Immersive Audio, TouchMonitor, Broadcast

Immersive Audio With TouchMonitor

In my previous blog, I talked about the audio channel layout that will be used at the Olympics in 2020. In this article, I'll dig further into how TouchMonitor can be set up to monitor immersive audio at typical sports events.

Mike KahsnitzSeptember 09, 2019

What needs to be monitored?

With its simple and flexible user interface and the capability to monitor up to 32 audio channels simultaneously, the TouchMonitor very much fits the needs for monitoring immersive audio streams, whether used by engineers in production or used at any point in the transmission chain.

And with the new Immersive Sound Analyzer the TouchMonitor tool box has just been expanded to cover demanding immersive applications.

First, let us take a closer look at what it makes sense to monitor if you work with a typical immersive audio stream in broadcast.

I will design a 16-channel screen layout according to 5.1.4, one stereo pair and 4 objects, but it can of course also be done with two stereo pairs and two objects, or even with 7.1.4 based audio layouts.

The screen layout is made with Dolby® Atmos™ in mind, and requires optional software licenses such as our new software license "SW20015 ISA - Immersive Sound Analyzer".

Below you see an overview of the 16 audio channels, the layout and what I recommend to be monitored.

True-peak Levels

PPM with True-peak Warnings

In most production scenarios, engineers need to keep an eye on the PPM level per channel, including true-peak warnings.

Naturally, it is important to monitor if there is in fact a signal present on the channel, but also, and this is equally important, to monitor whether audio overloads occur.

The PPM is also ideal at revealing channel layout mismatches, for instance if someone confused L-R-C-LFE-Ls-Rs with L-C-R-Ls-Rs-LFE.

As we know, audio true-peak overloads can create a large number of problems downstream, so it is important to keep an eye on this aspect constantly. The white line on top of each bar is a TPmax marker that makes it easy to identify TP overloads on specific channels.

Worldwide regulations (EBU R128, CALM Act and more) require broadcasters to guarantee true-peak levels within specific limits for each audio channel. The PPM meter in TouchMonitor fully complies with all international standards.

Loudness

PPM-Style Loudness

All audio groups should be monitored with regards to various loudness measures.

We recommend that the main- and upper beds as well as the additional stereo channels plus the objects are all monitored on momentary and short-term loudness as those measures give you a clear picture on the perceived levels of each group.

With TouchMonitor, there are a number of ways to display momentary and short-term loudness, including a PPM-style meter as the one you see on the right.

Channel Distribution

The Immersive Sound Analyzer

You would also need to keep an eye on the distribution between the audio channels in both the 5.1 layer and the 4.0 layer.

By using the Immersive Sound Analyzer, you can make sure to spot if your audio material is not balanced correctly, and you can keep an eye on the subjectively perceived acoustic focal point.

Also, the Immersive Sound Analyzer will indicate phase problems and show you the stereo width between each of the speakers within their bed.

To learn more about the Immersive Sound Analyzer, you might want to read this blog post.

Stereo Image

The Vectorscope

Beside PPM/True-peak and loudness, the channels outside the 5.1.4 main and upper bed should be monitored with regards to image and phase problems.

It naturally depends on the content, but it would be natural to choose the Vectorscope for this purpose.

Most importantly for this setup, the Vectorscope shows the stereo image. Beside that, it reveals phase problems as well as stereo balance problems.

To learn more about the Vectorscope, you might want to read this blog post.

Loudness of the 5.1.4 Program

Loudness across the 5.1 main and the 4.0 upper bed.

It is key to be watching the overall loudness numbers for the 5.1.4 main and upper beds combined.

The Immersive Sound Analyzer for TM7 and TM9 lets you do just that: measure loudness across audio groups.

 

Designing the Immersive Display

Now let's dig into designing the actual immersive TouchMonitor screen layout.

TouchMonitor is highly flexible with regards to designing the screen layout, so you can naturally design your own, but this is my take on a highly functional screen layout suited for immersive audio.

Before designing the actual display you need to make sure that you have created the necessary audio groups and set them up correctly.

1. Create a 5.1 audio group for the main bed, and setup the input routing. Add PPM and Loudness to the audio group.

2. Create a 4.0 audio group for the upper bed, and setup the input routing. Add PPM and Loudness to the audio group.

3. Create audio groups for each of your objects. In this case, I'll create one stereo audio group and add PPM, Loudness and Vectorscope, and I'll create 4 mono audio groups, and add PPM and Loudness.

4. Create the Immersive group. In this group you add at least the 5.1 main bed and the 4.0 top bed as immersive content. Select the desired loudness standard. The Immersive group will overwrite any settings in the audio groups for the two beds to guarantee correct operation. Also the weighting factors will be set.

As a power user you know that there is a difference between a 4-0 group in a main bed and a 4-0 group in a top bed when it comes to the gain of the rear speakers.

The Immersive group will also automatically start instruments like the Surround Sound Analyzer or the loudness in the audio groups for the beds as it requires to get data from there.

If you check the settings of the two bed audio groups, you will find that some settings are now greyed out and locked.

Now it is time to go to the screen-layout editor to set up the screen.

TouchMonitor Screen-layout Editor

5.1.4 Main and Upper Beds

The 5.1 main bed section is designed to show true-peak PPM, M, S and I Loudness and similarly, the 4.0 upper bed section shows true-peak PPM, M, S and I loudness.

The Immersive Sound Analyzer shows the surround images for both the main and upper bed in one easy to read window.

On top of this, I have added a section that shows the M, S and I Loudness as well as LRA for the main and upper beds combined.

5.1 Main Bed and 4.0 Upper Bed Sections with the Immersive Sound Analyzer

Stereo Pair

I have designed the stereo section to show true-peak PPM as well as momentary, short-term and integrated loudness as graphical bars.

Further, I would recommend using the Vectorscope to let you keep an eye on the stereo image as well as the phase.

Stereo section

The four objects

Each of the 4 objects should be monitored with regards to true-peak PPM.

Like the stereo pair, I have set up only a momentary loudness graphical bar, and I have added momentary and short-term loudness as numerical values.

Not knowing what the final mix at the end users place will be, for most productions you would want to ensure consistency between the objects to avoid loudness jumps and other artefacts, so the loudness measures are key on this setup.

As you see, I have marked each of the audio groups containing the objects with different colors for a better overview.

Section with 4 Objects

Adding a Set of Convenient Buttons

As a last thing I will add a set of buttons.

START, STOP and RESET are always convenient to have at hand for starting and stopping measurements and to reset loudness calculations.

The buttons shown are part of the Global Keyboard and linked through all audio groups to synchronize start/stop of the integrated measurement as well as to reset all measurement stored in memory: TPmax, Mmax and TP-hold per channel.

The final screen layout

Here you see the final screen layout displaying the entire immersive audio stream, combining all of the above.

Useful for immersive live broadcast production, as well as monitoring the broadcast transmission path.

 

The Screenlayout Tailored for Immersive Audio

Alternative: Individual Analysis of Each Bed

As an alternative, you can use the Surround Sound Analyzer to measure each of the of the audio beds individually.

This leaves less space for other measures such as overall loudness, but might make more sense if you need to monitor phase correlation between each speaker in each bed simultaneously.

Immersive Audio Screenlayout with two Surround Sound Analyzers

 

   


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Practical Use

This screen layout can be used in a various immersive audio scenarios, and it was designed with consultancy from major international sports production companies.

  • Immersive audio transmission
  • Compatible with Dolby Atmos or MPEG-H
  • Live Broadcast Production of sports events and more
  • Monitoring the transmission path
  • Keep an eye on the stereo- and surround-image and focal point of the main beds
  • Check phase relations on all relevant layers
  • Make sure to avoid true-peak overloads, creating problems downstream
  • Surveil important loudness measures to comply with standards and make sure to loudness align objects

What do you need?

A TouchMonitor TM7 or TM9 can handle 16 channels of audio via AES3 and 3G SDI. In combination, the interfaces can handle even more channels, up to 32. The TouchMonitor versions with AoIP connections can handle up to 32 channels, more than sufficient for metering and analyzing immersive audio in broadcast.

Because of the many details on the screen, we recommend the TM9 with the larger 9" display, but you can also use the TM7.

TouchMonitor is structured in so-called audio groups. Each audio group consists of up to 8 audio channels, and you can create up to 8 audio groups, which is plenty to support broadcast immersive audio.

On the software side, you would need the following software licenses for an optimal immersive setup: