Six-String Synthesis - EMusician

Six-String Synthesis

MIDI guitar might conjure up the image of a guitarist wailing away as a synthesizer obediently translates every nuance of picking, scraping, and bending
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MIDI guitar might conjure up the image of a guitarist wailing away as a synthesizer obediently translates every nuance of picking, scraping, and bending into astounding synth leads or profoundly realistic orchestral masterpieces. Unfortunately, dreams quickly turn to disappointment if you don't understand how guitars, MIDI converters, and keyboards interact. That understanding is crucial to experiencing the full potential of MIDI guitar systems.

It's a popular myth that poor tracking and data-conversion delays are the primary reasons guitarists can't attain MIDI nirvana. Although MIDI guitar systems are much better than they used to be, the guitar-to-MIDI connection still has technical limitations. Even if MIDI guitars could instantaneously track every gesture, you'd still have to deal with the way devices transmit and respond to MIDI.

Many guitarists have exaggerated expectations of what MIDI guitar converters can do; at the same time, they underestimate the tremendous power and flexibility of synthesizers and samplers. In this article, I'll examine the relationship between MIDI guitar and synths and samplers (see the sidebar “Guitar à la Mode” for information about the modes that determine how synths respond to MIDI messages).

TAKE NOTES

Many performance techniques used by guitarists are lost in the translation to MIDI. When you play a keyboard, it initially conveys pitch and whatever results from the keystroke's Velocity — typically, volume and brightness.

On a MIDI keyboard, press a key very fast and then very slow, and notice the difference in the sound. What you hear is the only difference you can make when you play a note on a MIDI guitar. You can't palm-mute a keyboard or pick it at an angle as you can a guitar, and you certainly won't hear any effect if you strike the keys with your nails or finger pads.

Real-time MIDI performance is analogous to telling a story by writing it instead of using your voice. You cannot employ your favorite vocal tricks such as inflection, whispers, or shouts to get your point across; you need to focus on tools such as word choice and punctuation. To extend the analogy, the exact meaning of the story is also subject to interpretation on the receiving end. Depending on a receiving device's MIDI implementation, it can reinterpret, misinterpret, or ignore certain parts of the message.

AROUND THE BEND

As one of the most important control parameters, Pitch Bend can enhance or ruin your MIDI guitar experience. Pitch Bend commands tell a synth or sampler whether to bend pitch sharp or flat, but not always how far to bend it; the precise interval depends on the receiving instrument's range settings. Most of the time, you should set your MIDI sound source's Pitch Bend depth to the greatest interval you normally bend your strings and then add one more half step.

To avoid disaster, make sure your guitar-to-MIDI converter's Pitch Bend range matches your synth or sampler's Pitch Bend range. Most synth programs default to a range of two half steps, so you'll probably need to change them. Some synths let you change the range globally so that with one parameter tweak, you can match the maximum Pitch Bend range to that of your MIDI guitar converter. Some MIDI guitar converters are able to transmit Pitch Bend Change messages (CC 6, CC 38) that automatically set up the receiving synth with a matching Pitch Bend range. With other synths, you should resign yourself to setting each patch's Pitch Bend range individually.

Picked or plucked guitar strings start slightly sharp and then settle into a stable pitch over time, which can adversely affect your sound source's pitch by creating Pitch Bend data. Keep in mind that some keyboard instruments, including pianos and organs, cannot bend notes, and pitch bending can sound unnatural. Although you may hate to give up one of your guitar's natural emotive tools, consider eliminating Pitch Bend information altogether for those instruments. Still, if you feel particularly adventurous, you may want to bend notes on pianos and organs anyway.

You can filter out Pitch Bend messages at several locations in the MIDI stream. Because MIDI guitars can generate a constant stream of Pitch Bend data, disabling Pitch Bend in your guitar-to-MIDI converter delivers the best results. If your MIDI converter doesn't allow you to store a Pitch Bend range for each program, you can program your synthesizer patches to ignore Pitch Bend messages by setting their ranges to zero.

DIGITAL DEXTERITY

MIDI guitar controllers let you create vibrato manually; when you wiggle a string, the controller transmits Pitch Bend messages that translate to vibrato. Keyboard players rarely produce vibrato with their pitch-bend wheels, though; it's just too hard to do gracefully. Instead, they use modulation wheels to create low-frequency-oscillator (LFO)-induced vibrato. Sending Modulation messages to impart vibrato might seem like a weak substitute at first. However, you can smoothly change vibrato depth and speed, and a synthesizer's vibrato goes above and below the original pitch as it does with most instruments.

If you're trying to sound like a keyboard player, vibrato is usually produced with Modulation messages, but they're not the only way to add vibrato. You can control an LFO with an expression pedal or a breath controller. You can even map Pitch Bend messages to change vibrato depth so that as you bend a string farther, the vibrato gets deeper and faster.

Given that your hands are busy most of the time, any modulation effects that you can automate are a godsend. The easiest type of automation is programming your synth patch to create vibrato with a free-running LFO that fades in after you've held the note for a certain length of time.

SWEET RELEASE

Most MIDI guitar systems can easily take advantage of other MIDI Control Change (CC) messages. One immediately useful device is the sustain pedal. If your MIDI converter has a footswitch input, you can connect a sustain pedal or another momentary footswitch. Most MIDI guitar systems offer built-in pedals or input jacks for pedals that can perform sustain, hold, or other functions.

Synthesizers usually respond automatically to Sustain Pedal messages (CC 64). Such messages are great for adding a natural release to acoustic- and electric-piano sounds, for example. For indefinitely sustaining sounds, a Sustain Pedal message can hold any notes that are playing until you release the pedal. If you're careful not to overuse it, a sustain pedal can give your synth a life apart from your guitar's sound.

Even if your guitar lacks a footswitch input — as do the Parker MidiFly, Godin guitars, and Brian Moore guitars — you can still incorporate footswitches (see the sidebar “Instrument-Specific Tricks”). Most MIDI keyboards offer footswitch and expression pedal jacks, and you can automatically merge their inputs with your guitar's MIDI data. MIDI-mapping devices can turn a footswitch into the MIDI message of your choosing.

Another useful controller message is Sostenuto (CC 66). If you step on a pedal that's sending Sostenuto, the synth will continue to hold the notes that you're playing, but unlike Sustain, any notes played afterward will not be held. That means, for example, that you can hold a pad and then solo over it; you can even play a different sound.

Sostenuto is available with several variations on many MIDI guitar systems, including Blue Chip Axon and Roland units. For instance, the Roland GR-33 provides looped drum and percussion grooves; hitting the pedal lets you sustain the loop while you solo with a different patch.

Expression pedals and breath controllers are some of the best tools for taking advantage of a synthesizer's expressive capabilities. Analog synthesizers are famous for huge, beautiful filter sweeps. Use CC messages or delayed envelopes to sweep resonant synthesizer filters. Assign Pitch Bend to change your synth filter's cutoff frequency. Bending notes and simultaneously sweeping the filter is a potent and expressive trick, and adding a delay effect with regeneration will enhance the sweeps.

Filter sweeping isn't the only trick for creating animated timbres; try mapping Pitch Bend to control pulse-width modulation, for example. Most contemporary synthesizers support CC messages in ways that can drastically alter your synthesizer's sound. Consult the MIDI-implementation chart in your synth manual to discover a wealth of possibilities.

SENSITIVITY SESSION

Adjusting your MIDI guitar controller's sensitivity is crucial to good communication between your guitar and your synth. Ideally, each string should register a range of picking dynamics from your softest strokes to your hardest strums with a continuously increasing value.

To that end, most MIDI guitar controllers offer some form of level meter to provide a visual aid when you adjust string sensitivity. Attempt to set your MIDI converter's sensitivity so that a consistent level of soft plucking triggers each string, and then ensure that the peaks match each other when you play harder so that they just barely hit the highest Velocity. That should result in a uniform Velocity response from each string.

Even with the sensitivity calibrated, it is possible for MIDI Velocities to jump unexpectedly to a high or low value. If that occurs, adjust your synth in order to reduce its amplitude and filter responses to Velocity. That will give your synth performance a more cohesive feel, but be careful not to completely squash the dynamic range.

REACH OUT AND TOUCH

As a guitarist, you are intimately familiar with the feel of the strings as you play them and the close relationship between your touch and the amplified guitar sound. Unless your amp volume is very high, you can also hear the vibration of the strings. Your brain uses that sensory information even before the sound travels from the speaker to your ear.

With a MIDI guitar, however, that tactile feedback is minimal or even nonexistent at first. To compensate, wear headphones or place the monitor speaker as close to your ears as possible to make it easier to ignore the physical guitar sounds. On a patch-by-patch basis, you will eventually develop a more intimate sense of touch with your MIDI guitar, and the experience will feel more tactile.

Emulating the performance styles of other instruments in terms of their note ranges and typical phrasing is an important aspect of playing synthesizers and samplers. Those elements are often more important than the degree to which the timbre accurately matches the real thing, and common guitar techniques can often run counter to an emulative performance.

For example, when reproducing piano, organ, or ensemble performances, strumming is rarely a desired effect. You should become proficient at plucking all of the strings simultaneously. Although MIDI allows you to go beyond the capabilities of any instrument's acoustic counterpart, let your ears and sense of taste be your guide.

THE OUTSIDE PITCH

By nature, most pitch-to-MIDI converters create a lag in the output of MIDI data generated from lower-pitched strings. Almost any synthesizer will transpose pitch an octave or two, however; you can usually transpose your synth's pitch globally or change oscillator frequencies at the patch level. Transposing lets you use your MIDI guitar's higher strings to play lower pitches on your synth — the higher the guitar note, the faster the MIDI converter can recognize the pitch. Playing an acoustic-bass patch from a different position on the fingerboard might take some getting used to, but tracking accuracy will definitely improve. If your MIDI converter can transpose notes, you can try this technique without having to do any synth programming.

In earlier times, some guitar controllers offered the ability to tune the output of individual strings to any pitch, allowing alternate tunings such as DADGAD or CGCGCE. Lamentably, because that feature costs more to implement and complicates the user interface, manufacturers have stopped providing it; few, if any, current MIDI guitar systems permit you to transpose individual strings by semitones. Fortunately, you can find a number of work-arounds for that shortcoming.

Any decently implemented multitimbral synth will transpose individual patches in semitones as well as allow each patch a distinct MIDI channel. After you have matched the sound source's MIDI channels to your guitar controller's string output, simply transpose each patch to taste. By programming and storing a different tuning in each multitimbral location, Program Change messages allow you to change your MIDI guitar's tuning without touching a single tuner.

If you transpose each string's MIDI output by octaves, you can create incredible chord voicings. Your guitar's six notes can be widely scattered over several octaves or bunched together into the same octave, allowing you to play cluster chords that were once the exclusive domain of keyboard players.

GET OUT THE MAP

Because samplers can remap notes, they can transpose every note from your controller to play any note you choose. That means that you can find comfortable fretting and picking patterns and then choose the pitches or sounds that result from each fret your fingers play.

For example, suppose that strumming the six open strings of your MIDI guitar sends the following notes: low E (MIDI Note Number 40), A (Note 45), D (Note 50), G (Note 55), B (Note 59), and high E (Note 64). You could assign samples in your sampler's keymap so that strumming, brushing, or picking across the strings produces a melody or riff. Although remapping notes is time-consuming, you can devise amazing parts that you control in real time.

Furthermore, most MIDI sequencing software allows you to transpose incoming MIDI data in real time, either by MIDI channel or by track. In Mark of the Unicorn Digital Performer, for example, you can specify each track's transposition value. You have to set up an individual input, track, and MIDI-channel output for each string. Be certain to save your setup as a template; once you've done that, you can quickly create a variety of alternate tunings at any time.

It's also simple to assign different sounds or different synths to any string (see Fig. 1). Even if you don't perform with sequenced tracks, a sequencer's potent real-time MIDI-processing capabilities make a strong case for taking your computer to a gig.

Whatever method you use to transpose your MIDI guitar's output, you'll probably want to minimize the acoustic and amplified output of the strings. Alternatively, you can create interesting harmonization effects by blending the sound of your guitar with the synth transposed to a unique interval.

ENVELOPING CONCERNS

Longer attack and release times can create musically useful atmospheric effects. The majority of synthesizer players are comfortable with the fact that some patches develop slowly when you press down the keys. Other patches start more quickly but continue to sound long after you release the keys. As a MIDI guitarist, you should learn to continue playing even if you don't hear your synthesizer the moment you pick a string.

With a little programming, you can make slow envelopes work for you in dramatic ways. Try creating a two-layered synthesizer sound with a bright, sparkling sound on one layer and a fuller sound on the other. Program a longer release time for the bright layer and a shorter release for the fuller layer. The fuller sound will fade away and leave the bright, sparkling sound to linger, thus avoiding sonic mud (see Fig. 2).

Some synthesizers have envelope generators that tack on a delay before the attack stage, delaying the time between a MIDI Note On and the sound's onset. By using subtle amounts of delay time (from 20 to 80 ms, perhaps), you can achieve a doubling effect between your real guitar sound and the synth. If you create multiple layers, each with a longer initial delay time (50, 100, 150, and 200 ms, for example), you'll get a very musical echo effect. Changing the waveform for each delayed layer will result in rhythmic echoes with a different timbre for each layer (see Fig. 3).

POWER GLIDE

Portamento imparts a wonderful gliding effect to your synthesizer sounds. It's even more dramatic if you combine a synthesizer sound that has portamento with the output of your guitar; the guitar will hit a note dead-on while your synthesizer swoops into the pitch. Another benefit of portamento is that it can help smooth over possible glitches. Experiment with various types and amounts of portamento in your synth sounds.

It might take some getting used to, but playing a monophonic synthesizer patch that uses portamento is an enjoyable way to learn new expressive techniques. Brushing your pick across all six strings from low to high or vice versa, for example, causes the synthesizer to create wide pitch sweeps. You can also create an effect similar to Eddie Van Halen's powerful combination of hammer-ons and fret tapping by picking a string and then hammering on the same string or another one. Include a subtle amount of portamento to make the note transitions as smooth as possible. Because you can tap any string at any fret, the technique takes on added dimension and range. In order to get the full effect of a monophonic synthesizer, assign your controller to a single MIDI channel.

CONTROL FREAK

Why not let your MIDI guitar control other devices besides your synths? Program Change can radically alter your MIDI-instrument setup with the push of a button, but a Program Change sent to your synth won't necessarily select a musically meaningful patch on your effects processor.

Fortunately, most MIDI effects processors offer patch-mapping features that convert one Program Change into another. You can remap patches so that if you send Program Change No. 32 from your MIDI guitar to call up an eerie atmosphere on your synth, for example, your effects processor could call up Program Change No. 73, a complementary echo effect. With just one Program Change, your synths, guitar rig, and vocal processors can all jump to a new, custom-tailored sonic scene.

Some synthesizers can process external audio signals. Try routing vocals to your synthesizer and then modulate the filter cutoff with your MIDI guitar. Some synths can even modulate an incoming analog signal's pitch so that your voice will follow notes you play on your MIDI guitar.

Many synthesizers have built-in sequencers, pattern players, or arpeggiators that start when you play a specific note. If you set the trigger note above the normal range of the guitar, you can send a Start message by playing a harmonic. That lets you start your sequence or arpeggiator at will and still play the full range of your guitar.

A BEAUTIFUL RELATIONSHIP

I hope that this article has provided you with an improved understanding of the relationship between your MIDI guitar and your synthesizers. Once the kinks are worked out, an entirely new sonic universe is yours to explore — and it's one that can't be visited by someone who plays only guitars or keyboards.

Daniel Fisheris an associate professor of music synthesis at Berklee College. He plays keyboards and backup guitar and sings with the tribute band Pink Voyd (www.pinkvoyd.com).

GUITAR À LA MODE

Perhaps the most distinguishing feature of MIDI guitar controllers is their ability to send a different stream of MIDI data from each string. Understanding that capability is crucial to a healthy relationship between your guitar and your synthesizers. The MIDI protocol conveniently offers four modes that determine how synthesizers respond to incoming MIDI messages. A MIDI guitar can transmit over a single MIDI channel or six channels at a time; synthesizers respond in one of the four modes.

MIDI Mode 1

In Omni On, Poly, your synth responds to MIDI data without regard to the originating MIDI channel. MIDI Mode 1 is a remnant of the early days of MIDI, when the major concern was simply controlling one synthesizer with another. Few modern MIDI devices implement Mode 1. As it pertains to MIDI guitar, the mode will work as long as your controller is set to address a single synthesizer with Pitch Bend disabled. If you are integrating your MIDI guitar and synthesizer into a sequencing system, avoid this mode.

MIDI Mode 2

In Omni On, Mono, your synthesizer can play just one note at a time, and it responds to incoming data without regard to MIDI channel. Again, this mode is best avoided in a sequencing system or when you have multiple MIDI devices.

MIDI Mode 3

Omni Off, Poly is the most commonly used of the four MIDI modes. Your synthesizer responds only to MIDI data on selected channels, and it can play more than one note at a time. Mode 3 is great for using your MIDI guitar with a sequencer because you can play chords.

MIDI Mode 4

Omni Off, Mono is the performing MIDI guitarist's mode of choice. Your synth responds selectively to individual MIDI channels and plays one note at a time from each channel, and your guitar can play one note per string. Monophonic performance minimizes the audible effects of glitching and prevents notes with long decays from interfering with subsequent notes played on the same string and MIDI channel. Mode 4 also works well for sequencing guitarlike performances with separate Pitch Bend from each string.

INSTRUMENT-SPECIFIC TRICKS

The Parker MidiFly and Brian Moore MIDI guitars can switch between three modes: Single-MIDI-Channel mode without Pitch Bend, Single-MIDI-Channel mode with Pitch Bend, and Multichannel-MIDI-mode with Pitch Bend.

The first mode lets you disable Pitch Bend at the source with the flip of a switch, which is handy for emulating pianos or organs. The second mode allows Pitch Bend as long as you're playing a monophonic line. If you play a second note, Pitch Bend is disabled; that's good, because sending Pitch Bend from more than one string over a single MIDI channel causes ugly, out-of-tune confusion from your synthesizer. Multichannel mode assigns a separate MIDI channel to each string.

The MidiFly provides a MIDI In jack that can merge MIDI signals from another controller with those generated by your guitar. That lets you add a MIDI foot controller, breath controller, or MIDI Program Change device.

Axon Tricks

One of the most fascinating features of the Blue Chip Axon MIDI converters is their ability to sense a pick's position between the bridge and the neck and send that data as a parameter value. The Axon manual makes several suggestions about where you might assign the data — including the mod wheel, filter cutoff, or pan — but you could use it in many ways. For example, you could send a Control Change (CC) message that changes a rackmounted signal processor's effects depth. Try anything and everything you can imagine, and you might discover some worthwhile results.

Yamaha G50

The Yamaha G50 has several features in common with Axon MIDI guitar converters. One unique trick is its Touch Control feature, which has the ability to send any CC message you choose, based on the force of your picking. Try assigning Touch Control to the filter's cutoff frequency and crank up the resonance a bit to give your synth an envelope-follower effect.

Although the Axon and Yamaha units send CC messages by pick position, they send a discrete value for each note you play. Some CC messages are meant to be continuous (Modulation Wheel, for example) and do not fare well as discrete messages. However, both controllers let you set upper and lower modulation values, enabling a more subtle modulation effect. Better yet, the Axon provides two programmable expression pedal jacks that you can use for continuous forms of modulation. For the Yamaha G50, factor in an extra $350 for the optional MFC10 foot controller.