Broadcast Audio System Design: Part 1 – Overview

We begin our series on things to consider when designing broadcast audio systems with the pivotal role audio plays in production and the key challenges audio presents.


Other articles in this series:


When it comes to broadcast networks, the consensus is that audio is the most difficult thing to get right. It seems unfair, no?

Surely video, with all its visual wizardry is more complex? Or lighting rigs, with their hundreds of lights to add drama or clarity to a production, is more complicated to set up and manage?

In terms of infrastructure, video and lighting are standalone. Neither acts as a central axis to the wider production or has to interact with as many parts of the production process as audio.

Audio networks represent the central nervous system of television. It’s not just about how things sound; while the audio control room is ultimately responsible for mixing incoming feeds for transmission, it also coordinates instructions to everyone on set; it ensures that remote feeds are live; it tells people when to be quiet and when to speak, and to be gracious while doing so.

An audio network must be flexible enough to ensure that the right people hear only what they need to hear to do their jobs effectively.

And as distributed production and remote production methods become more commonplace, and IP technology is introduced across all broadcast disciplines, those challenges become more nuanced.

In short, without a robust and reliable audio network, a TV production studio is just a collection of people wandering around and silently mouthing at each other. The audio network is the glue which holds everything together.

What’s In An ACR, And Why: Mixer And Comms

At the heart of the Audio Control Room is the mixing console.

The mixing console has always been at the centre, although with shifts to distributed working this traditional model is changing. The console manages every audio input and every audio output, and feeds into other equipment such as comms systems.

Theoretically, any audio console can mix broadcast audio, but there are features on broadcast consoles which you won’t find anywhere else.

For example, broadcast consoles will often have enormous routers because broadcast productions can have hundreds of people to keep in the loop. With so many voices, nobody wants or needs to hear everything, so thorough and comprehensive planning of all audio connectivity is fundamental. This applies to inputs, outputs and internal mixes.

Planning is everything - who needs to hear what, why, from whom and when?

Camera operators need to hear instructions from the director, location reporters need to hear questions from the studio, runners need to know who they need to be with and where they need to be, studio talent needs to hear what’s coming up next, when they are live to air, when the broadcast cuts to a news item; they need to hear research during interviews, live developments, their co-hosts, location reporters and themselves.

The console feeds into a comms system which adds a layer of talkback to keep everyone in the loop, but each auxiliary mix might be different and they can be complex to set up (which is why a mixing console needs to make good use of memories).

Broadcast consoles make it easy to create mix-minus feeds for interruptible foldback (IFB) to enable simple communication from the Gallery. A mix-minus feed is an efficient way to send a full mix to multiple listeners, minus their own input. A typical broadcast infrastructure needs lots of them.

Monitoring

Monitoring is not just about speakers, although speaker placement and acoustic design is a key aspect to any ACR design – and in rooms where space is limited, like outside broadcast trucks, it’s even more challenging. There may be multiple output formats, from mono to stereo, 5.1 surround and full Immersive mixes, and with the rise of audio personalisation using audio objects, operators have to keep across a lot more than they used to.

Modern distributed workflows add further complications, and monitoring input and output signals in a bedroom or a garage introduces different and unique challenges.

But monitoring is so much more than what something sounds like. At its most basic, audio monitoring is about guaranteeing quality of service as well as adhering to broadcast legislation in any given territory.

Loudness measurement is fundamental – the EBU and the US both have different rulings which broadcasters must adhere to. Monitoring also checks incoming signals are live and that international comms are operational, or that all downmixes are intelligible. It means ensuring that all output formats are metered and monitored, whether they are transmission feeds, international feeds, language objects or multitrack outputs for repurposing or ingest.

Glue

There are a range of specialist products in a studio environment which can monitor and automate much of this, and as technologies develop and consumer expectations change, these products will need to adapt with them.

They are often referred to as “glue” products in that they stick everything together. They can automate processes, enable things to talk to each other, or help a broadcaster adhere to changes in international regulations. They include products like downmixers/upmixers, monitors, external EQ and dynamic processing, metering and distribution amps.

As the broadcast industry embraces IP infrastructures, these products can help bridge the gaps with Gateways and converters to IP codecs like Dante and AES67 to enable hybrid and full IP networks, and as the industry moves to more distributed production to improve flexibility, they can enable remote connectivity of audio as well as video signals.

Where Is The Room?

Post-Covid, location has become much more of a consideration for television production. Remote working and remote production are both established workflows which broadcasters are embracing to reduce costs, increase content production and maintain quality.

From an audio point of view, there are some fundamentals to consider. Everything we’ve covered still applies in a distributed production model, but there is no longer always a central hub.

Plus there are big differences between remote working and remote production. The easiest way to understand it is to ask is where the processor is – and that’s even before we talk about the cloud.

Latency

Let’s look at a single impact of location.

Latency is the time it takes for a signal to journey from the input (a mic) to an output (such as an earpiece). It’s generally accepted that latency of more than 10 milliseconds in an earpiece can become noticeable and can affect performance.

The big problem with audio over distance is that it adds latency.

For a live event which is being mixed on the other side of the world, with local processing at the studio, that distance is doubled. For a presenter who wants to hear themselves in their own ear, the signal has to travel the distance to the control room and back again. Traditional outside broadcast setups don’t have this issue as processing is done at the same location, so there is no latency caused by distance.

Flexible access to processing cores can counter this effect – control access from a studio console to a processing core at the talent’s location eliminates the problem. This is remote broadcasting. Remote access to a processing core in a studio or a truck from a remote location, such as someone’s kitchen, is remote working.

Remote working covers control of the processing core from a mixer, or from a cloud-based user interface which talks to the core, wherever it is. This is not to be confused with mixing in the cloud, which refers to the control of audio processing hosted on a server, but remote control of on prem or edge processors.

In all these environments, reliability is still paramount and so connectivity needs careful consideration, whether that is over leased (so-called “dark”) fibre, or using equipment designed to aggregate connectivity paths to work in remote locations.

We Need To Talk About IP

Irrespective of whether it’s a studio, mobile or a remote location, all ACRs need to consider infrastructure. More new builds are designed around flexible IP infrastructures, and common protocols are in place with adherence to SMPTE 2120-30 for audio.

As the acknowledged IP standard for audio, AES67 was rolled into the SMPTE 2110 standard, although 2110-30 adds some more details, such as support for IGMPv3 (which enables multicast streaming). SMPTE 2110-30 also states that devices should support a wider range of Precision Time Protocol (PTP) parameters, and that Real-time Transport Protocol (RTP) streams allow for a media clock offset of zero to allow faster initialisation of streams.

IP opens up a can of digital worms, and synchronizing signals should be at the head of any IP audio network. The main broadcast IP protocols (Dante, Ravenna, AES67 and SMPTE 2110-30) all rely on PTPv2 for synchronization.

When we talk about specialist external products, this is the Grandmaster of them all, in every sense of the word, and every modern Control Room should plan for a PTP Grandmaster to provide sync to the entire infrastructure.

The Console

In the second part of this article we’ll look in some more detail at the equipment which has always been in the centre of it all – the mixing console.

You might also like...

The Basic Principles Of Production Control Room Design

Designing and building a production control room means different things to different people and is often accomplished in a myriad of ways.

Ashley Xu - Crossing The Divide Between Creating For Social Media And Traditional Professional Media

Ashley Xu blew up on social media when she started making ‘thirst traps’ (adverts) in her college dorm. Check them out, you may be surprised by just how good they are. It did not take long for major brands to see…

Audio Post For ‘Billions’ With Eric Hirsch & Gregg Swiatlowski At Goldcrest NY

The multi award winning team at Goldcrest share their creative insight and technique through an exploration of the subtle soundscape for Billions.

Podcast Studio Design: Getting The Room Right

Podcasting is an increasingly popular pastime in the U.S., with an estimated 120 million podcast listeners in 2021. Back in 2006, only 22 percent of the adult population was aware of podcasting. By 2021, this figure had risen to 78 percent. Podcasting is becoming an…

Broadcast Audio Workflow: Part 2 - Entertainment With An Audience

We continue our discussion of broadcast audio workflow with multi-award winner Robert Edwards. We look at the many challenges that come when a live audience is added to the broadcast mix.