Open-source per-app audio on Mac: the honest tradeoffs

Open-source per-app audio on Mac is real and genuinely free. Background Music gives every app its own volume slider (GPLv2), BlackHole routes audio between apps (GPL-3.0), and eqMac's older code is open. The honest tradeoff is that you pay in setup and upkeep instead of money: you install a virtual audio device, switch your default output, and lean on volunteer-run projects that can lag new macOS releases — with no support line when something breaks. For a Mac you keep for years, that's often a fair deal. For a mix you ride twenty times a day, the time it costs can outweigh the price it saves.

There's a real open-source audio scene on macOS, and it exists for a good reason: Apple never shipped a per-app volume mixer or per-app output routing, so the community built the missing pieces. If you value free, inspectable, no-telemetry software — and you're willing to do a little assembly — you can cover a lot of this ground without spending anything. This guide lays out what each open-source tool actually does, where each one stops, and the tradeoffs nobody puts on the download page.

What "open-source per-app audio" actually includes

Three projects come up most, and they do not do the same job. It's worth separating them before you install anything, because "open source" and "free" don't mean the same thing from one to the next.

• Background Music — a free, open-source menu-bar app (GPLv2) that sets a per-app volume for every running application, auto-pauses your music when other audio plays, and can record system audio. This is the one true open-source per-app volume app.
• BlackHole — a free, open-source virtual audio driver (GPL-3.0) that passes audio from one app to another with no added latency. It's a routing building block, not a volume app: on its own it has no sliders and no per-app UI.
• eqMac — an EQ-first app whose older codebase was released under Apache-2.0. Its system equalizer is free, but the per-app Volume Mixer is a paid Pro feature, and the current app isn't fully open. So "open-source per-app volume via eqMac" doesn't really hold up.

Background Music: the real open-source per-app mixer

If you want free, open, per-app volume and nothing else, Background Music is the answer and it's a good one. It installs a virtual output device, makes itself your Mac's default output, and then shows a tidy menu-bar list with a slider for each app that's making sound. Drag Spotify down, leave a call up, mute a browser. It's the closest thing the open-source world has to the Windows Volume Mixer, and it costs nothing.

The honest caveats are about upkeep and reach, not honesty of purpose. It's a volunteer project, and its pace has been uneven — new macOS releases have historically needed community patches before everything settles. Because it works by routing all audio through its own virtual device, you're handing one more layer your entire sound path; most people never notice, but when something misbehaves there's no support desk, only GitHub issues. And there's no keyboard control and no per-app output routing — it's a volume mixer, reached with the mouse from the menu bar.

BlackHole: a routing building block, not a mixer

BlackHole is excellent at exactly one thing: it's a virtual cable. It creates loopback devices (2, 16, 64 channels and more) so one app's output can become another app's input with zero added latency. Streamers, producers, and anyone capturing system audio rely on it, and it's free and open under GPL-3.0.

What it is not is a per-app volume app. To do anything useful you assemble the pieces yourself in Audio MIDI Setup — building an aggregate or multi-output device, pointing apps at BlackHole, and wiring the monitoring path back to your speakers. There are no sliders and no "set this app to 30%." It's powerful and free, but it's parts, not a product. If DIY routing is your actual goal, we go deeper in BlackHole vs a per-app routing app.

eqMac: open-source EQ, paid per-app volume

eqMac deserves a fair hearing because its equalizer is genuinely strong and free — a system-wide EQ with AutoEQ headphone correction profiles, and its older codebase was open under Apache-2.0. If your laptop speakers sound thin, nothing else in this category fixes the sound for free the way eqMac does.

But the thing this guide is about — per-app volume — sits behind eqMac Pro, which is a subscription (around $3 per month or roughly $40 for a lifetime license). So if you're reaching for eqMac specifically to get free, open-source per-app volume, that's the one feature that isn't free and isn't part of the open code. It's a fine EQ; it's not an open per-app mixer. Our full breakdown is in eqMac vs Fader.

The tradeoffs, side by side

Here's the honest ledger. "Free" is accurate for the software; the columns to watch are setup and upkeep, which is where open-source audio spends your time instead of your money.

When open source is the right call — and when it isn't

Choose open source when the things open source is best at are the things you care about. If you want a free, auditable, no-telemetry tool, don't mind installing a virtual device, and are comfortable reading a GitHub issue when a macOS update stirs things up, Background Music is a legitimately good per-app mixer and BlackHole is the standard for DIY routing. You'd be in good company and you'd spend nothing.

Reconsider when speed and reliability are the point. Open-source audio tends to cost you in three places: a setup that reroutes your whole sound path through a virtual device, a maintenance model that depends on volunteers keeping up with Apple, and the absence of a mouse-free way to ride levels. If you adjust your mix all day — calls, music, a stream — those add up fast. That's the honest case where paying a little buys back a lot of friction.

Where Fader fits (and where it doesn't)

Fader isn't open source, and it would be dishonest to pretend otherwise — if a modifiable, audited codebase is your top priority, Background Music is the pick, full stop. Fader's trade is the other direction: it's a paid app ($19.99 one-time, not a subscription, with a 3-day trial) built for people who want the control to be instant and the setup to be nothing.

The practical differences: Fader uses the Core Audio process-tap API that shipped in macOS 14.4, so there's no virtual driver to install and no default-output swap — it taps each app directly. It's App Store sandboxed with no account and no telemetry. And it's keyboard-first: hit a toggle hotkey and your keys become faders, so you ride app levels without reaching for the menu bar. It also does per-app output routing, which the free mixers above don't. You're paying for maintained, no-setup speed and a support address — not for a feature the open-source world can't match on paper. If you're weighing the free side specifically, see free vs paid per-app volume apps, or the direct Background Music vs Fader comparison.

Bottom line

Open-source per-app audio on Mac is real, and some of it is excellent: Background Music is a free, open, capable per-app volume mixer, and BlackHole is the free routing backbone half the Mac audio world runs on. The honest tradeoff is that you pay in setup and upkeep, not dollars — a virtual device in your sound path, volunteer-paced maintenance, no support line, and no keyboard speed. If that's an acceptable trade, go open and spend nothing. If what you actually want is to change any app's level in a keystroke with nothing to install and someone to email when it breaks, that's the gap a paid app like Fader is built to close.