Bringing IP audio home

40AoIP is a great commercial audio trend, but it’s not yet appropriate for the residential market. Anthony Grimani explains.

The pro and commercial audio industries are rife with initiatives and standards for Audio over IP (AoIP). These present a way to forego the multitude of analogue connections otherwise required for a switching matrix and to keep everything safely in the digital domain. And they offer huge advantages of simplicity, flexibility and reduced installation times.

All the audio sources and destinations are connected through networking switches and the matrixing decisions and setups are handled through PC applications. It’s like utopia for integrators that want to offer high-value propositions to their clients. Should this not also be used in the high-end residential world?

Unfortunately, the market is fragmented by several incompatible and competing schemes. You have to be careful to select the right products from the various manufacturers so that the signals all function properly. Options include Dante, RAVENNA, AVB, Cobranet and Q-LAN, among others. A recent initiative in everybody’s mindshare, called AES67, is an interoperability standard for AoIP. It is promoted through the Media Networking Alliance (MNA).

If it really works as claimed, this unifying technology will allow more brand and product selection flexibility – in an effort to reduce wiring complexity and improve interoperability.

Note that MNA companies are all in the pro and commercial audio industries; no one seems to have looked at the needs of the residential integration industry.

I went around the recent ISE show in Amsterdam asking some pretty basic questions and got mostly blank stares. “Never mind,” I said, “I’ll just go to the ‘Coffee Shops’ instead and ruminate on the items we would need to make AoIP successful for home cinema and whole house AV applications.”

After some cogitation, I determined that the main issues we need to worry about are synchronisation, latency and controllability.

Issue 1: Synchronisation.

For surround systems from 7.1 channel to Dolby Atmos 9.4.4 to sound exactly right, the speaker signals need to reach the listeners’ ears within 0.1ms of each other. I know that’s an extremely tiny window, but I suggest you listen to the effects of slowly incrementing the delay of the centre channel in 0.1ms steps while listening to a test signal with centre and left reference pulsed noise.

You will hear the image shift from the centre of the sound stage to the left, with really only a few steps where the image is convincingly where it should be – at the mid-point between the left and centre speaker.

The same goes for a test of left and side left. You can get such a test disc, called the 5.1 Audio Toolkit, through Wavetrain. Just follow the menu instructions to get to Title 1, Chapters 20 through 24. The problem is that, when I asked the various proponents of AoIP how accurate the sync would be, they all seemed to think it didn’t matter – or that it would be within a few milliseconds.

It may not matter when you are distributing public address announcements around an airport or conference centre, but it sure matters a lot in a home cinema! I also think that in whole house audio, the sync needs to be better than 0.1ms if you don’t want to hear annoying comb filter interference as you walk around the residence.

Issue 2: Latency.

The picture-to-sound synchronisation for a good quality home cinema should be better than 15ms. That is about half a frame of regular film rate. Longer errors than that cause the dialog to feel soft, footsteps to be ethereal and the whole dynamic falls apart. While multi-zone sync can be kept within a few milliseconds, according to the various AoIP proponents, they often trade that against overall latency.

Once again, that’s not a problem in commercial environments, but excess latency is just not acceptable for sound that has to match picture content. I would also argue that, for a band to perform well on stage, the latency from the sound reinforcement should be kept low, too!

Issue 3: Control.

Yes, it’s all about control and I didn’t get any straight answers about how prepared the various switchers, processors, amplifiers, etc., were to receive commands from control systems made by the usual suspects in our industry. I was generally pointed to configuration applications running on computers as the solution to it all; this is not OK if you want to simply hand a touch screen or a handheld remote stick to one of your techno-averse clients…

So maybe the people I was talking to during the world’s largest AV integration show were not the right ones, or maybe these AES67-touting folks aren’t at all aware or interested in our market potential. That’s all too bad. When I look at the back of a rack of gear set up in the AES67 way, I get jealous. It’s clean, simple and pretty bullet-proof. Just a bunch of Cat 5 or Cat 6 cables dressed neatly over to a set of routers or switches and voila; all done for the day! Time to go out and get some drinks to celebrate another fine day in AV heaven.

On the flip side, I see you guys inhaling more solder smoke, burning your fingers with the overheated insulators and desperately trying to see which XLR pin is labelled ‘2’ in the semi-darkness of the bowels of a rack – unable to focus on the tiny numbers because your reading glasses are lost somewhere in the car…

There may be some new future work that would resolve our conundrums. The AVB/TSN (Time Sensitive Networks) initiative, along with some professional Video over IP initiatives and standards, may be our ticket to simpler interconnections and more robust operation. May I suggest that you ask a lot of questions to your suppliers and stay closely tuned to the news from the AES67 group? Maybe someday, you too will get away from the job site early, share a few beers with good friends and loose less of your precious margins to complex and troublesome analogue patching and routing. Oh and remember, I have a degree in Electrical Engineering with a specialty in analogue systems and RF modulation schemes. I know how much of a pain all this is!

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Reference: Connected Home

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