According to the Microsoft Learn module “Explore speech capabilities of Azure AI” and the AI-900 Official Study Guide, speech synthesis (also known as text-to-speech) is the process of converting written text into spoken audio output. Azure’s Speech service provides this functionality, allowing applications to produce human-like voices dynamically.

Let’s evaluate each scenario:

A. Automated voice that reads back a credit card number entered into a telephone keypad → YesThis is a classic text-to-speech (TTS) use case. The application converts numeric or textual input (such as a credit card number) into audio output that the caller hears. Azure Speech service can handle such voice responses in automated phone systems or IVR (Interactive Voice Response) setups.

B. Generating live captions for a news broadcast → NoThis is a speech-to-text scenario (speech recognition), not speech synthesis. It involves converting audio speech into written text.

C. Extracting key phrases from an audio recording of a meeting → NoThis involves speech-to-text followed by text analytics, not speech synthesis.

D. An AI character in a computer game that speaks audibly to a player → YesThis is a direct example of speech synthesis, where the character’s dialog text is converted into realistic spoken output for immersive interaction.

Therefore, based on Microsoft’s AI-900 curriculum, speech synthesis is used in applications that convert text into audible speech, such as automated voice systems or interactive digital characters.