by Ernie » Mon Jul 15, 2019 8:13 pm
Testing US English, I don't hear a big difference in volume between Polly and iSpeech. Maybe different voices are more pronounced. Both also seem similar volume to Siri from what I've heard. What you might want to do is delete all your existing TTS sounds (you can do that in TTS screen) and re-download using all the same provider (Polly). I don't have way to increase the volume of Polly sounds.