Topics covered in this article:
- QC of a Dolby Atmos master file
- QC of an exported Dolby Atmos master file format
- QC of Dolby Atmos master files with third-party tools
- Master file QC listening environment
- QC of channel-based deliverables
- QC of the MP4 export with professional and consumer tools
- QC criteria for Dolby Atmos
QC of a Dolby Atmos Master File
QC can begin as soon as the master file is finalized following a recording.
QC of the master .atmos file set can be performed from the Renderer either as an audio-only playback or synchronized to a proxy or reference video played back from the DAW.
QC of an Exported Dolby Atmos Master File Format
If the deliverable is an ADM BWF or IMF IAB, export the ADM BWF or IMF IAB per the delivery specs (with or without pre-/post-roll as required) and open the exported file for the QC pass. While export to ADM BWF is non-destructive, it is still best practice to QC the final deliverable. Export to IMF IAB quantizes the metadata, so it is important to QC the exported file.
There are third-party IMF mastering applications on the market that can import Dolby Atmos master files. These can be used to QC the Dolby Atmos master against reference video, as well as to author and QC the complete IMF package. These include Colorfront - Transkoder, Rohde & Schwarz - Clipster, Black Magic Designs – Resolve, and MTI Film - Cortex
Master File QC Listening Environment
Audio QC should be performed in a 7.1.4 listening environment. If performed in a dedicated QC environment, professional monitoring/monitor control should be used in a room with sufficient isolation and Noise Criterion NC) rating. This does not need to match the mix environment.
QC of Channel-Based Deliverables
All channel-based deliverables must be QC’ed. This includes full mixes, M&E, and stems as required. This can be done in the DAW, either using live re-renders or by exporting offline re-renders from the Renderer and importing into the DAW.
Remember that dynamics processing may need to be applied in the DAW to achieve True Peak limits. In this case the results should be bounced to disk and QC’ed as the final deliverable of the channel-based assets.
Third-party playback and automated QC platforms can also be deployed, as per the delivery spec.
QC of the MP4 Export with Professional and Consumer Tools
The Renderer allows for the export of an MP4 file with the Dolby Atmos master file encoded as Dolby Digital Plus JOC with black 720p video. Film and Music encoding modes can be used at appropriate for the content. Film encoding mode allows user selectable encoding at 448kbps or 768kbps to provide parity with common streaming bitrates.
It is also possible to demux the encoded Dolby Digital Plus stream (.ec3) and mux with program video encoded with the .h264 or .h265 codecs.
Instructions for doing so using free command line tools or using Amazon AWS Media Convert are available on the Dolby Atmos Post and Music Production Knowledge Base.
QC of the MP4 (with black or replacement video) is possible via several methods including:
Sideloaded on a USB drive and played back via a Blu-Ray player set to audio passthrough and connected via HDMI to an AVR enabled with Dolby Atmos or soundbar with Dolby Atmos.
Options for streaming playback include (but are not limited to):
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- Playback via the Plex server application from a Mac or Windows computer to the Plex Player application on an AppleTV4k connected via HDMI to an AVR enabled with Dolby Atmos or soundbar with Dolby Atmos.
- Streamed from AWS storage packaged as Apple HLS via a Safari browser and “pushed” to an AppleTV4k using Airplay connected via HDMI to an AVR enabled with Dolby Atmos or soundbar with Dolby Atmos.
- Streamed from a Mac or Windows computer configured as an HTTP server with playback of HLS packaged .m3u8 via a Safari browser “pushed” to an AppleTV4k using Airplay or MPEG-Dash packaged .mpd from the VLC application to a Google Chromecast Ultra4k. Either connected via HDMI to an AVR enabled with Dolby Atmos or soundbar with Dolby Atmos.
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While the first method is straightforward, the others require additional knowledge, effort, and configuration.
Playback on consumer devices allows QC of the mix on a variety of possible listening configurations, including soundbars, a variety of discrete speaker configurations, upward-firing speakers, and Dolby Atmos virtualization with tablets and phones.
QC of the MP4 can also be done on professional applications such as the Dolby Reference Player, GrayMeta Iris QC platform, with file-based analysis using MediaInfo, and other third-party QC applications.
QC Criteria for Dolby Atmos
QC criteria for Dolby Atmos mixes is a superset of criteria used for channel-based assets. Basic audio QC criteria apply such as:
Objective criteria:
- File duration
- Sample rate (channel-based assets)
- Bit depth (channel-based assets)
- Conformance with loudness specification (LKFS/LUFS)
- True peak levels (channel-based assets only)
- Clipping/distortion
- Dropouts
- Hiss
- Crackle
- Ticks/pops
Subjective criteria:
- Dialog intelligibility monitored in 7.1.4 (and lower) speaker layouts
- Missing effects
- Synchronization with picture for lip sync and effects
Subjective criteria unique to QC for Dolby Atmos:
- Object placement in relation to onscreen action
Reporting of QC issues should be done in conformance with the customer requirements re:verbiage, severity, format, etc.
Note that third-party professional QC providers are also sanctioned by some of the leading streaming services.
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