The voice quality of Siri was really shitty after I updated to iOS 11*. The voice sounded highly robotic and not natural at all, when it was supposed to sound more natural according to a number of news articles I found. That was particularly annoying for driving directions, where the low quality voice is really annoying over the car’s stereo system.
It turns out that the voice that I was hearing was “Samantha”, the voice-over standard, and the solution for me was to go to (take a deep breath) Settings / General / Accessibility / VoiceOver / Speech / Voice and then tap on the little cloud icon next to “Siri Female” to download that voice via WiFi. Once downloaded, Siri sounds much better.
I don’t know why that’s necessary – I compared with my wife’s phone, and the full “Siri Female” language pack was downloaded already on her phone. What’s more, I’ve been connected to WiFi all day (she wasn’t!) and would have expected that some background process automatically downloads the enhanced voice. Odd.
*) I’m not too thrilled with the update in general – the clunky headers “Messages”, “Contacts”, “Mailboxes” etc. are a gigantic and completely useless waste of space – I have the iPhone 7 Plus for the larger screen, with these stupid headers it feels like a device for vision impaired people and there’s no way to turn that nonsense off…