Synthberry Pi: Tutorial II - OSC Remote control

Published on Mar 7, 2020 Artis Lab

"SynthBerry Pi is the prototype of a standalone synthesizer based on the Raspberry Pi mini computer and the Pure Data development environment. The prototype is equipped with a control surface made up of eight potentiometers connected to the computer which allow to modify, in real time, the control parameters of the sound generation processes. Furthermore, by using the wireless connectivity of the mini computer, the Pure Data patches can be controlled by sending Open Sound Control (OSC) messages from devices such as tablets or smartphones.

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The video shows the remote control of a Pure Data patch based on Open Sound Control messages over the wireless network. On the phone we have chosen to use an application called Control which provides graphic interfaces equipped with objects which, in response to user actions, send OSC messages through the wireless connection.

For this demo we used a Pd patch that is based on a subtractive synthesis system. The patch consists of a white noise generator and four fourth-order bandpass filters. The eight potentiometers of the control surface allow to control, for each filter, the center frequency and the quality factor (Q). The filters have been tuned to operate in different frequency regions from the lowest, the pair of potentiometers on the left, up to the highest on the right.

Two interfaces have been developed in Control to change the parameters of the Pd patch which creates the subtractive synthesis system. The first interface is something similar to a mixer, since it makes possible to separately change the volume and position of the stereo panning of each of the four filters through the use of a widget that implements a multitouch interface. The vertical dimension of the graphic object has been associated with the volume control of each filter, while the horizontal direction allows the user to control the panning between the left and right channels.

The second interface has four buttons that allow the user to choose four different settings for the range of variation of the filter frequencies. The frequency value of the four filters is controlled by the position of the corresponding potentiometer by means of a mapping process in a well-defined frequency range defined by a maximum and minimum value. Each button of the Control interface recalls a different configuration in the patch for the extreme values (maximum and minimum) of the frequency regions in which the interpolation is carried out. Furthermore, by positioning the potentiometers all up or all down, it is possible to obtain precisely the values of the filter frequencies set for the different presets."

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