I have a navigation app that uses iOS's text to speech engine (AVSpeechSynthesizer / AVSPEECHUTTERANCE) for the turn by turn voice instructions. I have noticed during testing and now am getting a lot of user feedback that the voice volume is too low if they are playing music. I duck other audio already but still the voice volume is too low. This is especially a problem when playing over Bluetooth it seems. I'm already setting the volume of the utterance to 1.0 and have tried default ausiosession category and the new voiceprompt category. Neither works. I did some further research and found that other apps using the text to speech engine have the same problem EXCEPT Apple's own Maps app. Maps has a setting in Settings > Maps > Driving & Navigation to make the voice louder. I'm guessing Apple Maps is using some kind of private api??? This seems like an IOS bug to me and/or Apple has yet to publicize some method or variable to further boost volume. Documentation on the new voiceprompt audiosession category is still very limited at the moment Anyone seeing similar behaviour and/or know of a way or workaround to boost the volume?