gistfile1.js

var spawn = require('child_process').spawn,
  temp = require('temp');

Audio.prototype.slowDown = function rb(options, input, cb) {
  var speed = options.speed,
    s = (this.isNumeric(speed) ? Math.pow(speed, -1) :
      this.error('speed needs a number')),
      slow = null;

  console.log('if this prints it will work');

  temp.open('rbIN', function (err, infile) {
    if (err) {
      return cb(err, null);
    }

    input.pipe(fs.createWriteStream(infile.path));

    input.on('end', function (data) {
      temp.open('rbOUT', function (err, outfile) {
        if (err) {
          return cb(err, null);
        }

        slow = spawn('rubberband', ['-t', s, infile.path, outfile.path]);

        slow.on('exit', function (code) {
          if (code) {
            return cb('error, exit code: ' + code, null);
          }
          if (!code) {
            console.log('successful write out to: ' + outfile.path);
            //return cb(null, fs.createReadStream(outfile.path));
          }
        });
      });
    });
  });

};