The EM Poll

The Rite of Strings

Jan 1, 2007 12:00 PM, By Marty Cutler

           

A String of Polyphonies

Digital audio sequencers such as Apple Logic, Steinberg Cubase, and Cakewalk Sonar favor multichannel MIDI tracks. On the plus side, it is absurdly simple to record the individual MIDI output of all six strings. Editing is equally simple, especially if you color code the note display of the piano-roll-style window by MIDI channel. That way, each color will also represent one of the six strings (see Fig. 3). However, creating elaborate multitimbral setups as described for DP can be a convoluted affair.

FIG. 3: A single track in Steinberg Cubase SX3 can handle all six MIDI channels from your guitar. Fortunately, you can color code each MIDI channel and string in its Graphical Editor.

Setting up a multitimbral virtual synth is usually a relatively simple process; if your target instrument is not multitimbral, you can always load multiple instances of the instrument (if your processor is up to the task). With DP's multiple-track scheme, you simply instantiate a multitimbral synth and assign the desired patch or patches to successive tracks and MIDI channels. In Logic, for instance, you assign a Multitimbral Audio instrument to a track, and set the track's MIDI input to All. You can then assign the patch or patches for each MIDI channel on the synth's multitimbral setup. If you want to send your guitar's MIDI output to different virtual synths, assign the MIDI inputs of individual tracks to each string's designated MIDI channel; you can then use Logic's arpeggiators, transposition, and other MIDI processors for individual strings (for more information about string transposition, see the sidebar “Tuner Casserole”).

To further minimize glitching, it's often best to limit multitimbral synths to monophonic performance for each string and channel. That way, the synth is limited in note choices. As an additional benefit, the instrument is more effective for playing clear solo lines, because with a single-note priority for each string, each successive note on the same string will stop the previous note, just like a guitar. Consequently, you will avoid the tails of long envelopes bleeding into your next note when playing on the same string. Most multitimbral soft synths provide easy access to voice-allocation parameters in order to conserve CPU cycles, and you can usually save your setup as a multitimbral patch (see Fig. 4).

Cleanup on Track Three

Glitches recorded in sequencer tracks can pose a different set of problems. If you're recording tracks with a software synth, unwanted notes can eat up available polyphony when you most need to conserve processor overhead. If you decide to change patches, the unwanted notes could become audible again or create other playback problems. Fortunately, most modern-day sequencers offer a terrific set of tools to remove musical blemishes. For example, Sonar offers a Deglitch function that's set up to surgically remove any data you don't want to keep (see Fig. 5), and Digital Performer's Split Notes command permits the use of similar criteria for removing unwanted notes. It takes a bit of practice to figure out what doesn't belong, but I can completely clean up an entire performance in seconds with either of those programs. In DP, using an event resolution of 480 ticks to a quarter note, I can select all notes with a duration of less than 50 ticks for removal and be done with it. Likewise, you can set a range of Velocities, and the programs will dutifully remove anything less than your minimum amount. Either method works well, but I prefer to cull notes by duration, because I may accidentally play an intended note too softly.

FIG. 4: Here is a multitimbral patch I created in Native Instruments Kontakt 2. Each part uses the same bass patch assigned to one of the six MIDI channels of the guitar, and each part is restricted to single-note polyphony. In addition to conserving CPU cycles, this setup helps the samples perform like a real bass, with successive notes on the same string cutting the previous note short.

Having established several ways to clean up and fix your playing before, during, and after the fact, let me remind you that MIDI can easily become a playground for the obsessive-compulsive, and too much cleanup and precision can result in sterile tracks. A tiny amount of unevenness and glitching is a very human thing. That is especially obvious (and a bit ironic) if you need to deliver sequenced guitar parts. I'll wager that if you listen to any of your favorite guitar hero's tracks in isolation, you'll find plenty of sonic warts. For that reason, leaving that ghosted note you accidentally brushed while changing chord positions can actually contribute to the realism in the track.

Sure, the sequencer will let you set uniform durations for all the notes you played; however, one of the beauties of playing guitar is that each vibrating string has an independent life span, and some strings will naturally fade to silence sooner than others. Even if you are not trying to capture a realistic performance from your MIDI guitar, unrelenting uniformity can be exhausting to the ear.

Extra Hands

FIG. 5: Cakewalk Sonar 5.2’s Deglitch feature is specifically tailored to remove spurious notes from MIDI guitar tracks.

Some MIDI guitar controllers, such as Terratec's Axon AX 100 mkII, provide a wealth of built-in modulation controls that are ideal for animating virtual synthesizers. Software synthesizers make modulation especially easy with MIDI Learn features and automation capabilities that practically invite complex sonic motion. The Axon's modulation sources include fretboard position, picking distance between bridge and neck position, the Pickup Control Wheel, two footswitches, and two expression pedals. Roland's GR-20 and Yamaha's G50 are also viable contenders. However, if your MIDI guitar controller is a bit underimplemented in the controller department, you have other options.

One truly terrific aspect of synthesis that stems from its early days is the concept of modularity — linking components that shape the instrument's expressive capabilities. In that sense, your MIDI sequencer can become a powerful component of a synthesizer system without recording a single note. As I mentioned earlier, you can use your synth's real-time MIDI processing for a great number of tricks. In addition, you can record lots of other types of MIDI data and use your sequencer as an adjunct LFO, envelope generator, or some other modulation tool for live performance. Record whatever CC messages you need into your sequencer tracks, and just let your sequencer play them back during your performance. You can either create tempo-synced effects or, for less predictability, ignore the tempo completely and just let the sequencer run free as you play. Most modern sequencers offer lanes to edit and “paint” virtually any number of MIDI messages.

Using a guitar to play synthesizers has always been and may always be a more complicated craft than using keyboards. At last, however, with greatly improved tracking and response time, the rewards easily outweigh the effort. There has never been a better time to play MIDI guitar.

Marty Cutler coauthored MIDI for Guitarists (Music Sales) with guitarist and friend Bob Ward in 1988. MIDI guitar has come a long way since then.

STAY ON TRACK

Apart from playing technique, other factors govern your MIDI guitar rig's performance. Here's a short list to ensure that your guitar will track as accurately as possible. First and foremost: use a well-maintained guitar with true intonation and good frets. Avoid extremely low string action and extremely light strings. Keep your guitar in tune and change strings often; it's not easy for a MIDI converter to judge pitch correctly if your string is a few cents sharp or flat. Likewise, if dirt, grit, and wear are warping the shape of your strings, they just won't track properly. And when it comes to tracking, magnetic hexaphonic add-on pickups are very good, but guitars with built-in piezoelectric pickups have the edge. Crosstalk between pickup poles and adjusting and readjusting pickup height are no longer issues, and you just can't track any better than with strings sitting smack-dab on the pickup. Check out instruments from Brian Moore and Godin Guitars. If you want to add a piezoelectric system to an existing guitar, check out GraphTech and RMC Pickups.

Your MIDI converter's sensitivity settings can also help. For example, Terratec's Axon AX 100 mkII lets you set a global threshold so that lightly excited strings will not send MIDI notes. A relatively quick-and-dirty remedy for unintended MIDI data is to tweak your synthesizer's Velocity curve so that notes resulting from false triggers are inaudible. Generally speaking, glitches have lower Velocities than the notes you intentionally play, so setting a curve that requires a high-Velocity threshold to produce sound will suppress glitch notes.

TUNER CASSEROLE

Ever since the demise of Roland's GM-70, the ability to store customizable MIDI tunings has been missing from guitar-to-MIDI converters (with the exception of Yamaha's G10, which used a proprietary controller instead of a real guitar). With version 5.26 of the Terratec Axon's firmware, customizable tunings have returned, topping a list of improvements (as of this writing, the current firmware is 5.42). The Axon's editing software offers a drop-down list of alternate tunings you can load and store in a preset, and you can add your own custom tunings to the list.

FIG. A: Phi Software Open Tuning 1.5.1 lets you transpose the MIDI output of individual MIDI guitar channels and perform a variety of MIDI mapping tricks.

For controllers without open-tuning capabilities, Mac OS X users can download Phi Software Open Tuning 1.5.1 (see Fig. A). As with the Axon, you can choose from a long list of presets or customize and store your own. You can easily map any MIDI guitar's individual string output to play standalone soft synths directly or synths loaded into sequencers with Apple's IAC bus. If you want to use your controller on a single MIDI channel, you can create tunings by assigning MIDI Note Numbers to transposition zones; that offers intriguing possibilities for other single-channel controllers such as keyboards and wind controllers. You can download a free trial copy or purchase a full working copy for $29 at www.open-tuning.com.

You have at least two ways to achieve alternate tunings in your sequencer software. As long as your guitar controller is transmitting on an individual-string-per-channel basis, you can map notes to a new note. MOTU Digital Performer — because of its channel-per-track setup — does this easily. Some tinkering with the MIDI-mapping features of other sequencers (such as Apple Logic's Environments window) can provide the same result. Naturally, most multitimbral soft synths provide a transposing capability for each part, so you can create alternate tunings if your sequencer doesn't offer real-time transposition.