Ecosyste.ms: Awesome

An open API service indexing awesome lists of open source software.

https://github.com/mildsunrise/simplejack

Simple, realtime JACK audio in Node.JS
https://github.com/mildsunrise/simplejack

audio jack nodejs real-time

Last synced: about 2 months ago
JSON representation

Simple, realtime JACK audio in Node.JS

Lists

README 

        
# simplejack



[JACK][] is a platform that enables sound applications to easily send and receive realtime sound from other applications or hardware.



This module enables you to register simple [JACK][] clients:



~~~ js

// Create the client

var simplejack = require("simplejack");

var client = simplejack("my-client");



// Register audio callback

client.callback(function(t) {

  return Math.sin(2*Math.PI * 440 * t);

});



// Start the client!

client.activate();

~~~



This will create a JACK client named `my-client`, with 1 audio port that

outputs a 440Hz tone. The `t` passed to the callback is the time in seconds since

the client was last activated, or the callback was last changed.



## Install



First make sure you have JACK v2 development files installed. On Debian/Ubuntu and

derivatives, you can do it with:



    sudo apt-get install libjack-jackd2-dev



Then install the module as usual, e.g.



    npm install simplejack



## Options



You can pass an object to `simplejack()` in order to customize options:



~~~ js

var client = simplejack({ name: "foo", forceName: true, ports: 2 });

~~~



The available options (and their default values) are:



~~~ js

{

  // Name of the client.

  name: "simplejack",



  // If enabled and a client with the same name exists, creation

  // will fail. Otherwise a unique name will be created.

  forceName: false,



  // Outgoing audio ports. If this is an array of strings,

  // the strigs are the names of the created ports.

  // If an integer N is passed, then N ports will be

  // created with names "out-0", "out-1", etc.

  ports: 1,



  // Mark the ports as "terminal", meaning the audio in these

  // ports is "original" and not available on any other port.

  // Synthesizers, hardware interfaces, etc. should set this flag.

  terminal: false,



  // Mark the ports as "physical", meaning these ports correspond

  // to some kind of physical I/O connector.

  physical: false,



  // Explicitely connect to the server with that name.

  // Otherwise JACK will try to guess or use "default".

  server: null,



  // If the server isn't started, fail instead of starting it.

  noStartServer: null

}

~~~



## Multiple ports



If you open more than one port, the second argument passed to the callback

is the index of the port for which the sample is being produced.



So, to produce a 500Hz tone on the first port and white noise on the other, do:



~~~ js

var client = simplejack({ ports: 2 });



client.callback(function(t, port) {

  if (port === 0)

    return Math.sin(2*Math.PI * 500 * t);

  else

    return 2 * Math.random() - 1;

});

~~~



## Implementation & limitations



**Disclaimer:** yes I know Node.JS is the worst platform to do realtime sound

processing because there's a single event loop and blah, blah, blah...



A buffer is kept (always with the correct size), on which samples are precalculated

and saved. When the "process" callback gets called for the first time, zeros are

returned, and we queue UV to calculate the next samples by calling the JS callback

and save them on the buffer.



The next time the "process" callback gets called the calculated samples on the buffer

are simply copied to JACK's output buffer, and the next samples calculation is

scheduled, and so on. If for some reason the samples aren't ready when the "process"

callback is called, zeros are returned instead.



When the client is deactivated the buffer is zeroed. FIXME



One of the problems with JS is that there aren't fixed integers, it's all floating

point numbers. And I decided to pass time in seconds instead of sample number,

which makes it worse. Consequence: you will loose a bit of precision in the time,

and thus in the generated samples. I don't think it's noticeable though.



[JACK]: http://jackaudio.org "JACK Audio Connection Kit"