LibSynth

A simple drop-in MIDI synthesizer library for Linux.

Ever needed to programmatically play notes? Bought a MIDI keyboard to create fun sounds but don't really need a DAW? This is the library for you: start hearing sound in two lines of code.

Requirements

This requires ALSA, thus it only works on Linux systems. Debian-based systems like Ubuntu can install the ALSA bindings with the following command:

sudo apt install libasound2-dev

Installation

This library is built using the standard make && make install loop.

To compile the library:

make

To install the library:

sudo make install

To make the example synthesizer and hear some playback immediately:

make example
./synth -p acid

How do I use this to play notes or make sounds?

Right now there is no real documentation, but the interface is meant to be dead-simple. I recommend looking at the example program in the examples directory which can be built using make example.

Simply include <Synth/Synth.hpp>, link with -lsynth and make a Synth object.

Each Synth object spawns its own audio thread in the background. To play a note call the noteOn method which accepts an integer note and a velocity, representing how 'hard' the note was played, e.g. how hard the key was pressed on a keyboard or hit on a pad -- 1.0 being hardest, 0.0 being softest.

Calling noteOn is effectively the same as pressing and holding down a key on a keyboard. You need to call 'noteOff' to release the note.

To make sounds this is all you need to know, but there are more knobs to adjust: It features the standard ADSR envelope along with a low pass filter and an ADSR envelope for that filter.

I have a MIDI keyboard, how do I use it?

Once you've installed ALSA and it's utilities (see above), make sure your keyboard is plugged in. Then call aconnect -l from the command line to list currently connected devices. Here's some example output from my terminal:

client 14: 'Midi Through' [type=kernel]
    0 'Midi Through Port-0'
client 24: 'MPKmini2' [type=kernel,card=2]
    0 'MPKmini2 MIDI 1 '
client 28: 'Virtual Raw MIDI 3-0' [type=kernel,card=3]
    0 'VirMIDI 3-0     '
client 29: 'Virtual Raw MIDI 3-1' [type=kernel,card=3]

My keyboard is the MPKmini2 keyboard so I provide that string name to the Synth class on instantiation, e.g. Synth synth("MPKmini2"). And that's it. You should be able to play notes on your physical keyboard and hear it on your speakers.

Using the example program, I can run ./synth -d MPKmini2 to play notes with my keyboard as well.

Limitations & TODO

Although the scope of this synthesizer is meant to be small and not replace a DAW in any capacity, there's still many things that would make this better such as:

* A low-frequency oscillator
* A simple software arpeggiator 
* Simple drum machine (a special low note arpeggiator, I guess...)
* Support more than 2 channels
* Support other sample rates -- only supports 44100Hz right now (CD Quality)
* Documentation

Shout Outs

This was a fun project. I wanted to make it because there's simply no drop-in libraries that I could find where I could just play notes programmatically while also using my keyboard. I just wanted to make beep boop.

Special thanks to the tutorials of Martin Finke and the book BasicSynth by Daniel Mitchell.