of MIDI messages, refer to “Square One: MIDI Me” in the July 2003 issue of EM (available online at www.emusician.com). WHY USE MIDI? If a sampled loop has exactly the sound you want, there's no need to mess with MIDI. MIDI is the tool of choice when you need to fine-tune the details of a performance. With a MIDI sequencer you can: • Add filter sweeps and other expressive gestures to a line or just a single note using Control Change messages. • Change the feel of a drum pattern, subtly or drastically, by changing the timing of MIDI events. • Create your own beats by triggering individual percussion sounds. • Try a different lead, bass, or electric-piano sound while keeping the performance (notes and rhythms) exactly the same. • Change the tempo or transpose a whole song to a new key with absolutely no loss in audio quality. Though you can use MIDI tracks and sampled (prerecorded) loops or other digital audio in the same piece of music, it's difficult to change the rhythm or tone color of a sampled loop by editing MIDI data. There are some ways to do it, but discussing them would take us well beyond the scope of this article. THE BIG PICTURE Most sequencers record MIDI data into tracks, which run horizontally across the computer screen in the track or arrangement window. Usually each track is assigned to a single MIDI channel. During playback, all of the track's data is transmitted on that channel, and any synth assigned to that channel will respond to the data by playing the notes recorded in the track. If you don't want to listen to a particular track, you can click on its mute button. It's important not to confuse tracks (a sequencer feature) with channels (a MIDI feature). In most sequencers, it's easy to assign several tracks to transmit on the same channel. For instance, when building up a MIDI drum part, I often put the kick and snare on one track, the hi-hat part on a second track, and crash-cymbal hits on a third track. All of the tracks transmit on the same channel and are played by the same drum module. By doing this, I can copy and paste a cool hi-hat pattern without having to mess with the kick and snare. Conversely, you can often find a track setting called Any, which allows a track to transmit data on more than one channel. You can then put data that has several different channel assignments into a single track. Usually there's no reason to do this, but most sequencers will allow it. With a few exceptions, each MIDI message has its own channel assignment. This channel will be overridden by the track's channel assignment unless you set the track to Any. The MIDI output channel is just one of the playback settings you can make for each track. The most important settings for tracks are listed below. Transposition By moving each track (except the drum tracks) up or down in half steps, you can play the music in a different key. By transposing a single track up or down by 12 half steps, you can hear the part in a different octave. Volume When playback starts, each track can send a MIDI Control Change 7 (Master Volume) message. A synth assigned to that channel will adjust its output volume based on this message. This is a quick way to set up a rough mix for a MIDI-based song arrangement. Program Change When you select a Program Change message (and, if need be, a Bank Select message) for the track, the sequencer will send out these messages on the track's channel just before starting playback. This ensures that each synthesizer will have the proper sound selected. Velocity scaling MIDI notes all have Key Velocity values, which can be anywhere from 0 through 127 (though the values you will see in your sequencer are from 1 through 127). In most synths, Velocity is used to make the sound of each note louder or softer. Adjusting all of the Velocity values for a track up or down is another quick way to bring the sound of a synth forward in the mix or reduce it so it blends in better. Velocity scaling is a better choice than Master Volume when you've assigned several tracks to the same MIDI channel, because Master Volume is a global message that will be applied to all of the sounds played by the synth on a given channel. Velocity data is attached separately to each note. With Velocity scaling, for instance, you can boost the level of the hi-hat without affecting the kick and snare on the same channel, as long as the hi-hat is in a separate track from the kick and snare. SEQUENCE EDITING Changing the track playback parameters is a quick, easy way to change the sound of a MIDI sequence, but you can go much deeper. Most sequencers offer several types of editing utilities and editing environments, with which you can bend, shape, mangle, and torment the MIDI data. The editing facilities in workstation sequencers tend to be simpler than those in computer-based sequencers, but some workstation sequencers are quite powerful. Consult your owner's manual for details. The most important types of editing are: Track window drag and drop The track window will allow you to separate MIDI data into short segments (variously called chunks, parts, or clips). You can drag these segments to an earlier or later position in the composition, delete them, and copy them. After improvising a 32-bar bass line, for instance, you can separate out the 2-bar phrase you like best using a scissors tool, delete the rest of the take, and copy the 2-bar phrase over and over for the length of the song. Piano-roll display In
the piano-roll window, MIDI notes are displayed graphically. The
display looks rather like the rolls of paper used in player pianos,
except that it runs horizontally rather than vertically. Time
runs from left to right, so longer notes appear as longer lines
in the display. Pitch runs vertically, with high MIDI notes at
the top and low ones at the bottom. The
tool for micromanaging your MIDI data is the event list. Here
you'll see a list of all the data in a track, and you'll be able
to edit each event (note, Control Change, Program Change, and
so on) as desired. For instance, you can lower the Velocity of
a single note that you hit a little too hard, shorten a long note,
or change the pitch of a wrong note without disturbing its timing.
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