An audio session is the intermediary between your app and iOS for configuring audio behavior. Upon launch, your app automatically gets a singleton audio session. You configure it to express your app’s audio intentions. For example: Will you mix your app’s sounds with those from other apps (such as the Music app), or do you intend to silence other audio? How should your app to respond to an audio interruption, such as a Clock alarm? How should your app respond when a user plugs in or unplugs a headset? Audio session configuration influences all audio activity while your app is running, except for user-interface sound effects played through the System Sounds Services API. You can query the audio session to discover hardware characteristics of the device your app is on, such as channel count and sample rate. These characteristics can vary by device and can change according to user actions while your app runs. You can explicitly activate and deactivate your audio session. For app sound to play, or for recording to work, your audio session must be active. The system can also deactivate your audio session—which it does, for example, when a phone call arrives or an alarm sounds. Such a deactivation is called an interruption. The audio session APIs provide ways to respond to and recover from interruptions.