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When most people play with an Altura for the first time, their instinct is to wiggle their fingers and flap
their hands. This will produce chaotic results, which may be what you are after. However, for precise
melodic control, you must hold your hand flat and steady, and perpendicular to the axis of the sensor.
For stage drama, you might want to perform with paddles or dinner plates strapped to your hands.
We have pre-set the minimum and maximum distance over which the sensor is active, to optimize
playability and reliability. It is active from about 3" – 40" (8 – 100 cm). Any object in this range can
trigger the Altura: dangling cables, a passing guitar neck, a Marshall stack. Keep the play-zone clear!
Since the Altura uses sonar, and measures the speed of sound in air, its performance is somewhat
subject to atmospheric conditions. The active range will vary a little if you move between extreme
climates. These default range values can be changed if you hack the open-source software. See
"Programming The Altura" below. The sensors actually have a maximum range of about 4 meters! You
could use the Altura as a door bell, a motion-sensor alarm, or part of an interactive installation, where
Alturas are triggered by participants moving about the display space.
3. LEFT DISTANCE SENSOR – MIDI CONTROL FUNCTIONS
The left sensor generally determines a MIDI data value to send to the MIDI OUT. The data it sends is
determined by the FUNCTION currently selected. See "MIDI Function Select" on page 16.
When using Pitch Bend, removing your hand snaps the pitch back to No Bend, just like when you
release the Pitch Bend wheel on a conventional controller. When using the other functions, however,
removing your hand will fix the controller at the current value, like a slider. You set maximum and
minimum values with the DATA NEAR and DATA FAR knobs. See each FUNCTION section below for
details.
4. RIGHT SENSOR - MIDI PITCH
In Functions 1 - 5, the right sensor transmits Note-On messages. Whenever the Altura detects a new
note to send, it first turns off the current note by transmitting a "Note On, velocity 0"message.
The minimum and maximum distance over which the sensor is sensitive is pre-set to about 3" – 40" (8
cm - 100 cm). You can alter this by hacking the open-source software. See "Programming the Altura"
below. Holding your hand closer than the minimum distance can confuse the sensor and produce
unexpected behavior.
You can control how many octaves of notes are covered in the active range, from one to eight, using
the OCTAvE NEAR and OCTAvE FAR knobs. You can determine which way the notes range – from
low to high or high to low. See "Octave Near and Octave Far Select" on page 21 below. The more
octaves you select, the smaller the piece of air available for any one particular note. At one octave of
a pentatonic scale, each note gets about 6" (15 cm) of air, and they are quite easy to find. Six octaves
of a diatonic scale leaves only about ½" (1 cm) per note! The Altura software uses some clever trickery
to stabilize note selection, and minimize random fluctuations between notes. Nonetheless, you will
discover some practical limitations. There are more details in the OCTAvE section below.
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