Auduino

     

Auduino Release status: beta [box doku]
Description	Simple Arduino based synthesizer
Author(s)	tiefpunkt
Download	https://github.com/tiefpunkt/Auduino

The Auduino is a small synthesizer, based on the Arduino. The only external components required are 5 potentiometers, and something to output the sound, such as a small speaker, or a headphone jack.

Hacks

Modify the scale

By default, the Auduino uses a pentatonic scale. That can be changed in the source. An external switch to change the scale during runtime would be awesome.

Below are the options, only one is executed during runtime.

 // Smooth frequency mapping
 //syncPhaseInc = mapPhaseInc(analogRead(SYNC_CONTROL)) / 4;

 // Stepped mapping to MIDI notes: C, Db, D, Eb, E, F...
 //syncPhaseInc = mapMidi(analogRead(SYNC_CONTROL));

 // Stepped pentatonic mapping: D, E, G, A, B
 syncPhaseInc = mapPentatonic(analogRead(SYNC_CONTROL));

Adding some if-clauses, dependend on digitial inputs might be a decent solution.

Delay

Here's an example on using a ring buffer as a delay: http://rcarduino.blogspot.de/2012/11/auduino-with-delay.html

Maybe that could be added as an option as well.

CV Inputs (for sequencers)

CV Inputs are now done using 3.5mm jacks with integrated switches. They are placed between the potentiometers and the analog inputs of the Arduino. When a plug is inserted, the potentiometer gets disconnected from that particular input.

Next steps are to add some input over-voltage protection in the form of zener diodes, and maybe a possibility to use 0-10V CV.

A gate input would be great as well.

Adapt the Scales to 1V/Octave

On "old" analog synth hardware, 0-10V CV was used, with 1V/Octave. Not sure if the current scale reflects that, but it would be cool if it did, otherwise it might be wise to adjust this. However, in our case it would have to be 0.5 V/Octave

Line Level Output

By default, the Auduino outputs a PWM-signal between 0 and 5V. We want to adapt this down to line level, which according to the web is between -0.5V and 0.5V. So it needs some kind of filter and pad on the output. We put together something simple with only 3 parts. See the circuit below

PWM to Line level audio filter

Note: Dave from Notes And Volts has done some further optimization on the filter: Build the Auduino Granular Synth - Line Level Upgrade

Headphone out

Add a headphone output to the line output.

Versions

v0 Breadboard Prototype

First version, using fullsize Arduino Clone, and some potentiomenters on breadboard. Used it to try out different filters for the PWM signal, as well as some software mods. Picture

First prototype

v1 on perfboard

Version on perfboard in a "case". Built using an Arduino Pro Mini 5V 16Mhz. Has 5 CV inputs (3.5mm jacks), and audio filter built in. Post on Tumblr

The whole thing from the top

Protoboard from top

Frontpanel from the back, with connector

Running the synth with a simple sequencer

The pictures are missing the switch to select the scale, which was added a little later.

Links

• Auduino Homepage
• Audoino Step Synthesizer (includes a good explaination of what's actually happening inside the synth)