As the ball was hit to the fence for four, Jim Maxwell was just describing the bowler’s run-up on the ABC Grandstand digital radio channel. Steve Ahern went to the cricket and discovered digital ‘latency’ first hand as he listened to his digital radio. He asks, will we ever get real time live broadcasts on digital radio?
Anyone with even a little technical knowledge knows that digital radio has always had a ‘latency’ (delay) effect, because any signal that has to go through a series of computer encoding processes is going to take some time to get to the listeners. It happens on the internet and it happens on digital radio. It is not a new problem, it’s not a problem at all for music stations, and it is really no surprise. But when you are at a sporting event, watching and listening simultaneously, then the phenomenon is quite surreal.
As I sat in the Members Stand at the SCG pondering this phenomenon, I started thinking about whether the problem could ever be solved. Afterall, Voice Over Internet Protocal (VoIP) technology has made real time phone calls via the internet a possibility, and there is similar encoding technology used there, so why could it not be possible in the future to improve the encoding process to the point where there is almost no latency?
There are three elements to consider in the path from the studio to transmitter for digital radio: the linking from the studio itself, the encoding process at the multiplex, and the decoding process in the receiver. At each of these points delay is introduced. If you can shave even a little time off at each point you can reduce the broadcast delay considerably.
Any station that is broadcasting any live sport should be working hard to minimise delay at all of the points in the transmission chain, and, in my opinion, the Australian radio industry as a whole, should be leading the world in trying to make the system as good as it can be. We have become a world leader in digital radio with our pioneering thinking on the medium so far, this problem should be next on the list to solve.
As I consulted some experts, I found a few optimists who thought that one day a solution might be possible, but there are a lot of others who think it will be very difficult, if not impossible.
CRA’s Joan Warner, one of the people who has played a huge part in bringing digital radio to Australia, lists the individual elements of how the latency happens like this:
Audio encoding delay – 0.3 seconds. (this is the delay for the encoder to turn audio into DAB+ audio)
Service Multiplexer Buffering delay – 0.4 seconds
Service Multiplexer error protection delay – 0.2 seconds
Ensemble Multiplexer Buffering delay – 0.8 seconds
Ensemble Multiplexer error protection delay – 0.8 seconds
Transmission interleaving delay – 0.768 seconds
This means that DAB+ digital radio should come out of your speakers of your radio just a little over three seconds after leaving the studio. But some commercial broadcasters currently have their audio buffering delays set higher than this, to improve performance and robustness of the signal. However this then introduces greater delays.
Warner says minimising latency is particularly important for stations such as 5AA in Adelaide and Skysports in Sydney. “They have a latency of about 3 to 4 seconds so people can watch a football game or race with the radio commentary as close to time as it is possible to get.”
Stations with prerecorded programming and talk stations, which already run in delay for legal and profanity reasons, have less concern about the length of the delay than do stations which predominantly broadcast live.
To explore the topic more, I got a discussion going between some of this country’s top radio engineers. Here is what they thought.
Broadcast Australia’s Peter Kepreotes is an optimist. He says “theoretically the problem can be fixed by having no audio compression… but this means a lot more mux capacity needs to be allocated.”
Kepreotes suggestions of how to one day solve the problem are:
1. System latency: ultimately what matters is to minimise the overall system delay in getting the signal to air, so we need to look at minimising delay from all the elements of the production chain including contribution links, studio equipment, encoders. Etc.
2. Live Events: perhaps for major live events, broadcasters could consider running less compression, trade off higher audio quality for reduced latency but need to use more mux capacity. Broadcasters could liken it to say a HD TV signal, the better the quality the more mux capacity allocated to a service. In other words an ‘HD’ DAB+ Radio service would have less compression thus lower latency but allocate higher data capacity.
Poul Kirk a digital sceptic from way back, believes it “is an unfortunate and inescapable fact that Digitizing Audio takes a small amount of time. Decoding of the Digitized Audio also takes a small amount of time. In addition to this, the Digitized Audio must be transported to the Transmitting System.”
For a simple DAB+ transmitting system, explains Kirk, the digitised audio from the studio is fed through an audio processor, a digital Studio to Transmitter Link or data path, into the Multiplex Assembler, then from this into the transmitter. It is then transmitted, received and decoded in the DAB+ receiver.
He also makes the point that for sports broadcasts, you may have one additional digital program data path, and two satellite paths, (eg Melbourne Cricket Ground to Sydney Master Control and return from Sydney MCR to Melbourne MCR and Tx). “Total propagation delay from microphone to receiver for this could be as much as 6 Seconds making the commentary sound silly in relation to action on the sports ground,” according to Kirk. He suggests low powered Fm transmitters at the sporting venue for local spectators to listen in real time.
Former Austereo technical head Des DeCean who is now a consultant and currently Chair of the digital radio taskforce, says the commercial radio sector has already “spent considerable time reviewing ways of reducing latency.” Initially it was around 5 – 6 seconds, but it is now down to around 4 seconds.
DeCean says this was a particular concern for Racing Radio’s Max Carter and that Australia is already quite well ahead in reducing latency thanks to the importance placed on the issue by people like Carter.
DeCean says a reasonable amount of latency results from the desire for good error correction, making sure the signal is good quality for listeners. It appears to become a balance between signal robustness and being close to real time.
CRA’s Richard Morris is currently writing a paper on this subject, according to DeCean. “In that he attributes about 3.7 seconds delay to various error correcting, buffering and interleaving aspects of the transmission system, and just 0.3 seconds to the DAB+ audio encoder.”
DeCean says he is “not optimistic that the delay can be reduced without major changes to the architecture of the DAB+ system. Not that this is out of the realms of possibility, but it would render all current receivers obsolete, therefore making change somewhat difficult to introduce.”
Getting back to the cricket… I spoke to a senior engineer at the ABC about Jim Maxwell’s delayed descriptions. He did not wish to be named, but he told me delay has got much better since digital radio was first introduced, when it could have been as much as 15 seconds under some conditions.
He told me that ABC Radio has reduced the amount of delay resulting from links to the venues and satellite hops quite a lot, but that more could be done on this issue to ensure minimal delay from internal processes.
But as for the digital radio latency, he is not hopeful. “I don’t see that we will ever be able to eliminate it completely.” He also made the point that different digital radio receivers have varying decoding times, generally the more expensive ones are quicker while the cheaper ones are slower.
Despite all this, I am an optimist. One day I believe I will be able to sit in the stands, watch the game and listen to it on my digital radio in real time.
Sometimes all it takes is for someone to articulate a problem and set a goal, then hand it over to brilliant engineers who will take up the challenge and figure out how to fix it. There are plenty of those in Australia. Over to you guys!
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