London, UK (July 15, 2005)–On July 2, the Live 8 series of concerts held in London, Philadelphia, Paris, Berlin and Rome were broadcast to a worldwide audience of millions. In the UK, Capital Radio took responsibility for the distribution of the worldwide and London Hyde Park feeds to the majority of commercial radio groups, such as Chrysalis, Emap radio and GCap Media, using the APT WorldNet Oslo codec.
Supplied by Mark Thom of Broadcom Ltd, APT’s UK Distributor, and installed by BT, the WorldNet Oslo delivered seven stereo feeds from the BT Tower to Capital Radio’s facility in Leicester Square, about two miles away. There were three main parameters the WorldNet Oslo was required to fulfill: Seven stereo feeds had to be sent over one E1 circuit, the audio quality had to be similar or exceed the existing J.41 solution and the coding delay between the two facilities needed to be less than 5 milliseconds.
Mark Woodhouse, the chief engineer with Capital Radio, compared the WorldNet Oslo to the existing E1 link, which utilizes BT Musicline 2000 codecs (branded RE/Barco), which support only five 15kHz channels, normally configured as two stereo and one mono. “Regarding the audio quality, it is probably worth pointing out that the J.41 data reduction scheme used in the Musicline 2000 is a companding technique, which takes a 14-bit word and reduces it to 11 bits. As such, the dynamic range of J.41 limited to 84dB. Using +18dBu as headroom, this ensures the ground floor level is around -66dBu, however Enhanced apt-X using 16 bit has a dynamic range of 96dB and can drop the ground floor level by an extra 12dB to – 78dBu. The acoustics, linearity and the spectral imaging of the WorldNet Oslo was of exceptional quality.”
Happily, the WorldNet Oslo more than matched the J.41 setup to provide an end-to-end processing time of around 4.5 milliseconds.