Created by Bastl Instruments, Kastle is a pocket-sized, open-source synth that runs on three AA batteries. Although designed to be “DIY friendly and ideal for beginners,” it can also be combined with other small modular synths for enhanced functionality.
It produces unique modulations and lo-fi sounds, which can be very noisy and drony, soft or harsh. Kastle is powered by two ATtiny85 that can be reprogrammed with an Arduino — one chip is dedicated to sound generation, while the other handles the modulation. Several firmwares for the ATtiny chips are available.
The heart of the Kastle is a complex oscillator with three modes — phase distortion, phase modulation, and track and hold modulation. The oscillator section has three sound parameters pitch, timbre and waveshape — all under voltage control and with 5h433 different synthesis modes. It has a main output and a square wave output, both of which can be used independently or combined.
As its page explains:
The 3 synthesis modes are phase distortion, phase modulation (also known as FM) and track & hold modulation. Each mode utilizes two oscillators. The Pitch controls the main oscillator, the Timbre sets the pitch of the modulating oscillator and the waveshape depends on the synthesis mode. The waveshape also controls the pulse width of the square wave output from the main oscillator.
The voltage controllable LFO has a triangle and square output and a reset input. The stepped waveform generator is inspired by the Rungler circuit by Rob Hordijk. It can produce 8 different voltages either in random order or in 8 or 16 step looping patterns depending on how the BIT IN is patched.
Intrigued? You can check Kastle out on its page, as well as in the video below!