4DJ is an iPhone and iPad DJ app described with two decks, a mixer, effects, track analysis and mix recording. The official US listing presents its detailed description in Italian. This first look translates those stated capabilities without claiming a practical controller, audio-routing or performance test.
The audience is a DJ or solo performer who wants to understand what can happen on the device and what depends on an attached console. The app is described as usable with or without a console, but a feature list does not establish that every phone, audio connection and controller combination behaves identically. A rehearsal with the actual setup remains an essential evaluation step.
Based on official store information. We have not tested this app hands-on.
What it does
StemX separates a track into drums, bass, vocals and other material directly on the device, with an acapella or instrumental control. That is a specific processing claim, not a guarantee that every recording separates cleanly. The source does not establish measured sound quality, processing time or rights to redistribute extracted material.
SmartSync and Key Morphing align tempo and key according to the developer. Detailed waveforms accompany automatic BPM, beatgrid and key detection. Eight hotcues, looping, beatjump and SLIP provide performance controls. These tools can help organize a transition, but the accuracy of automatic analysis and the musical result still need listening and review.
The mixer includes gain, three-band EQ, filter, crossfader and headphone preview. Two FX units offer nineteen effects, with Mixer FX on each channel's filter. The iPad uses a fuller screen arrangement, while iPhone has dedicated deck, mixer and browser views. Those layouts are different ways to expose the same broad tasks, not evidence that every gesture or hardware control maps identically.
Before you install
Begin with music you have permission to use and a short transition that exposes the expected tasks. Inspect the analyzed beatgrid and cue points before trusting automatic alignment. Listen to the result rather than treating matching numbers as proof that two tracks form a convincing or technically clean mix. We have not measured synchronization, key changes or the behavior of unusual rhythms.
The library includes playlists, smart playlists, history and track analysis. Use those structures to distinguish prepared material from an unreviewed file. The source does not identify every supported import route, streaming service or audio format. Having a music library feature does not establish integration with a particular subscription catalog or a license to perform it publicly.
More than one hundred ten USB MIDI DJ consoles are described as recognized when connected, including their lights. Other MIDI consoles can be configured with a guided assistant, according to the developer. The advertised quick setup should not become a promise that every unsupported controller works without adjustment. Check the actual model, adapter, power requirements and control mapping before a paid event.
Multi-Route is described as sending the master to a speaker while headphones use the console. That is a specific routing arrangement, not evidence that a phone alone supplies every separate audio output. Verify the actual cue and master destinations at a safe listening level before using the setup with an audience. Recording a mix is also a separate action to inspect rather than assuming every performance is automatically saved.
Price and access
The official US App Store offer is a free download. The description does not establish a current paid-tier schedule, in-app purchase price or a complete boundary between free and paid capabilities. Check the current store and app access information before planning a performance around a particular function.
Hardware, adapters and music rights remain separate from installation. The developer says 4DJ collects no data and keeps music on the device. Those are source claims, not an independent privacy audit or a blanket statement that every external asset or connected service has no cost. Interface languages named in the listing are Italian, English, French, German and Spanish.
Our take
4DJ's strongest documented proposition is combining preparation and live controls with on-device stem separation. The described library, analysis, decks and routing options form a coherent performance workflow rather than a single novelty effect. The practical value depends on the actual music, device and control arrangement fitting together.
The qualified take is to rehearse the complete route from loading tracks to cueing, mixing and checking a recording. Inspect StemX and automatic alignment as tools whose results must be heard, and confirm hardware routing separately. The listing supports a substantial DJ feature set, but it cannot establish flawless separation, universal console support or readiness for a particular paid performance.
For a solo DJ preparing a small event, the most useful rehearsal is the full signal path. Load a track, check the analysis, set a cue, hear the headphone preview, move the crossfader and inspect the recorded result. Each step tests a different part of the proposed workflow. A successful connection to a console does not by itself establish that the audience and headphones receive the intended signals or that a recorded mix contains the expected performance.
Sources
App icon from the official store listing.
