James Grahame, principal designer and developer
Nathanael Jeanneret, front panel illustration

Jarek Ziembicki – Created the original AVRsynth, upon which this project is based.
Laurie Biddulph – Worked with Jarek to translate his comments into English, ported to Atmega16
Daniel Kruszyna – Extended AVRsynth (several of his ideas are incorporated in MeeBlip)
Julian Schmidt – Filter algorithm
Peter Kirn, Create Digital Music, documentation

The MeeBlip story starts in 2002, when Jarek Ziembicki built his AVRSYN synthesizer around an Atmel AT90S8535 microcontroller. His elegantly simple design incorporated two oscillators, a simple filter, an AR/ASR envelope generator and an LFO. Instead of an expensive 16-bit DAC, he opted for a resistor ladder to generate audio output. The project was eventually ported to the newer Atmega16 microcontroller by Jarek and Laurie Biddulph, who released it in kit form.

Jarek’s creation inspired Daniel Kruszyna to add some interesting features to the original. He envisioned it as a poor man’s Chameleon, and his software added wavetable oscillators and several different kinds of filter.

My goal when creating MeeBlip was to keep the design simple while making it as compatible as possible with Jarek and Daniel’s original software. A key part of the synth’s simplicity is the addition of on-board controls, instead of requiring a hand wired array of switches and knobs. MeeBlip incorporates a dual 8-bit weighted DAC and a 4-pole lowpass anti-aliasing filter for higher quality sound, while remaining affordable and easy to build. The result is an inexpensive AVR audio plaftorm that fits on a single board.

The MeeBlip software extends Jarek’s original vision by adding an ADSR envelope, variable oscillator mix, noise waveform and a bank shift mode that allows two parameters to be intelligently mapped to each knob. Daniel implemented simple 2-operator FM in his avrsyn code, which I managed to squeeze into MeeBlip as well.

However, much of MeeBlip’s distinctive musical character stems from the addition of a 2-pole resonant filter. It’s based on previously unreleased code by Julian Schmidt of chipmusik.de, who used hard clipping to create a musical sounding filter without requiring 24-bit (or higher) math that would have pushed an 8-bit microcontroller beyond its limits. With the addition of some performance-optimized math routines that would make a DSP engineer cringe, the entire system runs at a 40 kHz sample rate.

I owe sincere thanks to Jarek, Daniel and Julian for their enthusiastic support of this project, and hope that MeeBlip inspires others to build upon our work.

James Grahame
November, 2010