source: gs3-extensions/web-audio/trunk/js-mad/sink.js-master/src/utils/resample.js@ 28388

(function (Sink) {

(function(){

/**
 * If method is supplied, adds a new interpolation method to Sink.interpolation, otherwise sets the default interpolation method (Sink.interpolate) to the specified property of Sink.interpolate.
 *
 * @arg {String} name The name of the interpolation method to get / set.
 * @arg {Function} !method The interpolation method.
*/

function interpolation(name, method) {
    if (name && method) {
        interpolation[name] = method;
    } else if (name && interpolation[name] instanceof Function) {
        Sink.interpolate = interpolation[name];
    }
    return interpolation[name];
}

Sink.interpolation = interpolation;


/**
 * Interpolates a fractal part position in an array to a sample. (Linear interpolation)
 *
 * @param {Array} arr The sample buffer.
 * @param {number} pos The position to interpolate from.
 * @return {Float32} The interpolated sample.
*/
interpolation('linear', function (arr, pos) {
    var first   = Math.floor(pos),
        second  = first + 1,
        frac    = pos - first;
    second      = second < arr.length ? second : 0;
    return arr[first] * (1 - frac) + arr[second] * frac;
});

/**
 * Interpolates a fractal part position in an array to a sample. (Nearest neighbour interpolation)
 *
 * @param {Array} arr The sample buffer.
 * @param {number} pos The position to interpolate from.
 * @return {Float32} The interpolated sample.
*/
interpolation('nearest', function (arr, pos) {
    return pos >= arr.length - 0.5 ? arr[0] : arr[Math.round(pos)];
});

interpolation('linear');

}());


/**
 * Resamples a sample buffer from a frequency to a frequency and / or from a sample rate to a sample rate.
 *
 * @static Sink
 * @name resample
 *
 * @arg {Buffer} buffer The sample buffer to resample.
 * @arg {Number} fromRate The original sample rate of the buffer, or if the last argument, the speed ratio to convert with.
 * @arg {Number} fromFrequency The original frequency of the buffer, or if the last argument, used as toRate and the secondary comparison will not be made.
 * @arg {Number} toRate The sample rate of the created buffer.
 * @arg {Number} toFrequency The frequency of the created buffer.
 *
 * @return The new resampled buffer.
*/
Sink.resample   = function (buffer, fromRate /* or speed */, fromFrequency /* or toRate */, toRate, toFrequency) {
    var
        argc        = arguments.length,
        speed       = argc === 2 ? fromRate : argc === 3 ? fromRate / fromFrequency : toRate / fromRate * toFrequency / fromFrequency,
        l       = buffer.length,
        length      = Math.ceil(l / speed),
        newBuffer   = new Float32Array(length),
        i, n;
    for (i=0, n=0; i<l; i += speed) {
        newBuffer[n++] = Sink.interpolate(buffer, i);
    }
    return newBuffer;
};

}(this.Sink));