Configure your dictation engine, microphone, and custom vocabulary in Settings › This Mac › Voice.
Three recognition engines are available: Apple (uses macOS built-in speech), SenseVoice (optimised for Chinese and fast languages), and Paraformer (a local model that works without an internet connection). Switch engines in Settings › This Mac › Voice › Engine.
You can also choose which microphone to use if you have more than one connected, and add a custom vocabulary list for technical terms, product names, or people's names that the engine might misrecognise.
Where: Mac app › Settings › This Mac › Voice.
Good to know: all three engines run locally on your Mac — your audio is not sent to a cloud speech service. Changing the engine takes effect immediately. Related: Use voice dictation in a chat.