A distinctive characteristic of many traditional wind instruments is the ability to shape the sound by "shading" toneholes with your fingers. WARBL's infrared optical sensors detect how far a finger is from each tonehole, and WARBL uses the sensor information to send MIDI pitch-bend messages that allow for realistic slides and vibrato. Algorithms for cancelling the affects of ambient light mean that the sensors are accurate in nearly all lighting conditions.

WARBL uses breath pressure to allow "overblowing" to jump to the second octave, making playing easy and intuitive. In fact, WARBL is in many ways easier to play than actual wind instruments. Constant monitoring of breath pressure and sophisticated modeling detects the player's intentions by responding to breath or a bagpipe bag in a natural way. Settings can be changed to simulate the way that a variety of instruments respond to overblowing, or you can choose to be limited to one octave (like with a bagpipe chanter). Alternatively, you can play without using the pressure sensor, instead using a button click to start and stop the sound.

A feature of the WARBL pressure sensor is that it is a closed system, so no air escapes. This means that you never have to take a breath or refill a bagpipe bag. While this generally makes playing easier, it also changes the way that breath can be used for articulation. If preferred, a mouthpiece with a small hole can be used to let air escape and more closely approximate a real instrument.

WARBL was designed to be affordable by using a simple, universal design. It uses a sturdy 8 1/2" by 5/8" acrylic enclosure. The pressure sensor has a moisture trap and a 1/4" tube for the mouthpiece that can be removed and replaced with a bagpipe-bag attachment. The hole spacing is similar to that on a D tin whistle, but also has a left-hand thumb hole and a right-hand "pinky" hole, enabling many fingering pattern options. There's even an optional "bell" sensor that plugs into the bottom end to simulate playing uilleann bagpipes "on the knee".

WARBL draws power from a host device like an iPad or PC, so no batteries are needed. Every attempt was made to reduce power consumption, and WARBL only uses 20mA of current, even while reading all ten sensors at a rate of 1000 times per second. This rate provides a high degree of responsiveness and no noticeable latency.

WARBL produces no sound on its own, instead sending MIDI messages to apps that produce the sound. This allows more control over customizing sounds, and also helps reduce complexity, cost, and power consumption. The WARBL firmware can be easily upgraded, and the entire design is open source, for those who are interested in tinkering with it.

In the interest of keeping the hardware design simple but functional, WARBL has limited onboard controls (three buttons and an LED indicator). Instead, the Configuration Tool web app (also available as the WARBL iOS app) can be used to calibrate the sensors and customize the device by reprogramming the buttons, controlling pitch bend, and changing the response to air pressure. You can store settings for up to three different "instruments" and recall them at any time.