DAB+ & DMB being trialed in France

Despite it being expected that France would only use the DMB system for digital radio, and Ofcom criticised the French regulator's decision to do so, both DMB and DAB+ are being trialed in France after all.

A pdf for the Towercast DMB trial multiplex in Paris also provides a breakdown of how the bit rate for each channel is allocated between audio, video and total including overhead, and when you compare these figures with DAB+ you see what a terrible decision it is to use DMB. A pdf of the DAB+ trial details in English is also available.

The following table compares the bit rate level that's available for audio on DMB and DAB+ when the amount of multiplex capacity is the same. The table uses actual figures from the Towercast DMB trial and copies figures from the DAB+ specification (Annex E on page 24, 24 kHz column in table) for the stations that are using 2 kbps for video on the Towercast DMB trial.

Basically, what you have on DMB is that in order to allow a 2 kbps video stream, which will consist of a still image being changed occasionally (2 kbps is nowhere near a high enough bit rate for proper video), about 19 kbps of capacity is wasted on overhead. With DAB+, this 19 kbps can be used to improve the audio quality -- e.g. using 80 kbps instead of about 60 kbps for the AAC+ audio. And for stations using low bit rate levels of around 60 - 80 kbps, a difference of 19 kbps would make a huge difference to the audio quality. Therefore, the use of DMB will without question lead to the audio quality being worse than if DAB+ had been adopted.