The instrument

The basis of Giraf is a polyphonic sampler where a sample can be played by hitting the “sound trigger” pad – the amplitude of the sound is determined by how hard the pad is struck. The pitch of this triggered sample can then be controlled by a infra-red distance sensor, in such a way that the further the hand is from the sensor, the lower the pitch. Instead of having continous control, the pitch that is actually played is determined in relation to a selected musical scale making harmonically related results easier to acheive.

Se a walktrough of the instrument in the video below:

Signal path and effects

The signal path of Giraf is as follows:

Alongside the main sampler Giraf has multiple built-in effects.

• FX1 – Sampler Gain
• FX2 – Biquad Filter
  • The button switches between: Bypass, Lowpass, Highpass and Resonant Bandpass
  • The knob controls the cutoff frequency.
• FX3 – Feedback Delay Line
  • The button switches the effect on/off
  • The knob controls the delay time
• FX4 – Reverberator
  • The button switches the effect on/off
  • The knob controls how much signal goes to the room
  • The action buttons playback the performance in reverse, with the right button resulting in normal pitch and the left button in double pitch and tempo
• The Looper:
  • When the green button is pressed once, sound is recorded until the button is pressed again, which starts overdub mode.
  • When no more overdubbing is required, the button can be pressed a third time to enable playback mode.
  • The red button clears the buffer and prepares the looper for a new recording.

Software and technical notes

The code implementation is written in C++ and it was programmed using the browser-based Bela IDE, which runs on a server on the Bela itself – no internet required. Using C++ and working with Bela allowed me to keep everything very fast and responsive. There was a total of ~66 samples group delay, that is - at 44.1kHz - 1.5ms of latency from trigger to the sound coming out: thank you Bela!!!

The Bela Blog

The project can be found on the Bela blog here: Giraf