load multiple files via XHR, then run a callback

loadSamples.coffee

    loadSamples: (urls, callback) ->

      loaded = []
      requests = []

      decode = (_raw) =>
        @audio.decodeAudioData _raw, (sample) ->
          loaded.push sample
          callback(loaded) if loaded.length is urls.length

      for url, i in urls
        requests[i] = new XMLHttpRequest()
        requests[i].open 'GET', url, true
        requests[i].responseType = 'arraybuffer'
        requests[i].onload = ->
          decode this.response
        requests[i].send()

And if you want to keep track of them (by using an object instead of an array),

    # define the loader function
    loadSamples = (requested, callback) ->

      loaded = {}
      XHRs = {}
      audio = @audio

      decode = (_name, _raw) =>
        audio.decodeAudioData _raw, (sample) =>
          loaded[_name] = sample
          callback(loaded) if _.size(loaded) is _.size(requested)

      for name, url of requested
        XHRs[name] = new XMLHttpRequest()
        XHRs[name]._name = name #meh
        XHRs[name].open 'GET', url, true
        XHRs[name].responseType = 'arraybuffer'
        XHRs[name].onload = ->
          decode this._name, this.response
        XHRs[name].send()

      # define the samples
      samples =
        vox: "/audio/120_1Bar_VoxSample4ChokeTest.wav",
        tick: "/audio/CLK_LOGICA.wav",
        tock: "/audio/CLK_LOGICB.wav"

      # call the loadSamples function & pass results into a callback function
      loadSamples samples, @makeSomethingThatUsesAudio