Glossary

Plain-English definitions of the terms behind AirPlay delay.

• AirPlay: Apple's wireless protocol for sending audio and video between devices, and how a Mac uses it for system sound.
• AirPlayXPCHelper: The root process in macOS that runs AirPlay audio, reads audioLatencyMs and builds the audio engine.
• Audio latency: The delay between a sound being produced and being heard, and the parts that add up to it over AirPlay.
• Buffer and jitter: Why audio streams keep a buffer, and how Wi-Fi jitter decides how small it can safely be.
• Keep-alive (AirPlay): Playing inaudible noise so AirPlay doesn't suspend the stream during silence and renegotiate it, about 370 ms, when sound resumes.
• Privileged helper: A small background program that runs with administrator rights on behalf of an app, after you approve it.
• SMAppService: Apple's API for registering login items, agents and daemons that the user approves in System Settings.
• arrivalToRenderLatencyMs: The value an AirPlay speaker reports for how long it needs between receiving audio and playing it.
• audioLatencyMs: The undocumented macOS preference that sets AirPlay's system audio buffer in milliseconds.
• dBFS: Decibels relative to full scale: the unit for digital audio levels, and why −78 dBFS is inaudible in practice.