ABSeq is an A/B player for iPhone and iPad. You load two to four versions of a track, press Play, and switch between them while they play in sync. Auto Gain matches their loudness, each track shows its LUFS and true peak, and Blind Test lets you choose without knowing which file you picked. It runs on iOS and iPadOS 26 or later.

Quick start

  1. Tap the top of tile A and pick a file in the Files picker. Do the same for tile B.
  2. Switch on Auto Gain so both files play at the loudness of the quieter one.
  3. Press Play. Both tracks play in sync and loop, and you hear one at a time.
  4. Press A/B to switch, or tap a tile's letter to jump to that track.
  5. Read the LUFS and dBTP figures on each tile, and tap a readout to see what the streaming services would do to it.
  6. Open Blind Test, set the rounds and seconds per passage, and pick the version you prefer each round.

To try it without your own files, tap Try demo in the tutorial, or Load the demo song in Settings. See getting started in the help guide.

Loading files

ABSeq opens WAV, AIFF, AIFC, CAF, FLAC, MP3, M4A and AAC from the Files app, including iCloud Drive. Files open one at a time through the Files picker. If someone sent you a mix by AirDrop or Mail, save it to Files first, then load it.

ABSeq reads each file where it is and analyzes it on the device. It needs no account and doesn't upload your music. To swap a file, tap the top of a loaded tile, then Replace File.

Use + and − at the top of the display to show tracks C and D. Adding a track stops playback.

Switching between versions

All loaded tracks play from the same position and loop together. When you press A/B, ABSeq moves to the next track at the same moment in the song, so you compare the same chorus or the same snare hit, not two different parts. With three or more tracks the key reads STEP and moves to the next track in turn. Tapping a tile's letter jumps straight to that track.

Export the versions from the same start point so bar 1 in one file is bar 1 in the other. The guide on how to A/B test a mix goes through the preparation.

Auto Gain

The louder of two versions usually sounds fuller and brighter, and a difference of about 1 dB can bias the choice.

Auto Gain measures each file's integrated loudness and turns every track down to the quietest one. If A measures −9.2 LUFS and B measures −11.0 LUFS, ABSeq turns A down 1.8 dB and leaves B alone. It never turns a track up, so nothing clips. A track that is still being measured plays at its own level until its reading is ready. The guide to level matching explains why it matters, and the help guide has the details.

The readouts: LUFS, dBTP and the streaming chip

Each tile shows three things about its file.

  • LUFS is the integrated loudness of the whole file, measured to ITU-R BS.1770 (EBU R128).
  • dBTP is the true peak, the highest level between samples, measured with 4× oversampling. It turns red above −1 dBTP, the ceiling Spotify asks for.
  • The streaming chip shows how much a service would change the track's level. "Spotify −1.8 dB" means Spotify would turn it down 1.8 dB to reach −14 LUFS.

Tap the readout to see every service: Spotify, Apple Music, YouTube, Tidal, Amazon Music and Deezer. The targets ABSeq uses are −14 LUFS for Spotify, YouTube, Tidal and Amazon Music, −15 for Deezer and −16 for Apple Music. Only Spotify publishes its rules in full, so treat the others as estimates. MEASURING shows while ABSeq reads a file, and Silent means it found no loudness. See track readouts.

Blind Test

Blind Test compares tracks A and B without telling you which is which. Each round plays the same short passage from both, shuffled and labelled Version A and Version B. You hear both and pick the one you prefer.

Before you start, set Rounds (1 to 50) and Seconds per passage. Auto Gain is on by default and matches the two files by itself, and Start waits while they are still being measured. The file names appear only in the results, and ABSeq saves the results with the open session.

It is a preference test, not an ABX identification test. Picking the same file 9 times in 10 is unlikely to be chance. See the guide to blind A/B tests and the help guide.

The sequencer

The sequencer switches tracks for you on the beat, so your hands stay off the phone. Switch it on and ABSeq moves to the next track on every beat division, from 1/32 to 1/1 (a whole bar). At 120 BPM, 1/1 switches every 2 seconds.

Set the tempo by hand from 1 to 300 BPM, or pick a track letter in the sequencer's details to use the tempo ABSeq detected in that file. The order can be forward, backward or random, and random never repeats the track you are on. It only switches while playing. See the sequencer in the help guide.

The graphs

Tap the key at the top right of the display to choose a graph. Graphs show once a track is loaded. ABSeq computes each graph once, when the file loads.

Spectrum (free)

FFT shows the level across 39 bands from 25 Hz to 20 kHz. The track you hear appears as bars and the compared track as a faint line, so you can see where one has more low end or more air than the other.

LUFS, TONE and A/B difference (Pro)

  • LUFS plots short-term loudness across the whole song against a −14 LUFS line, with readouts for short-term (S), momentary (M) and integrated (I).
  • TONE shows the long-term tonal balance against a slope of about −4.5 dB per octave, typical of commercial mixes, inside a shaded range. It is a general approximation, not a genre target.
  • A/B difference shows where one track has more than the other, band by band, after loudness matching. The headline names the biggest gap, for example "B +2.1 dB @ 63 Hz".

Without Pro these three graphs show blurred, so you can see what they do first. Bands below about 125 Hz are coarse, so read small differences there with care. See graphs and visuals.

iPad and foldable iPhone

On iPad and on an unfolded foldable iPhone, a second screen sits beside or above the tracks with its own graph key. You can watch two graphs at once, such as the spectrum on one screen and the A/B difference on the other.

Lock screen and background playback

ABSeq keeps playing, and the sequencer keeps switching, when you leave the app or lock the phone. The Lock Screen and Control Center play, pause and skip to the next track, and you can drag the scrubber to seek. It works over Bluetooth, wired headphones, speakers and car audio. That makes a car test simple: load the versions, press Play, lock the phone and use the next-track control on the Lock Screen to move to the next version. Unplugging headphones stops playback, so press Play again (see troubleshooting).

Sessions

A session saves the comparison: where your files are (not copies of them), their loudness, the sequencer settings and blind test results. Save with the save key at the top of the screen and open with the folder key beside it. When you leave ABSeq it keeps your setup as Last Session, replacing the one before.

If a file was moved or renamed, ABSeq lists it before opening. Tap Locate and pick the file. The free version keeps 3 saved sessions. See sessions.

Free vs Pro

A/B switching, Auto Gain, Blind Test, the LUFS, true peak and streaming readings, the spectrum and the sequencer are free. The free version shows ads.

ABSeq Pro adds the LUFS, TONE and A/B difference graphs, unlimited saved sessions, and iCloud sync of your sessions and their audio across your own iPhones and iPads. It removes the ads, and costs $19.99 once (Lifetime) or $2.99 a month (US prices). See ABSeq Pro.

Questions

How do I A/B two songs on iPhone?

Load one file into tile A and the other into tile B from the Files app, switch on Auto Gain, and press Play. Both play in sync and loop. Press A/B to switch at the same moment in the song, or turn on the sequencer to switch on the beat.

Does ABSeq change or master my audio?

No. ABSeq only plays and measures your files. Auto Gain lowers the playback level of the louder tracks inside the app, and the files themselves stay as they are.

Can ABSeq play with the screen locked?

Yes. ABSeq keeps playing and the sequencer keeps switching with the screen locked, and the Lock Screen and Control Center play, pause and move to the next track, over Bluetooth, headphones, speakers or car audio.

What is free in ABSeq and what needs Pro?

Comparing, Auto Gain, Blind Test, the LUFS and true peak readings, the streaming chip, the spectrum and the sequencer are free. Pro adds the LUFS, TONE and A/B difference graphs, unlimited sessions and iCloud sync, for $19.99 once or $2.99 a month in the US.