Combining multiple audio signals onto single channel or carrier — broadcast and post workflows. Reverse process is demultiplexing for signal separation.
Packing multiple audio signals simultaneously onto a single physical channel or data line—that's the core task of multiplexing. In everyday broadcast, you need this to transmit music, speech, effects, and timecode over a single line instead of running four separate cables. On set, this works through temporal or frequency-based interleaving: you send signal A in time slot 1, signal B in slot 2, or you assign both to different frequencies. This has long been standard at the mixer—your multichannel interface internally multiplexes eight or sixteen tracks onto USB or Dante so they can be transported at all.
In post-production, multiplexing becomes a central efficiency issue. When you post-process live recordings or multi-camera documentaries, you combine audio and timecode onto one track to minimize sync problems. Professional recorders like the Sound Devices MixPre use multiplexing to already store backup tracks in compressed form during recording—in case the main track clips or a cable fails. This saves your take. In digital broadcasting (DAB+, DVB), transmitters multiplex dozens of programs into one data stream; your FM stereo audio signal sits on carrier frequencies that are also multiplexed.
Practical on Set: Ensure your de-multiplexing works cleanly. If you send four channels over a Dante line and only receive three at the other end, there's usually a multiplexing error—router settings, incorrect Dante flows, or the bandwidth is saturated. Test before shooting: send all channels, separate them again, and check if levels and phase relationships are preserved.
Relevant in Editing: Some NLEs (Avid, Premiere) automatically multiplex during export—you provide mono stems, and the system combines them for backup files. Check the output settings, otherwise you'll lose channels or get incorrect assignments. Multiplexing is invisible when it works; problematic when it doesn't.