What is IAB sound?

[Carsten Kurz]

And I still think it's a bad idea ISDCF voted against the fallback option, as we have seen ATMOS dropping out quite often in the past.

Although it seems nobody follows that recommendation, I have never seen an ATMOS/IAB composition without a backup track present in main sound.

[Ryan Gallagher]

Note that the immersive sound bed tracks are in the IAB bitstream, not in the 16 channel main sound. They are packets of data for each editable unit (typically 1/24 second) and include a loudspeaker destination instead of immersive parameters (like XYZ location). There are separate packets for sound fragments that are pointed to by bed or object packets.

Many DCPs include a 5.1 or 7.1 "backup track" in main sound. SMPTE has an RP that recommends against this since people may THINK they are playing IAB (or Atmos) when they are actually just playing 5.1. I think Dolby typically includes the main sound as a backup in the same way digital sound on film could fall back to analog sound.

Interesting nuance on how that was recommended, so not intended as backwards compatible to older processors, but most DCP authors are creating that backup option anyway in the standard 16 channel information as Carsten says.

Good to know, especially when festival tech-check or screening keys have an issue on a 5.1/7.1 version, but for some reason they provided an ATMOS/IAB key. I'm gonna be more tempted to ingest the ATMOS versions now rather than ignore them in festival mode.

[Carsten Kurz]

I have no idea how other servers deal with an ATMOS VF and KDM if no ATMOS system is installed. Our Sony software is 'ATMOS' aware, in that there is an ATMOS license option for the Sony systems, but it is not active on our server.