A small tool for a specific annoyance.

SoundFerry routes Mac system audio through a virtual speaker instead of relying on player-specific integration. Check that the player uses the Mac system output.

The result is a Core Audio HAL plug-in — a real macOS output device — that captures whatever the system is playing in a lock-free ring buffer touched only by the render callback, runs it through a double-precision processing chain, and hands a single stream to a local AirPlay 2 engine which fans it out to every receiver you ticked.

Deliberately, the driver publishes no input stream. Most tools that capture system audio do it by opening one, which macOS treats as recording — hence the microphone prompt, and hence the virtual device showing up in every other app's list of recording sources. SoundFerry passes audio through a custom Core Audio device property. The app does not request microphone permission.

The audio chain came later and grew larger than planned, because once you are sending to real speakers in real rooms you immediately want to fix what you hear. It is now 12 parametric bands, dynamics, stereo width, a look-ahead limiter and loudness metering. CPU use depends on your Mac and processing settings.