Tim Barrass

Currently your Arduino can only beep like a microwave oven. Mozzi brings your Arduino to life by allowing it to produce much more complex and interesting growls, sweeps and chorusing atmospherics. These sounds can be quickly and easily constructed from familiar synthesis units like oscillators, delays, filters and envelopes.

You can use Mozzi to generate algorithmic music for an installation or performance, or make interactive sonifications of sensors, on a small, modular and super cheap Arduino, without the need for additional shields, message passing or external synths.

• Available for a wide and growing range of MCUs, with and without inbuilt DACs: Arduino Uno R3 and R4, STM32, Teensy, ESP8266, ESP32, Raspberry Pi Pico, and more.
• Configurable sample rate, usually in powers of two (16384 Hz, or 32768 Hz).
• Variable control rate from 64 Hz upwards.
• Various inbuilt output modes, including 16 bit output to an external DAC.
• Allows interfacing to custom output routines, with examples for playing audio on external DAC modules, and even bluetooth.
• Useful basic audio toolkit: oscillators, samples, lines, envelopes, scheduling, filtering.
• Fast ADC and other cpu-efficient code utilities to help keep audio running smoothly.
• Example sketches for easy modification.
• Readymade wavetables and a script to convert your own soundfiles for Mozzi.
• Mozzi is designed to be easy to use, open source and extendable.

The easiest installation option nowadays is to install Mozzi via the Library Manager in your Arduino application: Arduino➞Sketch➞Include Library➞Library Manager type "Mozzi" into the search field, then click "install".

For other installation methods (e.g. the development version), see the Download page.

To hear Mozzi, wire a 3.5mm audio jack with the centre to the audio out pin for your Arduino as shown in the table below, and the shield to GND on the Arduino. Plug into your computer and listen with a sound program like Audacity. (Or connect any other high-impedance input, like an active speaker) Try some examples from the File > Examples > Mozzi menu.

For more about audio output, including high quality output modes Mozzi Output tutorial.

Mozzi 2.0 brings a lot of changes under the hood, and is not 100% source compatible with earlier versions of Mozzi. Most sketches should continue to compile, but with a lot of warnings. A few others will no longer work. See Porting to Mozzi 2.0 for what to change. If desparate, there is still a "Mozzi_1" branch in the git repository, but this will not get any new development.

Table is not necessarily complete. Abbreviations explained below the table. The default output mode is in bold for each row. If stereo is supported, in a mode, the cell PWM-1 has two numbers with the second pin number is given in parentheses (+X). Check the hardware section of the API-documentation for platform specific notes and (pin) configuration options.

• PWM-1: 1-pin PWM mode (MOZZI_OUTPUT_PWM)
• PWM-2: 2-pin PWM mode (MOZZI_OUTPUT_2PIN_PWM)
• PDM: Pulse density modulation, may be either MOZZI_OUTPUT_PDM_VIA_SERIAL or MOZZI_OUTPUT_PDM_VIA_I2S
• inbuilt DAC: MOZZI_OUTPUT_INTERNAL_DAC
• I2S DAC (native): native support for externally connected I2S DACs (MOZZI_OUTPUT_I2S_DAC). Since this requires several, often configurable pins, and is never the default option, no pin numbers are shown in this table.
• All platforms also support "external" output modes (MOZZI_OUTPUT_EXTERNAL_TIMED or MOZZI_OUTPUT_EXTERNAL_CUSTOM), which allow for connecting DACs or other external circuitry.

Here's a template for an empty Mozzi sketch:

#include <Mozzi.h>   // at the top of your sketch

void setup() {
	startMozzi();
}

void updateControl(){
	// your control code
}

AudioOutput_t updateAudio(){
	MonoOutput::from16Bit( [my_cool_sample] );
}

void loop() {
	audioHook();
}

There's a detailed example explaining the different parts here.

For getting started, browse the practical help on the learn page on the Mozzi site.
API reference documentation is available in the doc folder in the Mozzi download and online.
Start or look up a topic on the users forum.
Also, feel free to submit any issues on the GitHub Mozzi site.
Look for code and usage changes here.
For hardware specific details, including supported features, caveats, and hardware-dependent configuration options, refer to the Hardware Section of the API-Documentation.

• In most setups, Mozzi claims one or two hardware timers. This may result in incompatibilities with certain libraries, and / or the ability to use timer-based functions such as analogWrite(). As the details on this differ a lot between the supported boards, read up on the details - and available workarounds - in the ardware Section of the API-Documentation.

• There is also an example on emulating analogWrite() on any digitial pin in Mozzi>examples>11.Communication>Sinewave_PWM_pins_HIFI.

• The timers can be made available with stopMozzi(), which stops audio interrupts, until you call startMozzi().

• Note that it is of utmost importance to write non-blocking code, such that the audio buffer never runs low. Hints on how to do this, including why, and how you should avoid using delay(), analogRead(), and how to make your code run faster, can be found at on the learn pages.

External chips (DAC) can also be used on any platform which does not support natively the I2S protocol using an user defined audioOutput function. This can allow a greater audio quality over the native ways to output the sound (PWM for AVR Arduinos and STM32 and 12 bit DAC for Teensy 3.*). Examples are provided for the MCP492X DAC (12 bit on SPI) and for the (PT8211) 16 bit stereo DAC using SPI port to emulate the I2S protocol. The latter should be compatible with any DAC using I2S.

If you enjoy using Mozzi for a project, or have extended it, we would be pleased to hear about it and provide support wherever possible. Contribute suggestions, improvements and bug fixes to the Mozzi wiki on Github, or Fork it to contribute directly to future developments.

Mozzi is a development of research into Mobile Sonification in the SweatSonics project.

Modified versions of the following libraries are included in the Mozzi download:

TimerOne library
FrequencyTimer2 library - now a fork with support for ATmega32u4 processors

Mozzi has also drawn on and been influenced by (among many others):

xorshift random number generator, George Marsaglia, (2003)
ead~.c puredata external (creb library) Copyright (c) 2000-2003 by Tom Schouten (GPL2)
AF_precision_synthesis by Adrian Freed, 2009
Resonant filter posted to musicdsp.org by Paul Kellett, and fixed point version of the filter on dave's blog of art and programming
State Variable filter pseudocode at musicdsp.org and here
Various examples from Pure Data by Miller Puckette
Practical synthesis tutorials by Andy Farnell

Mozzi is licensed under a the LGPL version 2.1 or (at your option) any later version of the license.

Disclaimer: This is a human-readable summary of (and not a substitute for) the license.

• You may copy, distribute and modify the Mozzi library itself provided that you state modifications and license them under LGPL-2.1.

• You may distribute your own source code which merely uses the Mozzi-API under any licence that you wish.

• Regarding distribution of binaries (also inside a hardware project) that include Mozzi, the Arduino FAQ sums up the situation as follows: "Using the Arduino core and libraries for the firmware of a commercial product does not require you to release the source code for the firmware. The LGPL does, however, require you to make available object files that allow for the relinking of the firmware against updated versions of the Arduino core and libraries. Any modifications to the core and libraries must be released under the LGPL."

• Note that using third-party libraries/code - including as shown in some of the Mozzi examples - may introduce additional restrictions.