README

lowpass

Simple nodejs Audio manipulation library, based on node-wav

This module offers basics nodejs manipuji

LowPass : fast and basic (moving average-based) low pass filter
Cutter : Basic Stream to handle mp3 streams
Wav2energy : Transform
getBPM : soundstretch wrapper for nodejs
getBuildUp : Build-up detection (when music energy is more than a defined threshold)

Combined with node-lame it can also manage mp3 files.

Installation

Install through npm:

$ npm install lowpass

Example

Here's how you would use the lowpass filter on a standard PCM WAVE file out of the speakers using node-wav and node-speaker :

var fs = require('fs');
var wav = require('wav');
var Speaker = require('speaker');
var LowPass = require('lowpass').LowPass;

var file = fs.createReadStream('input1.wav');
var reader = new wav.Reader();

var speaker, lowpass;

// the "format" event gets emitted at the end of the WAVE header
reader.on('format', function (format) {
  speaker = new Speaker(format);
  lowPass = new LowPass({format : format});

  // the lowpass is piped between file reader and speaker
  reader.pipe(lowPass);
  lowPass.pipe(speaker);
});

// pipe the WAVE file to the Reader instance
file.pipe(reader);

Same example with mp3 file and the node-lame package

var fs = require('fs');
var wav = require('wav');
var Speaker = require('speaker');
var LowPass = require('lowpass').LowPass;

var file = fs.createReadStream('input.mp3');
var lame = require('lame');

var speaker, lowpass;

// start reading the MP3 file from the input
var decoder = new lame.Decoder();

// we have to wait for the "format" event before we can start encoding
decoder.on('format', onFormat);

// and start transferring the data
file.pipe(decoder);

function onFormat (format) {
  speaker = new Speaker(format);

  lowPass = new LowPass({
    format : format
  });

  // write the decoded MP3 into the lowpass filter then the speaker
  decoder.pipe(lowPass).pipe(speaker);
};

LowPass()

The LowPass class accepts the data from node-wav outputs the raw audio data transformed by the low pass.

it has the following options :

var LowPass = require('lowpass').LowPass;

//First form
new LowPass({
    format : format, //format from node-wav, mandatory option
    movAvLength : 128 // moving average window
});

//Second Form
new LowPass({
    format : format, //format from node-wav, mandatory option
    movAvLength : 152 // Hz
});

By default the cut-off correspond to a 128 length moving average window. For a 44100 sampleRate, it is equivalent to 152Hz low pass filter.

getBPM()

The getBPM function call soundstretch utility to get the BPM of a song.

var getBPM = require('lowpass').getBPM;

getBPM("input.wav", function(err, bpm){
    console.log("BPM is ", bpm);
});

Be carefull, soundstretch must be installed in your system.

Other tools

See examples

Thanks

Thanks to TooTallNate for the published libraries

Usage no npm install needed!