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Freeview HD sound problem: solution found

The BBC says it's found a solution to the sound problem that has been affecting some Freeview HD users during the past six weeks.

In March, a516digital and other websites started to receive queries about sound dropouts on certain Freeview HD channels. Soon it became clear that devices from Samsung and Toshiba were prone to this problem, which affected BBC One HD, BBC Two HD, ITV/STV/UTV HD, Channel 4 HD and CBBC HD - channels carried on Freeview using BBC capacity.

Following a lengthy investigation and appeals from the public for assistance in identifying all the devices that were experiencing the problem, the BBC now says it's in a position to make some changes it says will help the affected televisions.

According to a statement issued by the BBC, the changes will be rolled out on a region-by-region basis, starting in Scotland, Wales, Northern Ireland and London.

The BBC said:
"Rolling out regionally will enable us to monitor the impact, just in case we need to reverse the changes, if unexpected problems occur. Assuming it works successfully, we will roll out to the rest of the country in the next couple of weeks"

For the first time, the BBC has revealed what caused the problem: perceptual noise substitution or PNS, which under certain circumstances was being used by their encoders. Explaining the technical side, the BBC said:
"PNS is part of the MPEG4 AAC specification which the UK D-Book* references.  Our encoders have always been capable of using PNS but a recent update meant that PNS could be selected by the audio encoder at the audio bit rates used on Freeview. "

Manufacturers, meanwhile, are planning their own software updates to provide a long-term solution to the problem, although the BBC believes these updates may still be a few weeks away.

UPDATE 19/05/2016: The regional rollout has now completed.

* The "D-Book" is a publication for broadcasters and manufacturers, created by the DTG, that specifies various standards that devices need to meet in order to be fully compatible with Freeview or Freeview HD.