Here's a a short (but good) ghost Hexpander review.
When you play a note or adjust a knob on a MIDI keyboard, it transmits MIDI data. A guitar pickup, however, produces analog electrical current that must be converted to MIDI data before it can control MIDI devices. To accomplish that conversion, a hexaphonic (literally meaning “6-voice”) pickup sends 6 discrete electrical signals (one for each string) through a 13-pin connection to an external converter unit. The converter continuously analyzes the signals' variations in frequency and translates them into MIDI data. Graph Tech has entered the MIDI guitar arena by introducing the Ghost Modular Pickup System, which features the HexpanderMIDI-ready preamp.
Ghost in the Machine
The system's most essential components are a piezo saddle pickup and a preamp module. Graph Tech manufactures a variety of saddle pickups (from $119 to $275) for Strat- and Tele-style, Tune-o-matic, and other guitar bridges, as well as Precision- and Jazz-style, Hipshot, and other bass bridges. Separate piezos in the saddle send an electrical signal from each individual string to the preamp.
You can choose from two preamp modules, the Hexpander and the Acousti-Phonic. Each is a circuit board installed in your guitar. The Hexpander preamp ($250) lets you use the Ghost system as a MIDI controller. The Hexpander routes the hexaphonic signal through a 13-pin output to a third-party MIDI converter (not included). The Hexpander comprises the preamp module, requisite wiring modules, and a 13-pin jack, and must be installed inside your guitar. The system's modularity lets you choose from many optional features such as a volume pot ($26), a program-select switch ($33), a 7-pin wiring harness to route your guitar's magnetic pickup's signal through the 13-pin output ($13), and a switch to toggle between the magnetic pickups, Hexpander system, or both ($26).
The Acousti-Phonic preamp ($100) promises to make your electric guitar sound like an acoustic, but I didn't request one to evaluate. Both preamps can be installed in your guitar at the same time.
The main complaint of musicians who use guitars as MIDI controllers is their typically poor tracking. Hexaphonic systems are notorious for tracking inaccurately, too slowly, or both. Phantom notes (triggered notes you didn't play) and double triggers (two notes when you played only one) are usually caused when a hexaphonic pickup misinterprets finger noise.
The Ghost system tackles those problems with a proprietary harmonic-dampening technology that squelches finger noise by filtering out specific frequencies for each string. Harmonic dampening reduces false triggers without sacrificing accurate tracking and results in a very clean signal. The Hexpander also incorporates a low-latency preamp design that offers far faster tracking than magnetic hexaphonic systems.
Anyone who repairs electric guitars can install the Ghost system in your existing guitar. Graph Tech's Web site has a list of qualified technicians who can perform the retrofit. I've had years of experience playing guitars with magnetic and piezo hexaphonic retrofits, and two months ago I had the Ghost Hexpander system installed in my custom-built Koll Guitars Tornado.
I used the Hexpander connected to a Roland GI-20 MIDI interface to control several software synthesizers (see Web Clip 1). The Hexpander tracked as fast as or faster than any other system I've tried. When I played rapid-fire runs, every note came through. But accuracy is more important than speed, and that's where the system really shines. I usually need to erase lots of errors when I record sequences with a MIDI guitar controller, but with the Ghost system, I've definitely noticed fewer false triggers. My only quibble is that I wish the system had an optional LED to let you know when it's working.
I also had a chance to try the system with an Axon AX100mkII interface. The Hexpander's circuit board has a tiny Traktion switch that optimizes the tracking curve for either Roland- or Axon-type converters. With a flip of the switch, I got the same excellent results using the Axon.
If you're considering retrofitting your guitar as a MIDI controller, Graph Tech's Ghost Modular Pickup System should be at the top of your list. Its modular nature allows you to tailor the components you choose to exactly what you want. Most important, it tracks with minimal latency and impressive accuracy. A guitar with a Ghost system installed is truly a capable MIDI controller.
We'll change the way you play!