Shipping Of The Shruti-1 PCBs Will Start Shortly

If you plan to build a Shruti-1 synth you should hurry. Shipping seems to start very, very soon. BUT the PCBs and kits are limited only to a small amount.

Info via Mutable Instruments:

Old-school technology

Minimalist digital oscillators…

800MHz ARM core? Sharc DSP? Hardware-accelerated band-limited interpolation? Come on guys! The Shruti-1 runs on a modest AVR microcontroller (of the Arduino fame) clocked at 16 MHz and providing a whopping 2kb of RAM. You’re more likely to find this 8-bit wonder in vending machines than in synths… Yet, the Shruti-1’s firmware squeezes the most out of this tight processor to render classic waveforms, but also FM or weird digital sounds – all of them in their full 8-bit quirkiness.

... with an analog twist!

Today’s synths use DSPs or general purpose CPUs to emulate classic analog filters. To color and warm up your sounds, the Shruti-1 directly uses the real thing: a CEM3379 VCF/VCA, belonging to a lineage of chips found in the Prophet VS, my beloved Ensoniq ESQ-1 or the Waldorf Microwave. Perfect for fat basses or lively sequences.

DIY, Dudette!

The design is so simple you can build the Shruti-1 yourself. In fact, you’ll have to – the first units will be distributed as a kit. Hacking and experimenting with the Shruti-1 is easy – whether you want to connect an accelerometer or add a new synthesis algorithm to its OS.

Small and portable

It’s up to you to decide what kind of case you want to put the Shruti-1 internals in – but with a 10×7.5 cm main board, and a 10×6.5 cm controller board, this is certainly not going to be a 19” rack or a massive desktop module. Oh, and you can power it from a 9V battery.

No compromises

On musicality…

There are many cheap DIY noise-makers out there… but how many of them can you really compose melodies on, or use on stage to play sequences with? The Shruti-1 is by contrast a complete MIDI instrument. You can play it from a MIDI keyboard – the joys of weighted piano keys – or your favorite sequencer. As for the sound quality, we did our best to make it sound as little “cheap/chippy” as possible, and tried to cover a wide range of textures. Listen to some samples .

... and on features

Many features you expect to find on a professional synth – arpeggiator, patch memory, freely assignable modulations – are implemented. Some of the Shruti-1 features, like the step sequencer or the non-western tunings, are not even available on many synths manufactured nowadays. Have a look at the user manual to find out what’s there!


Digital/analog hybrid monosynth.

Digital oscillators

Available for all oscillators, and band-limited

impulse train (high-pass filtered square wave) with pulse-width modulation
square with pulse-width modulation
triangle with waveshapping
sawtooth with waveshapping
Available for oscillator 1 only

sawtooth with sweepable resonance (casio cz-like). This creates a resonance directly in the oscillator output, without using the filter
simplistic FM (1>2 configuration), with adjustable modulation index and frequency ratio
8bit-like harsh waveforms with wavetable scan
poor man’s square with pulse-width modulation (plenty of aliasing but fat for basses)
colored noise (sweep from low-pass filtered white noise -> white noise -> high-pass filtered white noise)
lo-fi vowel synthesis (think “speak and spell”) with vowel morphing
wavetable (16 waveforms) with wave morphing, for drones
“sweep” oscillator which scans through all the band-limited waveforms

adjustable oscillator balance
mixing algorithms: simple sum, simple sum with synchronization, ring modulator, xor modulator
extra sources: noise & sub-oscillator (triangle or square)

CEM3379 analog VCF/VCA, with external audio input

LFOs: 2, with square, sawtooth, triangle, sample & hold shapes. Syncable to tempo
envelopes 2 ADSR
modulation matrix: up to 14 source -> destination connections. Adjustable modulation amount in the -100% — 100% range
modulation sources:
LFO 1/2
step sequencer
arpeggiator gate
mod. wheel
pitch bender
DC offset
CV inputs 1/2/3
noise generator
ENV 1/2
note velocity
note number (eg for filter tracking)
keyboard gate
modulation destinations:
filter cutoff
VCA gain
pulse width/Parameter osc. 1/2
pitch osc. 1/2
vibrato (fine pitch, applied to osc 1 & 2 simultaneously)
oscillator balance
noise level
subosc level

step sequencer: 16-steps (4-bits value per step). Adjustable cycle length
arpeggiator: 15 rhythmic patterns, each of them with up/down/up&down/random variants. 1-4 octave range
clock: internal, 40-240 BPM with swing, or external (MIDI)
tuning: alternative tuning schemes/keyboard mappings: pythagorean scale, just temperament, 1/4 tone on E/A/B, Melakarta ragas
“patch performance”: custom page in which 4 user-selectable parameters can be assigned to the 4 editing pots
System and memory

MIDI implementation: notes, controllers, clock synchronization, patch editing by NRP, individual patch load/save by SysEx
patch memory: 16-patches stored in EEPROM
easter egg
firmware update by SysEx
Hardware and connectors

power: 2.1mm connector, requires 7.5V-9V 300mA supply (can be unregulated). Center pin positive (+), outer collar negative (-)
audio input/output: 6.35 Jack (Mono audio out), 6.35 Jack (External signal in)
cv inputs: 3 CV inputs (0-+5 V, labelled “HACK_ME!” on the PCB) for easy experimentation with controllers, accessible through pin header on the motherboard
MIDI: in, out (logical thru + patch dumps)
serial: tx/rx/reset pins for interfacing with an usb->serial chip, for on-chip firmware development
12 facade LEDs (current page / modulation matrix visualization)
backlit 2×16 LCD display
4 pots for patch editing
volume and input gain pot
5 navigation switches, one inc/dec switches pair