The audio engine’s optional singleton main mixer node.
- iOS 8.0+
- macOS 10.10+
- tvOS 9.0+
- watchOS 3.0+
When the property is first accessed the audio engine constructs a singleton main mixer and connects it to the
output on demand. You can then connect additional audio nodes to the mixer.
By default, the mixer's output format (sample rate and channel count) will track the format of the output node. It is possible to make the connection explicitly with a different format.