The most interesting part of playing an electric violin, in my opinion, is twisting the sound with electronic effects (if you aren't twisting the sound, why play electric?). Effects units come in a variety of shapes and sizes, some of which produce subtle changes in the sound, some of which transform the instrument entirely.
Effects are being used with a wide variety of instruments these days, but most effects units were originally designed for electric guitar. Effects are sold separately as single pedals (generally an aluminum box 2"H x 2"W x 4"D or so), or as multi-effect units in a pedalboard (usually a plastic wedge 1"H x 18"W x 6"D box with a half-dozen pedals on it) , compact interface (some can be clipped to your belt), or rack-mount unit (a box 2"H x 19"W x 6-10"D or so, with screw holes that let you mount it in a rack). Which form you buy your effects in depends both on budget and use. Multi-effect rack units are typically more expensive (the best effects are available only as rack units), and can be more problematic during live performance. Pedals are generally the cheapest route, and the most reliable on the road.
If you're performing and want a solid unit that won't break and that you can easily troubleshoot if things start going wrong, get pedals. If one goes bad, pull it out of the chain and continue playing, albeit with less texture to your sound. (If a rack unit goes belly up or just gets generally cranky, you can't unplug the offending effect module...you're stuck until you get the entire unit happy again.)
If you're recording, however, a rack unit is a must. (The Digitech Studio Tube preamp is shown here.) A rack unit is where you'll find the best quality and the most flexibility, and will ultimately be a better investment if you plan on recording for CD. Many rack units offer combinations of virtually all effects available, and some even include tube preamp sections for that really "brown" distorted sound. (For details on amplifiers and distortion, see the Performance article.)
Also note that not all effects are electronic. Many folks will play with different room/microphone/instrument combinations to produce the texture they want. And in some cases, these solutions may be more effective than an electronic substitute. Experiment. It's good for you.
A note about the sound clips: I created each clip on a Jensen 5-string violin, playing through an ADA MP-1 tube preamp. The reverb, delay, and flange sounds were created with BOSS (Roland) reverb/delay and flange pedals; the wah sound was created with a Dunlop CryBaby; the distorted sound was created through a distortion channel on the MP-1. Some of the clips have a wee bit of reverb in addition to the effect in question sos they sound a bit better. I'll add more clips as time goes on, so keep checking back!
Reverb - The most common and useful effect, reverb (short for reverberation) allows you to control the perceived size of the room in which you're performing. (The unit shown here is a Boss combination reverb/delay pedal.) You can sound like you're playing in a closet, a small performance hall, or in a deep cavern. Good reverb units allow you to control a variety of parameters, including the time before the first relection returns (i.e. the time from when sound leaves your instrument to the time when it has bounced off the nearest surface and returned to your instrument), the number of reflections (how long the sound bounces around the room before dying out. A large room with hard surfaces will let sound bounce longer than a small room with padded surfaces.), the "density" of the reflections (essentially accounting for the complexity of the room. More surfaces make for more complex reflections, whereas a small number of surfaces make a fairly simple reflection.), and so on.
Good reverbs are also "warm," in the sense that the nuance of the instrument is retained in the reflected signal. This last characteristic is most of what you're paying for in high-end units, as they have the processing horsepower to accurately reverberate all areas of the sound without loosing any fidelity. A warm, smooth reverb is kinda like really good speakers...the feeling of "being there" is greater.
Here's a sample of reverb set to a fairly large room, with lots of feedback and very little "dry" signal:
(AIFF file, 8 bit, 11 kHz mono - 201 K)
(WAV file, 8 bit, 11 kHz mono - 201 K)
Delay - Where reverb provides a reflection of the sound that's dependent on the characteristics of the virtual "room," delay creates a second signal based on a preset time. Delay can be set quite short (in which case it sounds kinda like a cold reverb), or quite long (where the delayed signal comes in several seconds after the original notes are played). Jeff Sick makes extensive use of delay as accompaniment on his album "Street of Dreams," and Drew Tretick uses delay on his Zeta demo video to play canons.
All delay units allow you to specify the time before the note is repeated. Many also let you specify the number of times the note is repeated, the rate at which the volume of repeated notes decays, and in more advanced units the stereo channel in which the notes are repeated.
Here's a sample of delay with a relatively short time before the repeat, and a little bit of reverb:
(AIFF file, 8 bit, 11 kHz mono - 187 K)
(WAV file, 8 bit, 11 kHz mono - 188 K)
Pitch-shifting - Pitch-shifting takes a variety of forms. The most common uses are in chorusing, flanging, or rotary-speaker effects, described below, in fixed-interval effects, and in adaptive "harmonizers." In fixed-interval effects (most commonly found as octave or double-octave pedals) the main signal is reproduced simultaneously one octave lower. Some newer pedals allow you to select a variety of intervals for the second pitch.
When using a harmonizer, you tell the unit what key you're playing in, and it produces additional harmony parts from the note you play. (The Digitech Vocalist harmonizer, which can produce full 5-part harmony, is shown here.) This can be used for self-accompaniment, but is more commonly used when soloing to produce a highly complex sound without altering the original sound of the instrument.
Here's are two samples of pitch-shifting. In the first, the source tone is duplicated at intervals of a fifth and a ninth above. In the second, the source tone is duplicated an octave below (this is how your typical Octaver pedal will sound):
Dissonant shift (.AIFF file, 116 K)
Octaver (.AIFF file, 116 K)
Chorus - A common effect for guitarists, chorusing makes a copy of the main signal, and plays back the copy with a very slight delay (10-25ms or so) and pitch shift (not so dramatic as to sound out of tune, but enough to sound like the inherent tuning differences between two instruments playing the same note at the same time). The name comes from the effect of making one instrument sound like a "choir" of instruments playing the same note at the same time. This makes the instrument sound "fatter" and more complex. It also produces a smooth, blurred sound that can "warm up" an otherwise sterile sound. Chorusing effects units typically let you control the intensity of the effect, the speed with which the pitch is modulated, and the depth of modulation.
Here's a sample of chorusing. The first figure is "dry," and the second is chorused:
(.AIFF file, 132 K)
Flanging - A sibling of chorusing, flanging also works by delaying a copy of the main signal. Flanging, however, delays the copy in a much shorter span of time (1-12ms) than chorusing. This makes for a more nasal or metallic sound, or with some settings the effect of a jet airplane flying overhead. Most flanging units also allow you to specify "resonance," in which a certain percentage of the flanged signal is fed back to the processor. In some cases you can twiddle the knobs on a flanger to very nearly get a chorused sound, albeit without all the warmth of a chorus processor.
Here's a sample of flanging, with the resonance and depth cranked up:
(AIFF file, 8 bit, 11 kHz mono - 105 K)
(WAV file, 8 bit, 11 kHz mono - 105 K)
"Leslie"/Rotating speaker - The rotating speaker was originally developed in the 60's by Don Leslie. The speaker cone was mounted on a mechanical platform that was rotated in a circle, providing a pulsing sound based on both the changes in volume as the speaker rotated, and the doppler effect (albeit small) created by the rotation.
Wah-wah - Masterfully used by Jimi Hendrix, the "wah" pedal lives up to its name: as the pedal is rocked back and forth, the note being processed makes the sound of someone saying "wah." Most useful in blues and funk settings because of its speechlike expressiveness, and can also find a home as a kind of limited resonance filter (slowly making the sound more, then less nasal).
Here's a sample of wah-wah:
(AIFF file, 8 bit, 11 kHz mono - 132 K)
(WAV file, 8 bit, 11 kHz mono - 132 K)
Distortion/Overdrive - Distortion occurs when an audio circuit is driven beyond is designed tolerances. Well, actually a whole bunch of things can occur to cause distortion, but the end result is a "crunchy" sound. Distortion can be controlled to make a sound thicker and "chewier" (kinda like a Zinfandel, I suppose). Some distortions are used sparingly to make a sound complex (as in blues), others (as in heavy metal) are used to make the sound as intense as possible.
Really good distortion, heavy or light, is generally referred to as "brown," because it gives the sound a smooth "dirty" texture, and is complex. Poor distortions tend to be less complex, with a more strident and abrasive texture (good and bad being relative, of course, depending on what you want to use it for). Really brown distortions can only be had via tube amplifiers. Although solid-state circuits (like the chips found in computers) can approximate a controlled distortion, the physical properties of vacuum tube transistors make their sound particularly smooth, warm, and complex. The down side of tube amplifiers is that tubes deteriorate and break, whereas solid-state circuits pretty much don't. I also gather that tube amps are more expensive to build, since they typically cost more, but this might just be marketing.... See the Performance section for more discussion of amplifiers.
Here's a sample of tube distortion:
(AIFF file, 8 bit, 11 kHz mono - 152 K)
(WAV file, 8 bit, 11 kHz mono - 152 K)
Equalization - An equalizer in the purest sense simply makes all sounds equally strong throughout the frequency spectrum. 'Course in reality this isn't what you want, and most equalization (or "eq'ing") is done to shape the sound to fit a particular use. EQ can be particularly important when playing or recording in an ensemble, where certain frequency ranges of each instrument are important, and others "step on," or interfere with, other instruments.
Compression/Limiting - This effect is primarily used to prevent a signal from getting out of hand in an ensemble setting, or on a recording where an overly "hot," or intense, signal can cause distortion on the tape. (An Alesis rackmount compressor is shown here.) Compression is also used, however, to give added "sustain" to guitars, which, because plucked, can't produce a long sustained note without additional plucking of the string.
Here's a sample of a fairly distorted signal both with and without compression. Note the dynamic range of the "dry" version, where I go from soft to loud, and the lack thereof in the compressed version:
(.AIFF file, 396 K)
Digital synthesis/transformation and MIDI control - There are two effects on the market that can take a violin (or guitar) sound entirely away from the realm of traditional analog effects: digital synthesis or transformation, or MIDI control.
In digital synthesis, the signal from the instrument is used only for its "controller" aspects. That is, pitch, velocity, pressure, and so on are important, but timbre (the actual tone or "texture" of the instrument's sound) is discarded. The synthesizer uses the controller data to trigger sounds in its memory, which are typically digital sound samples of other instruments. This kind of synthesizer does not convert the controller information to a MIDI signal, and as such can't control an external synthesizer or keyboard.
Roland makes the most popular guitar synths (the GR-09 is shown here), but also makes a "Virtual Guitar" synth. This device manipulates the original sound, including its timbre, just as a standard effects unit does. But in this case, the original sound is altered via a physical model of a guitar. I won't go into the details of "physical modeling synthesis" here, but suffice to say it's a significantly different method than that used by traditional effects processors, and produces a number of timbres and sounds that no other processor can produce.
Both Roland and Zeta make "pitch-to-MIDI" converters. These processors convert the controller information (pitch, velocity, pressure, and so on) into a MIDI signal which can then control an external synthesizer. These converters have no sound-producing capabilites on their own, and serve only to translate the instrument signal to a MIDI signal.
That's a basic introduction. If you want more detail, I can recommend a number of books that discuss all this more completely.