The BBC National(ch 12 B) multiplex has adopted a new configuration where the secondary services from Radio 4 & Radio 5, the BBC Guide and Radio 5 itself sharing 88 kbps of capacity. The main channels have fixed bit rates and the BBC has said that the installation of new encoding equipment has allowed them to reduce the bit rate on Radio 3 to 160 kbps in stereo. The stations in joint stereo at 128 kbps are Radio 1, Radio 2, Radio 4, Radio 1X and Radio 6. The mono stations are BBC 7 (80 kbps) and BBCWS and Asian Network at 64 kbps.

The table may seem a little complex but will become cleared through an example. Normally just four services are broadcast - Radio 5, Radio 5X, Radio 4 and the BBC Guide. If Radio 5X carries live programming then the extra capacity is taken from the BBC Guide. If either of the Radio 4 opt-outs are on the air then provided Radio 5X is not carrying a live commentary it is shut off and the remaining capacity is taken from the BBC Guide. In this configuration Radio 5 gets a temporary boost to 80 kbps. If both Radio 4 and Radio 5 are carrying secondary services then Radio 4 has to drop back to mono at 80 kbps to ‘fund’ its secondary service.

A recent check has shown that the BBC may have abandoned this matrix and gone back to the previous approach of stealing bits from BBC Radio 3 and the data services.