Immersive Audio with TouchMonitor

September 9, 2019 by Mike Kahsnitz

Mike Kahsnitz Senior Director of Product Management, RTW

September 9, 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.

TruePeak Levels

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.

PPM with TruePeak Warnings

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.

PPM-Style Loudness

Channel Distribution

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.

The PPM is also well suited for detecting mismatches in the channel layout, e. g., if someone has confused L-R-C-LFE-Ls-Rs with L-C-R-Ls-Rs-LFE.

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.

The Immersive Sound Analyzer

Stereo Image

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.

Das PPM ist auch gut daf r geeignet, Fehlanpassungen des Kanal-Layouts aufzudecken, z. B. wenn jemand L-R-C-LFE-Ls-Rs mit L-C-R-Ls-Rs-LFE verwechselt hat.

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.

The Audio Vectorscope

Phase Relations Between Channels

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.

Loudness across the 5.1 main and the 4.0 upper bed.

Designing the Immersive Display

Now lets 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, Ill create one stereo audio group and add PPM, Loudness and Vectorscope, and Ill 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

LINK:	https://www.rtw.com/blog/welcome-to-our-blog-1/immersive-audio-with-to...
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