Chrome: 69.0.3464.0 Canary

Steps to repro:
# Start Chromevox
# Open ChromeVox settings and set to use an Acapella tts voice
# adjust the pitch to below about 30% with search+shift+]
# Notice the voice begins to distort
# Lower the pitch to 0 and the voice is completely unintelligible

Expected: The lower pitch value should be about the same as 25%

Actual: You can lower the pitch beyond comprehension