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Axoloti Core Synthesizer

   (1 review)

“Axoloti Core” is a circuit board with stereo audio in- and output, audio analog-to-digital and digital-to-analog converters and a microcontroller suitable for digital audio processing. All connectors are on one side to make it easy to build your own tabletop device, rackmount, stompbox or something else.

Connect to your PC or Mac, and start patching with the Axoloti Patcher. Disconnect from your PC and play your patch. The Axoloti patcher is the software part of Axoloti, and is a workbench to compose and edit your sound algorithms and interactions. After editing, patches can be stored in the Axoloti Core, and run without a computer connection.

The Axoloti patcher object library currently offers oscillators (sine, alias-free saw, square, pwm, some noise generators, FM modulation), 1st order and 2nd order filters, envelopes, LFO’s, tables, Midi I/O, analog voltage input, PWM output, and streaming wave file playback from SDcard.

The Axoloti patcher is written in Java and works on Windows (7 or later), OSX (10.7 minimum) and Linux. This GUI actually generates C++-code from the patch, then uses GCC to create binary executable code, and uploads the executable to the microcontroller, with one single mouse-click. After uploading, the patcher “locks” the patch architecture, and parameters in the patch can be adjusted in real-time on the screen (or from a midi controller).

Axoloti Patcher features:

+ Seamless edit/compile/upload/adjust with a simple “live” button
+ Wire datatypes for booleans (yellow), integers (green), fractional numbers (blue), and audio fractional number buffers (red)
+ Seamless readback of live data in the patch: VU-meters, chart plotter, oscilloscope, spectrum analyzer…
+ Object “input type overloading”: objects can adapt to the type of connected inputs
+ Object selector with search
+ Cut/copy/paste (using plain text XML)
+ Midi mappable controls
+ Parameter modulation
+ Sub-patching (using a patch as an object in another patch)
+ Presets
+ Midi polyphonic voice allocation
+ Axoloti object library:

+ audio input
+ audio output
+ digital in (including optional pullup or pulldown configuration)
+ digital out (push-pull or open-collector)
+ analog in
+ digital PWM outputs

+ sine
+ saw
+ square

+ sine
+ saw
+ square
+ pulse-width modulation
+ saw with sync
+ square with sync

+ AR

+ lowpass biquad
+ bandpass biquad
+ highpass biquad
+ lowpass 1st order
+ highpass 1st order

+ controller in
+ controller out
+ keyboard (incl. velocity, release velocity, polyphonic pressure)
+ bend in
+ bend out
+ channel pressure

+ 1,2,3,4… channel input mixer
+ crossfader

Logic operators
+ Tables - similar as in Pure Data

+ Echo
+ Delay lines - similar as in Pure Data
+ Soft saturate (non-antialiased)
+ infinite gain clipping (alias-free)

+ VU-meter
+ chart-plotter
+ oscilloscope
+ bandpass-filter based spectrum analyzer (constant-Q)
+ FFT-based spectrum analyzer

+ Logarithm
+ Exponent
+ Square root
+ Reciprocal
+ Sine/cosine

Hardware Specs:

+ Assembled circuit board
+ 168MHz STM32F427 microcontroller
+ 24bit/96kHz capable stereo audio ADC/DAC (editor and firmware currently only supports 24bit/48kHz)
+ 8MB SDRam
+ On-board switching power supply
+ Circuit board dimensions: 160 x 50 mm
+ 3mm mounting holes
+ Board revision 1.1
+ Assembled and tested in Belgium

+ 1/4″ stereo input jack (line level with up to 55 dB digitally-controlled analog gain)
+ 1/4″ stereo output jack (digitally-controlled volume, DC-coupled)
+ 1/8″ headphone jack (same sound as the stereo output, independent volume)
+ MIDI input (5-pole DIN)
+ MIDI output (5-pole DIN)
+ Micro-SDCard slot
+ Micro-USB device port
+ Full size USB host port, supports USB-MIDI compliant devices. USB Hubs are not supported!
+ DC input (7-15V, 2.1mm center pin, center pin positive)
+ Solder pads for connecting potentiometers, faders, switches, LED’s… (16 signals, ground, 3.3V supply, 5V supply).
+ All I/O is 3.3V signalling.

Technical Specifications
Type: Digital
Synthesis: Frequency Modulation, Subtractive
Oscillators: *
Waveforms: Pulse Variable, Saw Down, Saw Up, Sine, Square, Triangle, White Noise
Osc Modulation: Continuous Controller, Envelope, Keyboard, Knob, LFO, Oscillator, Ring Modulation, Sequencer, Sync Hard, Velocity
Oscillator Notes:
The number and types of oscillators are patch independent.
Envelopes: *
Evelope Paramerters: Attack, Decay, Sustain, Release
Envelope Notes::
The number and types of evelopes are patch independent.
Filters: *
Types: Band Limit, Band Pass, High Pass, Low Pass, Resonance
Filter Modulation: Input, LFO, Oscillator, Sequencer
LFO: *
LFO Parameters: Saw Up, Sine, Square
Polyphony & Tuning
Polyphony: *
Timbrality: *
Tuning: Standard
Modes: Mono, Polyphonic
Storage: Micro SD, USB
Editing: USB
Delay, Distortion
1 - 16 step modules
Case: Desktop
Case Details: Core circuit board requires user built case.
Controls: Modulation - Audio Input, Buttons, Switches
Display Type: LED
Dimensions (WxDxH): 17 x 6 x 3 cm
Weight: 75 g
Audio Output Connections: 1/4" Phone Jack, 1/8" Phone Jack, Stereo Main, Stereo Headphone
Power: 9V DC
Year Released: 2015

Product Links
Company Product Sites:
[+] www.axoloti.com
Repairs and Support
[+] community.axoloti.com
Editors & Software:
[+] www.axoloti.com
MSRP List Price: €65 - convert

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Jack Hertz

   1 of 1 member found this review helpful 1 / 1 member

I love this synth. Those who are familiar with PD, Nord Modulars, and any number of digital modulars, will be up and patching in just 10 minutes.

Don't be fooled by that little board. It has been very well thought out with many of the things people have wanted in a DSP hardware synthesizer. While a circuit board seems a bit cumbersome, it has allowed the designer, Johannes Taelman, to focus on functionality and development of the Core system, while leaving choices for DIY and or aftermarket cases to the community and its users. In this regard, Axoloti has done a great job of using the open source model to create something that truly is by everyone, for everyone, and at a low price. This never happens, thus I have given the Axoloti the coveted 5th star for doing it right.



The Axoloti is especially nice with the MusicThing case and controller kit now available. The easy to assemble kit, transforms your naked Axoloti board into the most delicious little sound sandwich you ever heard. The very clever design takes advantage of the harness on the PCB to add real controls including: 5 knobs, 3 buttons, and a tiny joystick. All on the same footprint as the Axoloti board. The nicely priced kit is about $60 USD without board, $120 with (when in stock), shipped.



The board features an amazing number of module choices, that needs some knowledge of modular synthesis and working with summed modulation routing. The Patcher has no normalization, not a bad thing. You will need to work in some gain stage controls and filtering of modulation lines as things can easily go out of bounds.

The Patcher environment shown below demonstrates the Axoloti can be used for some very large patches. There are all the traditional modules like Oscillators, Envelopes, Filters, LFOs, Mixers and Sequencers. Some in different types, such as stepped and matrix sequencers. Additionally, the Patcher includes logic Tables modeled on PD, as well as Math functions for comparisons and decision making.

What's even more interesting, is the ability to call other Patches as objects from within a patch. This is an extremely powerful feature that enables the sound maker to build a library of objects they can continue to work on and improve, without having to rebuild the old patches. This option also opens an opportunity for people to share objects as well as patches with each other.



With so much on hand, there is the opportunity here to create whatever you need in a synthesizer. In the digital realm, when you need one more OSC or other module to do things one better, it is always there for you to add. Within reason, of course. Already, there is a generous library of patches available including ARP 2600 emulations, FM synthesizers, MIDI Sequencers, Poly Synths, Drum Machines, Digital Effects, and you name it. That is the whole idea of the Axoloti.

One of the features that is easy to overlook are the physical MIDI IN and OUT ports. This effectively offers a full modular MIDI environment that should be able to talk with anything that has a MIDI port. With this, we can go wild with all manner of sequencers, random data generators, and generative patches that can send note, velocity, aftertouch, pitchbend and even dynamic patch changes, with a bit of ingenuity.

How does it sound? With 24-bit audio, in and out. This is a great sounding full spectrum audio synthesizer. It can create lush pads, horrific noise and everything in-between. As mentioned before, the lack of normalization between modules means you can take things to the extreme, if you want to. Still, the Axoloti is reference quality for working with FM and things that need precision. Using the Patcher for downloading sounds to the synth can be a little tricky, but it works with practice. With a MicroSD for storage, you can load 1000s of patches and even stream audio files from a card as large 64 GB, for nearly infinite storage.


For the €65 / $70 USD price, this is an amazing bargain for a super-powerful self-contained synthesizer - Even with having to make your own case. Which, is not so hard to do via a generous harness ready to connect knobs, buttons, and anything else you can dream of. Don't be afraid of the board, get the MusicThing kit or roll your own.

Those looking for an affordable modular system, the ability to work with huge patches, a core system to design a custom synth, or a way to experiment with sound design and MIDI, will find the Axoloti Core to be a great starting point to realize their ideas.

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