Silence.
Volume.
Headphones.
Best practices
Adjust levels automatically when necessary — don’t adjust the overall volume.
Permit rerouting of audio when possible.
Use the system-provided volume view to let people make audio adjustments.
Choose an audio category that fits the way your app or game uses sound.
Respond to audio controls only when it makes sense.
Avoid repurposing audio controls.
Consider creating custom audio player controls only if you need to offer commands that the system doesn’t support.
Let other apps know when your app finishes playing temporary audio.
Handling interruptions
Determine how to respond to audio-session interruptions.
When an interruption ends, determine whether to resume audio playback automatically.
Platform considerations
iOS, iPadOS
Use the system’s sound services to play short sounds and vibrations.
visionOS
Prefer playing sound.
Design custom sounds for custom UI elements.
Use Spatial Audio to create an intuitive, engaging experience.
Consider defining a range of places from which your app sounds can originate.
Consider varying sounds that people could perceive as repetitive over time.
Decide whether you need to play sound that’s fixed to the wearer or tracked by the wearer.
watchOS
Use the recommended encoding values for media assets.
For the complete guidance, including worked examples and illustrations, see the canonical page: https://developer.apple.com/design/human-interface-guidelines/playing-audio