22.2 Multichannel Audio Coding and Dialog Channel Control Function

NHK’s 8K Super Hi-Vision (8K) broadcasting system has 22.2 multichannel (22.2 ch) sound as its sound system. 22.2 ch sound uses 24 channels that produce highly immersive surround sound giving listeners the feeling as if they were actually at the site. (Figure 1)

8K Super Hi-Vision’s audio coding scheme for transmitting 22.2 ch sound is MPEG-4 AAC^*1. MPEG-4 AAC is capable of compressing the 25-Mbps LPCM (linear pulse code modulation) signal of 22.2 ch sound down to approximately 1/20th of its original rate, or 1.4 Mbps.

With the aim of improving the functionality of 22.2 ch sound as a broadcasting service, a domestic standard has been established for its control functions, including the dialog (speech) enhancement for the program narrative and speech at a receiver, and a dialog replacement function. In a dialog-channel-control-capable program (Figure 2), a viewer can freely adjust the volume balance between the channels for the dialog and those for background sound to their personal preferences and individual listening environments. The dialog replacement feature has further application potential in multilingual broadcasting and commentary broadcasts and may lead to a new broadcasting service that meets the individual needs of our listeners.

STRL constructed an 8K coding system equipped with these functions and conducted a transmission experiment via a broadcast satellite at the STRL Open House in 2015. The experiment verified the high quality transmission capability of 22.2 ch sound, as well as the effectiveness of the dialog channel control function. We will continue with the development of program production systems with the dialog channel control function capability.