/**
* > Add and overlap timestretch algorithm
*
* The overlap and add is the simplest, cheaper (in terms of computation) and
* less quality timestretch algorithm. It changes the length of a buffer without
* changing it's pitch.
*
* [](https://npmjs.org/package/dsp-ola/)
*
* This is part of [dsp-kit](https://github.com/oramics/dsp-kit)
*
* @example
* var ola = require('dsp-ola')
* const stretch = ola.overlapAdd({ size: 1024 })
* const halfSize = stretch(0.5, audioBuffer)
*
* @example
* var dsp = require('dsp-kit')
*
* @module ola
*/
import { zeros, gen, add, mult } from 'dsp-array'
const cos = Math.cos
const PI2 = 2 * Math.PI
const hamming = () => (n, N) => 0.54 - 0.46 * cos(PI2 * n / (N - 1))
/**
* Create a timestretch function using an overlap and add algorithm
*
* @param {Object} options
* @return {Function} the timestretch function
* @example
* const stretch = ola.overlapAdd()
* stretch(0.5, audio) // => a new audio buffer half of the length
*/
export function overlapAdd (options = {}) {
const { size = 1024, hop = size / 2 } = options
const window = gen(size, options.window || hamming())
const frame = zeros(size)
return function (factor, src, dest) {
var frames
// we change hop size in source to change the size of the dest
const srcHopSize = Math.floor(hop / factor)
const srcLen = src.length
if (!dest) {
// if not dest, create one
frames = Math.floor(srcLen / srcHopSize)
dest = zeros(frames * hop)
} else {
frames = Math.floor(dest.length / hop)
}
let read, write
for (var i = 0; i < frames; i++) {
read = src.subarray(i * srcHopSize, i * srcHopSize + size)
write = src.subarray(i * hop, i * hop + size)
mult(size, read, window, frame)
add(size, frame, write, write)
}
return dest
}
}