Mutable Instruments Shruti-1 with SM4 filter Assembled

via this auction

"What is it?
The Shruthi-1 is a hybrid digital/analog monosynth. Its hardware design is deceptively simple, but the sonic range is wide: sometimes grungily digital like a PPG-Wave, fat and funky like a SH-101, videogame-y like a Commodore 64, weird and warm like an ESQ-1 ; but more often than not, truly original.

Best of both worlds
Digital…
An 8-bit microcontroller plays the role of the two main oscillators + sub-oscillator. This allows the generation of (aliasing-free) classic analog waveforms, but also wavetable/transwave synthesis and a trove of weird digital algorithms (sinewave bitcrushing, formant synthesis, phase distortion, bit toggling, XOR modulation).

... and Analog

Beyond this point, everything is analog. Most of the Shruthi-1s are built with the SMR-4 filter, a warm 4-poles “modern analogue” low-pass (no vintage IC). But you are in no way limited to this! The filter section of the Shruthi is on its own board and can be easily replaced. We currently offer 2 alternatives filter boards, one with the CEM3379 VCF/VCA chip of the Ensoniq/Waldorf fame ; and one with the classic SSM2044 VCF. More to come, based on vintage chips or modern OTAs and VCAs! From silky-smooth to squelchy or fat: pick the filter that matches your personal taste best.

The Shruthi-1 has an audio input: external signals can be processed by its analog section, under the control of the digital LFOs, sequencer and arpeggiator for crazy gating and re-enveloping effects. A perfect way of warming up the sound of your favorite VA or… cheesy organ!

Before all, a musical instrument

Designed as a tool, not a toy

Getting a microcontroller to make bleeps and bloops is easy, but this is not where we wanted to go. We took the challenge of creating an instrument that could play in the same league as a Waldorf, Ensoniq or DSI synth; and from what Shruthi-1 users can attest, we have succeeded. Gameboys and Prophet-VS’ both ran on 8-bit cores. Guess what inspired us…

Of course, you are free to use the “dirty PWM” or “8-bits” oscillators algorithms if nasty bleeps are what you are looking for!

Feature-packed

We have packed the Shruthi-1 firmware with plenty of great features: a complete MIDI implementation (large CC coverage, NRPNs, SysEx data dump including wavetable transfer), a 12-slots modulation matrix, a 16-steps notes/CC sequencer and advanced arpeggiator with some unusual time warping modes, and even a polychaining feature to turn several Shruthi-1s into a monster polysynth!

Hackable

Open…

The Shruthi-1 firmware is GPL. Schematics are released under a CC license which gives you the freedom to build your own synth. We also provide assembly instructions, BOMs with references, case drawings, and some analyses of the filter circuits.

... and low barrier to entry

Posting code and schematics is not all… The Shruthi-1 has other great assets that make it a cool hacking platform:

A readable, well-structured code-base in C++, relying on a freely available toolchain.
Schematics editable with the freeware version of Eagle.
An easy firmware update procedure: just press a button and play a midifile to upgrade your Shruthi.
Solid foundation for developing your own analog filters, modulations and effects circuits. We provide PCB templates and an experimentation board to get you started on the design of the next Shruthi-1 filter board!
So get ready for new filter boards or hardware extensions!

This is from the second batch of Shruti-1's that went on sale the other week. It was hand assembled and tested by geargasstore in our shop. It comes with the clear acrylic case with honeycomb patterns on the sides."