Stems

When the deliverables ask for stems, deliver one file per part of the mix that adds up exactly to the mix.

• The parts: dialogue, voiceover, music (the chosen option and its stems), effects (the designed effects and the shots' own sound, which carries its own foley), ambience, and other for any other role. A part the film doesn't use makes no file.

• The format: 48 kHz, 24-bit stereo WAV, named after the film master.

• Never normalised on their own. Every stem carries the mix's own gains, ducking and final gain, so the stems added together equal the mix. A stem never goes through a loudness correction, which would break the sum.

• Prove the sum before you deliver: sum all the stems with the mix, its polarity inverted, and measure what is left. The residual's RMS level must sit at least 60 dB under the mix's (steps below).

• If it won't sum, usually because a limiter or dynamic loudness changed the mix's gain, lower the loudest peak in the mix (usually one effect or hit) and render again. Failing that, export the stems from your Premiere mix by soloing each group of tracks in turn.

Stems are delivered flat, under the version table's names.

Do it yourself

Run the null check: prove the stems sum to the mix (Premiere, Audition or ffmpeg)

1. Lay all the stems in a new sequence with the mix beside them, its polarity inverted (Premiere's Invert effect).

2. Export what is left: the residual.

3. Measure it with Audition's Amplitude Statistics, or with ffmpeg, whose Overall section gives the RMS level:

ffmpeg -i residual.wav -af astats -f null -

1. Measure the mix the same way. The residual's RMS level must sit at least 60 dB under the mix's.

Sources

• From standard post-production delivery practice.