srecord noeq AudioHaarFeature(IAudioSample sample, double start, double end) {
  double mid() { ret (start+end)/2; }
  
  double get(int channel) {
    double mid = mid();
    ret  sample.sampleSum(channel, start, mid)
       - sample.sampleSum(channel, mid, end);
  }
  
  Channels<Double> get() {
    ret mapChannels get(sample.channels());
  }
}