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2. Live & File Playout Synchronisation

Aim: Synchronise TDS 2 with TDSs 3 and 4

Live & File Playout Synchronisation

Scenario

  • Two microphones and a playback device are plugged into an audio mixer
  • The playback device has a stored audio TDS 1 (for example a WAV file) which consists of Data Objects and Time Values
  • The Time Values in the audio recording exist within Time Context A which is scoped within the audio file only, with the first sample occuring at a Time Value of zero
  • The Time Values produced by the microphones relate to the time at which audio hit their transducers
  • The microphones and playback device share a timing reference (for example via PTP) and as such can produce TDSs which use the same Time Context B

Behaviour & Options

  • At the time of audio playback, a new TDS is created by the playback device (TDS 2). This contains identical Data Objects to the stored TDS 1, but the Time Values are created fresh in Time Context B to permit synchronisation with other TDSs using that Time Context.

Caveats

  • As in (1), audio mixers do not typically automatically compare Time Values at their inputs and perform buffering to synchronise them.
  • As TDS 1 is unrelated to the live signals in the system, there is little benefit in this scenario to synchronise TDS 2 with TDS 3 and 4 prior to the mix. Note however that had the stored TDS 1 also contained a video track which was processed by a separate chain this may have been more important. This will likely be the subject of a future application note.