Taperlark / Submix
macOS ships with exactly one volume control that matters system wide, and it moves every app's audio at once. Turning down a notification sound also turns down the call you are on, muting a browser tab means digging through that browser's own settings if it has any, and routing one app's audio to a different output device usually means changing the whole system's output first. For anyone running more than a couple of audio sources at once, that single slider is a constant source of small, avoidable interruptions.
Submix gives every running app its own volume, mute, and output routing, so a notification does not have to compete with a meeting and a game does not have to share an output device with the calendar reminders. These notes track how that per-app audio graph is built on top of Apple's own audio session model, the tradeoffs behind specific controls, and what changes as new macOS releases adjust how apps are allowed to expose their audio streams.
Background Music failing to launch after a macOS update, sliders that do nothing, or sound gone quiet after uninstalling: which failures have fixes, which are the design, and what to run instead, with every claim attributed to the project's own README and issue tracker.
macOS has no per app volume slider, but the answer does not end there. The app's own controls, Safari's tab mute and the alert slider cover some cases, and a per app mixer covers the rest: one volume row per app, so you can lower or mute any of them alone.
Crackling, pops and dropouts after a Mac update are a documented chapter of macOS 26's launch. Here is the dated record from Apple's support communities and audio vendors, the workarounds that circulated, which ones make mechanical sense, and what a per app mixer honestly cannot fix.
Five real SoundSource alternatives, compared honestly: the free and open source Background Music and FineTune, the paid SoundDial and Submix, the freemium BetterAudio, and a straight answer to whether SoundSource itself is worth it.
macOS ships no volume mixer: nothing in System Settings can turn one app down on its own. Here is why Core Audio never had one, what Apple changed in macOS 14.2, and the four real ways to get a per app volume mixer on a Mac today, two of them free.
Submix gives every running app its own volume, mute, and live meter through a Core Audio process tap, with no driver and no admin password. Here is the mechanism behind the mixer, what it does not do yet, and who it will not fit.
Submix installs no audio driver, kernel extension, or system extension. It asks for one macOS permission, and this is what happens if giving your audio back does not go as planned.
A Multi-Output Device sends the same audio to every output at once. Sending different audio to different destinations, like music to speakers and a call to AirPods, needs a per-app audio tap instead, the API macOS added in version 14.2.