Audio post production can be very rewarding. It involves creative processes which allow us to enhance the storytelling in TV shows and movies. The direction you choose for the sound and the way in which the sound design, music and dialogue are crafted can have a huge impact on the audience’s perception of the production and the narrative as a whole. Alongside the creative aspects though, there are plenty of technical points to bear in mind as well. These need to be considered from the outset of the project in order to guarantee as smooth a production as possible and to avoid unexpected issues and hurdles further down the line. Let’s consider some of the common points.

AAF

One of the very first stages in the audio post production process is receiving and importing the audio from the video editor. Audio is typically received in the form of an AAF. This stands for Advanced Authoring Format and it’s a method by which timeline audio and accompanying metadata can be transferred between video editing software and DAWs. When it works it’s great but there’s a lot that can go wrong with AAF transfers as we highlighted in the article ‘AAF and OMFs - Post expert panel on the good, the bad and the ugly’ back in 2020.

It’s easy to get an AAF export wrong, which can mean missing files or discrepancies with frame rates, sample rates or start times. It’s worth creating a guide document to send to video editors to assist them in the process of creating AAFs. This make things easier for them and reduces the likelihood of you encountering any problems when importing the audio.

Complicated Specs

Making things sound nice is one thing, but in audio post we also have to contend with a variety of specifications, especially those relating to loudness. Years ago, TV loudness was based around a peak level. We used peak program meters (PPM) and mixed shows so that their peak level didn’t exceed PPM6. This started to really become a problem when digital peak limiters made it possible to maintain the same peak level but increase the average, making the content sound louder. The specification did not prevent this and so commercials and some program content were pushed into the limiter as the loudness war started to creep into broadcasting.

The solution we eventually moved to was a system which represents how the human ear perceives loudness. This system is the BS1770 standard and from this measurement system we have a variety of different specs and target levels. Which one you work to depends on where the content you’re mixing is going to be shown. Broadcast content in Europe is mixed to the EBU R128 spec, in the USA it’s ATSC A/85 and in Australia it’s Op-59. Other countries around the world have their own specs and each set of specifications including a target integrated (average) loudness, a maximum true peak level and a maximum allowable loudness range (LRA). Some specs indicate loudness in LUFS and some use LKFS. If you’re confused about loudness, you’re not alone. Fortunately, there’s a great article on loudness from Mike Thornton which explains everything you’re likely to need to know about it.

What’s clear is that we really need to be aware of loudness and have a good understanding of it in order to successfully create compliant mixes. Aside from TV broadcast, streaming platforms such as Netflix and Amazon Prime have their own loudness requirements and cinema trailers and commercials work on an entirely different system altogether which is based on another type of metering called Loudness Equivalent, M weighted (LeqM). Thankfully, Mike Thornton has once again put together a comprehensive article on this which covers how and why the specs exist and how to measure it.

Stems And Deliverables

For some content the main mix might be all that’s required. As long as it’s technically solid and it meets the required loudness spec, a single mix can be the only deliverable needed. This is the case for some TV content and for a lot of corporate video audio. More often than not though, there’s a list of deliverables which can go way beyond just the main mix. For a feature film mixed in 7.1, the deliverables can include some or all of the following.

• 7.1 theatrical printmaster

• 5.1 theatrical printmaster

• 2.0 stereo theatrical printmaster

• Music and effects mixes (fully filled) in 7.1, 5.1 and stereo

• 5.1 TV mix

• 5.1 TV M&E mix

• Dialogue, music and effects stems, 7.1, 5.1 and stereo, sometimes in both theatrical and TV versions.

This list is just an example of some of the most common requirements. Sometimes you will be asked to provide even more than this. Working in Dolby Atmos further complicates the required deliverables too.

It’s a very good idea to consider the required deliverables right from the very beginning of the project as it will dictate how you need to set your session up and the workflow you need to employ in order to actually get it right. There’s potential to be caught out with various things regarding deliverables from not creating a fully filled foley mix to routing tracks in your session in such a way that’s is difficult or impossible further down the line to actually separate the elements you need to, and to create suitable down mixes. This is why templates are a good idea. Once you’ve found or created a session template which works for a given set of deliverables, stick with it and use it for future projects. It makes no sense to be creating routing from scratch on every project.

Down Mixing While Keeping Loudness Readings

Now that we’ve considered loudness specs and deliverables, there’s something else which needs to be mentioned: downmixing. Downmixing is the process of creating a version of a mix with fewer channels. For example, from a 7.1 mix you might need to create a 5.1 version and a stereo one. At this point the loudness can and will be affected in the process. What’s more, dialogue clarity can be affected and delay artefacts can occur. A proper downmix cannot be created in a hurry or as an afterthought. Due care needs to be given to the sound and to the measured loudness. Sometimes you’ll want to maintain the loudness and dynamic range in the stereo downmix. When creating a TV version from a theatrical mix you will need to work to a different integrated loudness spec and probably reduce the dynamic range with careful use of compression too. Pro Tools includes a basic downmixer plug-in which can be fine for some projects. Where more comprehensive control of the downmix is required though, more specialised tools such as Halo Downmix from Nugen Audio are required.

Quality Control

Quality Control or QC involves a thorough check of the final exported version of a TV show or movie. It’s a critical part of the production process because the master you provide will be the basis for all subsequent formats and versions of the production. It may be used to create a DCP file for cinema distribution, versions for online streaming or perhaps blu ray versions. Since these will be derived from the master you provide, it’s important that any technical issues present on your master are detected and corrected. The QC process is usually carried out by a third party and involves scrutinising the master very carefully, looking for any issues with both the audio and video. On the audio side this includes measuring program loudness and ensuring it’s compliant with required specs, checking for sync issues, drop outs, glitches, processing artefacts and noise. 

The outcome of the QC process is a written report which details any detected issues. These issues will be given a rating of 1-3. Issues with a 1 rating will be slight and may not need addressing. Issues given a rating of 2 may be picked up by viewers and are advisable to address and correct. Anything with a rating of 3 is considered serious enough that it would adversely affect the viewing experience and would result in the content being rejected if not corrected. 

Although quality control is crucial, it can also be annoying, not only because of the additional time it takes to correct the issues identified in the report but also because sometimes things can be flagged which were either intentional or which you may regard not to be an issue. Some items can be disputed and downgraded in severity if it can be successfully be argued that it was done as a deliberate creative choice but most of the issues rated as 3 must be addressed and a new master produced and checked before the content can be passed. 

Final Thoughts

In this article we’ve touched on a few of the key points which, if not considered from the outset and throughout the post production process, can potentially cause huge issues. While some members of a post production team may be more creatively inclined than technical, there’s absolutely a need to have people involved who understand the in-depth technicalities which are an unavoidable part of the process. If you’re working on your own then it’s down to you.

Fortunately, we have a fantastic community of people who read the Production Expert blog and collectively we have the knowledge to share with one another. On this, please share your thoughts in the comments about what you feel are the most important considerations for audio post.