Production method for simulcast in 22.2 multichannel sound broadcasting

The 8K with 22.2 multichannel (22.2 ch) sound broadcasting is planned to be launched since December 2018 in Japan. NHK is going to simulcast 2-channel stereo and 5.1 surround together with the 22.2 ch sound for backward compatibility with existing home reproduction equipment, e.g., AV receiver and soundbar. However, individual production for each audio format is impractical because it needs many engineers and a lot of production equipment compared with a production in single format. Hence, an efficient production method for simulcast which does not demand additional production resources is required. The first proposal is a tone compensation for downmixing from the 22.2 ch sound to the other audio formats. The energy spectrum of the downmixed signal is compensated to harmonize with that of the 22.2 ch sound. The second proposal is a loudness chase to have the loudness level of the downmixed signal follow that of the 22.2 ch sound. The loudness level of the downmixed signal usually differs from that of the 22.2 ch sound, so that the loudness chase successively adjusts the loudness level without unnatural level change and matches them by the end of the program.