How it works

Put Stream AB on your master. A is your mix - audio passes through with a gain trim. B mutes your track and sends a play command to whatever owns the system’s media session - Spotify, a browser tab, Apple Music, TIDAL. Back to A, and it pauses.

Both happen together, so you never hear both or neither. And because A/B is a real plugin parameter, you can automate it or map it to a MIDI controller or keybind - it keeps working with the window closed.

The gain trim moves your signal, -24 to +24 dB, so your mix sits level with the reference. It never touches side B. It is a plugin parameter like any other: saved with the project, automatable, mappable.

Auto gain match (full version) does it for you. Press it: the plugin switches to the reference, listens to both sides at once, switches back and slides the gain to match - about eight seconds, ending on your mix.

It matches what you are hearing, not what each track was mastered to. If Spotify plays the reference 11 dB quieter, your mix comes down 11 dB - the point is a fair comparison of tone, not a volume test. It measures a 3-second window, so matching against a verse gives a different answer than a chorus, which is what you want when A/B-ing a section. Clicking anywhere else cancels it.

Each band opens a panel with a LUFS reading and a spectrum for that side, and both panels always draw both sides - the one you are looking at solid, the other as a dashed ghost. One picture, not two.

Loudness is measured to ITU-R BS.1770, the standard streaming services use. Click the readout to cycle momentary, short term and integrated.

The spectrum has two views - a fine curve, and four broad bands. Hover to name the frequency under the cursor; the reset button starts the average again. Your mix is measured before the gain trim, so moving the slider does not move the reading.

Your mix is easy to measure - it is passing through the plugin. The reference is playing in another app, so a small helper installed with the plugin listens to what your computer is playing and measures it with the same code. It has no window, runs only while B is audible, and quits with your DAW. Nothing is recorded - it produces a loudness figure and a set of band levels, and nothing leaves your machine.

Type a track, click it, it plays - without leaving your DAW. No Spotify login and no Premium: the plugin just asks the Spotify desktop app to play the track, starting it if needed. Picking a track pauses whatever else was playing first.

Tracks you have played stay as a strip of recent references, and the list survives closing the plugin.

Drag across the scrub bar to set a loop, or type the In and Out times directly. The reference stays inside it. Loop points belong to the track - change track and they clear.

Switching and the transport work the same everywhere. What varies is the track display - title, artwork, scrub bar, loop points.

Windows has a documented media API that browsers report to, so every source shows full information in every DAW.

macOS restricted now-playing information in 15.4. Stream AB works around it - today, full information for every source in every DAW tested - via a one-time permission prompt to control Spotify and Music. If a future macOS update closes the route, the display narrows to Spotify and Apple Music; the switching is untouched. Details on the support page.