Deckline DJ

Deckline DJ is a two-deck DJ app for the music files you own. Load a track on each deck, match their tempos with SYNC, and blend them on a mixer with EQ, a filter and a crossfader.

Each deck has a scrolling waveform with a beat grid, a whole-track overview and a platter you can scratch with your finger. The tempo fader on the outer edge of each deck goes up to plus or minus 50 percent, key lock keeps the pitch steady as you change tempo, and the key badge shifts a track up or down by semitones.

When you add a track, Deckline analyses it on your device for tempo, beat grid, musical key and loudness. Keys are shown in Camelot notation and turn green when the two decks mix well together. SYNC matches the tempo and lines up the beats, and keeps them lined up when the other deck's tempo changes.

Deckline can split any track in your library into vocals and music on your device. Turn the vocal off for an instrumental, turn the music off for an acapella, or set both levels anywhere in between. Each track is separated once, before you play it, and saved for next time. The first split downloads the separation model (15 to 33 MB). Separation uses MIT-licensed Ultimate Vocal Remover models.

Under each deck is a row of performance pads: 8 hot cues, loops of 1 to 8 beats that you can halve, double or move by beats, and a beat-synced echo and a reverb.

The mixer has three-band kill EQ, a one-knob filter, channel faders with level meters, and a crossfader with smooth, blend and scratch curves. With split output, one pair of headphones carries the main mix in one ear and the deck you are cueing in the other.

Record your mix to an AAC file and share it from the app.

Add music from the Files app, DRM-free songs from the Music app, or copy files into the Deckline DJ folder with Finder. MP3, AAC, WAV, AIFF, FLAC and ALAC files work. Two demo tracks are included so you can start mixing straight away.

Private by design: no accounts, no analytics and no advertising. Your music never leaves your device; the only download is the stem model.

Limits: Deckline plays audio files stored on your device. Songs from Apple Music, Spotify and other streaming services are protected and cannot be loaded. Stems are vocals and music (two stems) and are separated before you play rather than live. There is no MIDI controller support yet. On iPhone, Deckline runs in landscape.