few months back, I was looking for a way to downsample the audio data captured from mic using HTML5. I needed output rate as 12000Hz, if input was a direct multiplication of that (i.e 48000Hz) I had no problem, but it seemed complicated for other rates( e.g 44100Hz).
In these scenarios, direct down sampling( retaining only 1 out every 4) won't work, so I thought of interpolation, but stackoverflow had no solution at that time. So answering it myself.
the source of my solution.
the fiddle demo.
the code for interpolating arrays,
function interpolateArray(data, fitCount) {
var linearInterpolate = function (before, after, atPoint) {
return before + (after - before) * atPoint;
};
var newData = new Array();
var springFactor = new Number((data.length - 1) / (fitCount - 1));
newData[0] = data[0]; // for new allocation
for ( var i = 1; i < fitCount - 1; i++) {
var tmp = i * springFactor;
var before = new Number(Math.floor(tmp)).toFixed();
var after = new Number(Math.ceil(tmp)).toFixed();
var atPoint = tmp - before;
newData[i] = linearInterpolate(data[before], data[after], atPoint);
}
newData[fitCount - 1] = data[data.length - 1]; // for new allocation
return newData;
};
example of using it:
var originalArry = [1,5,3];
var newArry = interpolateArray([1,5,3],5);
