32 waveforms - LFO with 16 waveforms - MIDI clock sync
15 digital filter algorithms - Filter and pitch envelope modulation - Analogue bass boost circuit
2 ADSR Envelopes Pitch and phase LFO modulation - Wave crusher
16 memory patches - Filter, amplitude and pulse width LFO modulation - Phaser
Portamento - Arpeggiator with 15 sequences - Distortion
1/4″ mono jack - 12V power supply
3.5mm stereo headphones - 32 page colour instruction manual
MIDI input and output - Quick reference card
12V DC power supply - Free Atmegatron Librarian software available
6 pin header for programmer cable
The Atmegatron uses the Atmel 328P processor, which is also at the heart of most Arduino development boards. Audio is generated by modulating a PWM output of the processor and then filtering off the modulation frequency. The Atmegatron uses analogue circuitry in the form of a steep 3rd order Chebyshev filter to maintain the high end, while still filtering off the modulation frequency.
The Atmegtron’s software uses 2 loops to create it’s unique sound. One loop uses an interrupt to update the PWM output at audio frequencies. The other loop is slower and is used for everything else (MIDI input, process the wavetable, update LFOs, envelopes, arpeggiators etc). This unique synthesis method means that while the Atmegatron is clearly at home among classic Chiptune synthesizers, it also sounds highly individual.
The diagram below shows the wavetable processing chain. This is the structure of the Arduino code that is shipped in the Atmegatron, but this can be tweaked as much as the user desires and reuploaded using the Arduino development environment.