let utterance = AVSpeechUtterance(string: "Hello world")

// Method 1: Directly by identifier
utterance.voice = AVSpeechSynthesisVoice(identifier: "com.apple.ttsbundle.Karen-compact")

// Method 2: By langauge code
// What will be chosen? Compact one or Enhanced one?
utterance.voice = AVSpeechSynthesisVoice(language: "en-AU")