While I was covering the main families of effects that are being used in electric guitar's world, I wasn't talking about more arcane effects, maybe not just developed with guitar in mind but used for some one in some song.
Theremin is an instrument itself. The theremin has two antennas, first antenna controls the volume of the signal while the second one controls the pitch. It was designed to be played as an instrument itself so, one hand should be moved near the tone antenna to select the notes while the other hand should give the right volume level to each note, being moved around the second antenna.
As you can imagine, to control an instrument of that kind isn't easy and, even that there are some Theremin virtuosos around the world, is not a wide spread instrument.
First time I've heard the Theremin was in "Whole lotta love" by Led Zeppelin. Those incredible sounding howlings (with hard echo repeat) were really amazing. Nowadays, I can see Joe Bonnamassa using it (very well) in "I've got Paid" but, I see very few people dealing with such an effect and, I think its mainly because: it's damn expensive to have a good theremin, it's very difficult to imagine where its sound can suit one of your songs, needs a dedicated amp (and probably a dedicated effects chain, at least one delay).
If you are curious about this effect, watch this video of "Whole Lotta Love" played live. Not the version that I like more but, that Theremin can be clearly heard around minute 2:45.
But you will probably love more the more uptodated sound of this incredible song performed live by Joe Bonammassa. The first Theremin hawling can be heard around minute 4:36. When used just to accentuate some specific (and short) parts, wisely, it's an outstanding effect that I love.
I would like to see some kind of Talkbox-Wah-Theremin pedal that can be inserted in your chain with stereo outputs: one dry signal and one wet signal (with blend control). With the talkbox's tube we could control the Theremin pitch and, with a Wah rocket we could control the volume of that signal. That's why I call it talkbox-wah-theremin. Hey pedal makers! I am callenging you to build something like this! and, please, send me one for free in pay back for the idea!. LOL.
What about, theremin, wah and talkbox modes in same pedal?. LOL.
I think Zachary Vox is the only one really skilled and crazy as hell to achieve an exciting box of that kind that can be of real use. Zach, come on, move your brain's machinery.
I have to stop this, right now!.
E-Bow. The ebow is some kind of device that alters the magnetc field of our pickups, making them to pick up the sound of our strings, even without actually touch them. Since this device is continously feeding that changes, we can achieve violin-like eternal sustain but, this is a very very difficult effect to use, even more difficult that to use a violin-arch to play our guitar (as Jimmy Page did in "Dazed and Confussed").
If you are curious, just watch this youtube video to understand what the ebow does. The sound is coming from your pickups but, it seems a completely different instrument, right?. Don't think that it's easy to play, in any single way. This man is a real master of such a device use.
I am quite sure I am missing some other effects but, in the case of these ones described above, they cannot be considered Pedal Effects, because they cannot be chained on a pedal board and, most of those will need a separate rig (amp, effects) to be able to use them.
Kaoss Pads. The Kaoss Pad is just a Midi Controller. The sound of the guitar is being traduced into Midi Notes. The intensity, velocity among other parameters can be all them controlled with the help of a digital pad that is installed on the guitar. This works like a Pad-Mouse (those seen in many lap tops) and, depending on which area we touch and how, some midi parameters are being modified.
Of course, the ouptut of this pad is just a train of digital data that is sent to a midi instrument (maybe a synthetizer, maybe just a PC with a DAW software that has several software synths available, ....).
So, we have our real guitar signal going the typical analogic audio way and a midi digital signal that goes to whatever other midi devices.
For sure, it can be interesting for MIDI stuff but... like in the case of midi guitars, it just sounds so digital and synthetic that is just the oposite to a guitar. I recognize that can be an interesting thing to record some midi stuff with a guitar, if you don't have the skills to play a keyboard (as in my case).
As with many other weird effects, I expect that some day, someone will bring to us to interesting song using the Kaoss Pad, as we had with "Whola Lotta Love" using the Theremin.
Let the people investigate and experiencing it!.
If you are curious, take a look to this video. You can see that there is some wide field for experimentation with some device like this one:
What we usually recognize as a pedal effect is some small unit that can be switched on/off with our foot, that is stackable in our pedal chain and that, modifies (on-the-chain) the sound of our guitar. And, in this case, it doesn't really mean if the effect was designed for an organ, a trumpet, a guitar, a bass guitar or whichever other instrument, if it can work in our chain, it can be considered a guitar's pedal effect.
We will see that, to have in mind the instrument for which every effect is designed has consecuences and, one of the worst ones is the impedance match. While mics, organs, keyboards and many electronic musical devices have a very low impedance, guitars have high impedance and then, to use pedals designed for low impedance instruments in a high impedance instrument brings some drawbacks. But we will talk about this later.