Merge change 21226 into donut

* changes:
  Fix bug 2046705 where the output of the speech synthesizer is too low. The language files for the SVOX Pico engine result in the output of the synthesizer to be too soft, and barely audible on a phone speaker. The change implements a low shelf filter on the output of the synthesis and a drastic amplification. This works as intended because the synthesized data contains too much energy in the lower frequencies that is wasted on a phone speaker. Once filtered out, they leave room for amplication to address the volume issue.