Preparation: library, stems, levels, meters

What is done before a set, at home or at soundcheck, so that nothing has to be done during it. The on-stage checklist is in live on stage.

The library travels on one stick

In the Pioneer world one USB stick in any player is enough: every other player on the Pro DJ Link network sees and loads from it. DJs expect exactly that, and it is A³’s target too (decided 2026-10-29, not built yet):

  • one stick at any deck host serves the library to every deck on the network;

  • A³ Core can also serve a library from its own disk;

  • a deck loads a track whole into memory, so the network is only read at load time, never during playback.

Until then each deck host needs its own copy of the library.

Stems are made beforehand

Stem separation (drums, bass, other, vocals) without a GPU takes hours per track: a measurement in 2026-10 found demucs.cpp on a desktop CPU 6× slower than real time for htdemucs and about 25× slower for the finer htdemucs_ft. On the machine that plays the set it would compete with the audio. So stems are made on the DJ’s own computer before the gig and copied into the library, the way a rekordbox user analyses tracks at home. (A³ decision, 2026-10-26; the tool lives in its own repository.) Any text promising “it splits tracks itself” on the rig over-promises.

Prepare the track, not the moment

  • Beat grids are checked at home. A deck aligns to the beat; where the “one” is, a DJ sets by hand on the jog, as on a CDJ.

  • Tempo range: a deck’s pitch range should offer the CDJ’s steps (see CDJ-3000).

  • Key lock (Master Tempo on a CDJ, KEY on StemDeck): the high-quality time-stretch costs more CPU; a change of engine is applied only where nobody hears it — when the deck is stopped or at the next load.

Levels and meters

  • Gain staging is set at soundcheck, with the room as loud as it may ever get at the top of the trim, and set up quietly first (“start quiet”).

  • One meter behaviour everywhere (A³ decision, 2026-10-07). Every display in the booth — deck screens, desk displays, channel LEDs, the main meter — shows the same peak with the same ballistics, so two meters never disagree about one signal:

    • attack immediate;

    • release 20 dB/s;

    • peak hold 1.5 s, then falling at 20 dB/s;

    • the shared LED scale −36, −24, −18, −12, −9, −6, −3, 0 dBFS.

    That is a little livelier than IEC 60268-18 (20 dB in 1.7 s, about 12 dB/s), which is right for a booth.

  • A clip indicator must never disappear before its hold mark: give it the same 1.5 s as the peak hold.

The clock

Who is tempo master is agreed before the doors open, not discovered at the drop. See Pro DJ Link and the clock card in live on stage.

Rehearse in headphones

A drag on the sphere and a recorded take are heard by the room as they happen, so a movement is rehearsed in the headphones first. A³ decodes the cue as B-format to binaural headphones (one HRTF for everything), so a movement can be heard in the phones. Which channel setting keeps a rehearsal out of the room while it still moves in the phones is an open question in the documentation (2026-09-29: “3d down, cue on” was proposed and is to be confirmed).