How it works
Stream AB mutes your track, drives whatever is already playing on your computer, and measures both. It never routes, records or re-encodes the reference.
The switch
Free versionPut 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.
One button, two sources
Click to switch. The side you are hearing is lit, and the reference starts and stops with it.
A/B is also a real plugin parameter, so you can automate it or map it to a MIDI controller or keybind - it keeps working with the window closed.
Gain matching
The gain trim moves your signal 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.
Manual trim
Free versionDrag the slider, or type a value, until the two sound equally loud.
Auto gain match
Full versionOne press listens to both sides and sets the trim for you, ending on your mix.
Auto gain match switches to the reference, listens to both sides, switches back and slides the gain to match - usually six to fifteen seconds. It matches what you are hearing, not what each track was mastered to: if the reference plays 11 dB quieter, your mix comes down 11 dB, because the point is a fair comparison of tone, not a volume test.
It measures the passage that plays while it listens, so a verse and a chorus give different answers - which is what you want when A/B-ing a section. If the level never settles, it says “Approximate” and you trim the rest by ear. Clicking anywhere else cancels it.
Loudness and tone
Full versionTwo panels measure your mix and the reference the same way, side by side. Your mix is measured before the gain trim and codec preview, so moving the slider does not move the reading.
Loudness analysis
Integrated and short-term LUFS, momentary and true-peak meters and loudness range, for A and B. Pause or reset either side on its own.
Tonal balance
Your mix and the reference on one graph, as a fine curve or four broad bands. Hover to read the frequency; Reset starts both averages again.
Loudness is measured to ITU-R BS.1770, the standard streaming services use. 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, measures only while B is audible, and quits with your DAW. B’s readings calibrate to each track’s loudest peak, so your streaming app’s volume does not skew them. Nothing is recorded - it produces numbers, and nothing leaves your machine.
macOS
System-audio capture lives behind the Screen Recording permission - that is just where Apple keeps it. It is asked for once, when you activate your licence. Needs macOS 13 or later. See the support page.
Windows
Audio loopback is built into Windows. No permission, no prompt, nothing to install.
Search and saved references
Full versionType a track, click it, it plays - without leaving your DAW. The plugin asks the service’s app (or your browser, for YouTube) to play the song and keeps it behind your DAW while it does. Picking a track pauses whatever else was playing first.
Four services
Spotify, Apple Music, YouTube and TIDAL. Click the service logo to switch; choose which ones appear in Settings.
Saved references
Heart a result, or press Save while a track plays. The heart button opens your list; pick one to cue it again.
Spotify needs no login and no Premium. Apple Music and TIDAL play through your own account in their apps. Tracks you have played also stay as a strip of recent references, which survives closing the plugin.
Looping and transport
Full versionSection loop
Drag across the scrub bar to loop a section, or right-click the section loop to type the start and end.
Full-song loop
Repeats the whole track, so a reference keeps playing while you work.
Loop points belong to the track - change track and they clear. The scrub bar jumps anywhere in the reference, and the skip buttons move between tracks, all from inside the plugin.
Streaming codec preview
Full versionHear it after compression
The ear button plays your mix through a streaming-quality codec, chosen from a dropdown, so you hear what compression does to it before release.
On macOS the presets are named for the services and quality settings they approximate - Spotify, Apple Music and YouTube Music. On Windows they are named for the codec itself: AAC, Opus and Vorbis at a range of bitrates.
It previews codec quality, not a service’s loudness. While it is on it adds about a quarter of a second of latency, which your DAW compensates for. Turn it off before you export, or the export will be encoded too.
What depends on your OS
Switching and the transport work the same everywhere. What varies is the track display - title, artwork, scrub bar, loop points.
Windows
A documented media API that browsers report to, so every source shows full information in every DAW.
macOS
Apple 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 to control Spotify and Music. If a future update closes the route, the display narrows to Spotify and Apple Music; switching is untouched. Details.
VST / AU / AAX · macOS and Windows · 2 machines per licence