Son of Stealth
The Son of Stealth MIDI Wind Controller
The Son of Stealth is a MIDI wind controller and is pictured above in prototype form. The term MIDI (Musical Instrument Digital Interface) denotes a standard method of digital communication between controllers and various kinds of synthesizers and other electronic sound-generating modules. Although MIDI is based on a note-on note-off paradigm that is most useful for keyboard controllers, it is versatile enough that it can also be used with wind controllers. A number of MIDI-based commercial wind controllers are now available, as are sound modules that respond well to breath control.
The following is a brief description of the SoS's main features.
Keyworks --Like the Stealth, SoS uses a side-by-side hand arrangement. Each keys consists of a flat spring with a plastic cap on the operating end and is mounted in a machined plastic block. Key travel is sensed with a magnet / Hall-switch combination. There are 15 keys, six for each hand and three for the left thumb. The fingering system is the same as for the Stealth: a C scale is the same as upper register clarinet, flutophone, etc., and each key (with two exceptions for interlocked keys) always changes pitch by the same interval.
Breath --A solid-state pressure sensor is used to measure breath pressure. The signal is processed by a series of circuits to produce three outputs (1) breath pressure mixed with an adjustable amount of "derivative" or "slope" signal, (2) a gate signal flagging breath pressure above a threshold level and (3) a retrigger flag that fires if a note is tongued before pressure falls below the gating threshold. The last of these helps articulate rapidly tongued notes and enables double- and flutter- tonguing.
Jaw --Bite force is detected by a combination magnet and linear Hall sensor attached to a U-shaped spring. The point where the ends of the U meet defines the center position for "tight-lip" mode. A switch selects either bipolar (tight-lip) or unipolar (loose-lip) output from appropriate analog circuitry, which includes an electronically produced dead zone for the bipolar case.
Benders --The right-hand thumb operates a pair of bowed spring strips that run parallel to the direction of the thumb. Thumb pressure is detected with linear Hall sensors, and a switch selects between bipolar and unipolar output. In bipolar mode the resting output is at midrange and one sensor increases the output while the other decreases it. This may be used for pitch bend or other centered MIDI controls. In unipolar mode the sensor outputs are added together.
Brain --All signal conditioning is done in the analog domain, so the controller's "brain" just needs to read the sensors and send out appropriate MIDI data. This is easily done with an integrated-circuit microcontroller. The PIC microcontroller used includes built-in analog to digital conversion and serial communication. The brain can also read a set of switches that are used to define the instrument's configuration, e.g., what information is sent to which MIDI parameter.