SLABS: Arrays of Pressure Sensitive Touch Pads



Arrays of pressure sensitive touch pads provide musicians with an expressive interface that can be mapped by software to behave in a variety of ways. The SLAB was designed to engage the body, to be both musically expressive and inspiring, to be easy to play at the entry level, and to be accepting of a lifelong development of virtuosity. Instead of discrete triggering mechanisms to start and stop musical events we chose continuous signal representations as the basis for the instrument. We chose Ethernet for I/O and wrote specialized Core Audio compatible drivers for OSX allowing us to send gesture data as audio data. As a consequence, gestures are tightly coupled to the sound.


One SLAB contains 24 touch pads and another has 32. We chose Interlinks’s VersaPad because of its pressure output. The x, y, and pressure of each pad is sent at 44.1 kHertz. On the SLABS32 there are 96 channels. Core Audio and Max/MSP handle this number of channels with ease using only a small percentage of the CPU. The data from the pad sensors is assembled in a Xilinx FPGA which also provides for an audio return path and connections to MIDI (Input Only) and Light Pipe. The SLABS use the Open Sound Control (OSC) protocol for programming a small display and two LED’s associated with each pad. OSC is sent to the host computer from the selector switches at the top of each column of pads.


Rimas Avizienis and Adrian Freed played a critical role in the development of SLABS.

Musical Examples on the SLABS Video

Performance by David Wessel and Nils Bultmann viola

The first example demonstrates how the instrument responds to gestures. The
point to be made here is that gestures are treated as signals at the audio rate
providing a tight coupling between the performer and the sound.

The second example has each pad control the speed of two identical percussion
loops. The mapping between the Slabs controller and the sound producing
algorithm is done in Max/MSP.

The third example uses a form of granular synthesis in Mac/MSP. A sound file is
associated with each pad on the 24 pad controller to Wessel’s left. The position
in the file from which the grains are extracted is controlled by the x-axis and the
scatter of the grains is controlled by the y-axis.

The fourth example features Nils Bultmann on viola. The sound files associated
with the 24 pad controller and its granular synthesis algorithm were obtained from
processed recordings of the viola.

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Slabs32.JPG1.69 MB
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Re: SLABS: Arrays of Pressure Sensitive Touch Pads

David Wessel
Professor of Music
Co-Director CNMAT
wessel [at] cnmat [dot] berkeley [dot] edu

Slabs32.JPG1.69 MB