In our work on sound systems, we are researching a 22.2 multichannel sound (22.2 ch sound) system for 8K SHV and next-generation audio services and working on their domestic and international standardization.

■Adaptive downmixer

  We are studying adaptive downmix technologies for 22.2 ch sound to produce efficiently and simultaneously high-quality stereo and 5.1 surround. In FY 2018, we developed an adaptive downmixer capable of real-time processing by combining coherence control⁽¹⁾ to compensate the tone deterioration due to downmixing and loudness chasing⁽²⁾ to compensate the integrated loudness levels of downmixed signals.

■Reproduction of 22.2 ch sound at home

  We are researching technologies for the easy reproduction of 22.2 ch sound at home. We continued with our study on binaural reproduction⁽³⁾ using line array loudspeakers. In FY 2018, we developed an algorithm for separately controlling each channel and a design method for a reproduction controller optimized for it. We also implemented the design method into our signal processing device. The device was developed in cooperation with Sharp Corporation.

■Next-generation audio services

  We are studying next-generation audio services for advanced terrestrial TV broadcasting. In FY 2018, we added a function to synchronize an audio definition model (S-ADM: Serial-Audio Definition Model, ITU-R BS.2125-0) with audio signals and output them to an MPEG-H 3D Audio⁽⁵⁾ encoder using a digital audio interface. The ADM is audio-related metadata that describes the configuration of sound materials and the location information during playback in program audio. We also developed a real-time audio encoder/decoder using MPEG-H 3D Audio⁽⁶⁾. This led to the successful development of metadata control, object control and rendering functions using S-ADM.
  This research was conducted in cooperation with the Fraunhofer Institute for Integrated Circuits, Germany.

■Acoustic devices

  We have been researching a shotgun microphone, which has sharper directivity than a conventional one. Aiming for better performance in a low frequency band and an environment with diffusive noise, in FY 2018, we developed a microphone that can record target sounds more clearly by using sub-arrays set in the microphone and signal processing in combination⁽⁷⁾.
  We also developed an 8 ch switching amplifier for thin loudspeakers using a piezoelectric bendable electro-acoustic transducer with the goal of realizing a practical 22.2 ch sound loudspeaker for home use (Figure 2-11). This research was conducted in cooperation with Fujifilm Corporation.

■Standardization

  We are engaged in domestic and international standardization activities to promote 22.2 ch sound systems and realize next-generation audio services.
  At ITU-R, we produced a New Recommendation on S-ADM, ITU-R BS.2125. We also added required bit rates for MPEG-4 AAC, which is used for transmitting 22.2 ch sound materials, to the Recommendations on audio coding schemes, ITU-R BS.1548-6, BS.1196-7 and BT.1872-2, on the basis of our evaluation results⁽⁸⁾. We produced new Reports ITU-R BS.2419-0, which describes room response adjustment for 3D sound systems including 22.2 ch sound, and ITU-R BS.2434-0, which describes the standards and examples for loudness levels used in the internet delivery of broadcast programs. We also prepared a Preliminary Draft New Recommendation on the subjective evaluation method of 22.2 ch sound systems with 8K video.
  At the Society of Motion Picture and Television Engineers (SMPTE), we updated a preliminary draft of ST2116, a standard for S-ADM transmission using an existing digital audio interface.
  At the European Broadcasting Union (EBU), we contributed to the development of Tech 3388, a Recommendation on a dedicated renderer for the ADM used for object-based audio and also participated in the preparation of Report TR043 by conducting subjective evaluations on the performance of multiple renderers including our proposed method. We also produced Tech 3392, a Recommendation on an audio definition model (ADM) profile for program production.
  At ARIB, we compiled 22.2 ch sound production guidelines into Technical Report TR-B44. We also prepared a Preliminary Draft Standard for an IP-based production interface based on SMPTE ST2110.
  At the Japan Electronics and Information Technology Association (JEITA) and the International Electrotechnical Commission (IEC), we continued with our works to revise a standard for the general channel assignment for multichannel sound systems (IEC 62574) to add channel labels for various systems including 22.2 ch sound system. Additionally, we produced a standard for transmitting 22.2 ch sound signal stream encoded by MPEG-4 AAC (IEC 61937-11). We also helped the Consumer Technology Association (CTA) revise a standard for transmitting 22.2 ch sound signal stream encoded by MPEG-4 AAC using HDMI (CTA-861.5). At the Audio Engineering Society (AES), we contributed to the standardization of technical guidelines which prescribe that each country's broadcasting rules (i.e., -24LKFS for Japan) should be followed in principle for the target loudness of over-the-top broadcast programs.

 

[References]
(1)	T. Sugimoto and T. Komori: "Tone compensation method for downmixing of 22.2 ch sound," ITE Winter Annual Convention 2017, 12C-5 (2017) (in Japanese)
(2)	T. Sugimoto and T. Komori: "Loudness chaser for 22.2 multichannel sound broadcasting," 2018 Autumn Meeting ASJ, 2-1-14 (2018) (in Japanese)
(3)	K. Matsui, A. Ito, S. Mori, M. Inoue and A. Adachi, "A method to relief the binaural reproduction controller applying output tracking control," Journal of Acoustical Society of Japan, vol.73, no.5, 2017, p.281-290 (2017)(in Japanese)
(4)	A. Ito, K. Matsui, K. Ono, H. Hattori, T. Suenaga, K. Iwauchi, and S. Adachi: "Design and implementation of binaural reproduction controller applying output tracking control," Audio Engineering Society Convention paper 10121 (2018)
(5)	ISO/IEC 23008-3:2015/AMD3:2017 (2017)
(6)	T. Sugimoto, S. Aoki, T. Hasegawa, and T. Komori: "Real time audio encoding/decoding system based on MPEG-H 3D Audio," 2018 Autumn Meeting ASJ, 2-1-13 (2018) (in Japanese)
(7)	Y. Sasaki and K. Ono: "Shotgun microphone with high directivity by extra-long acoustic tube and digital noise reduction," Audio Engineering Society Convention paper 10097 (2018)
(8)	S. Kitajima, T. Sugimoto, S. Oode, T. Komori and J. Urano: "Required Bit Rate of MPEG-4 AAC for 22.2 Multichannel Sound Contribution and Distribution," Audio Engineering Society Convention paper 10078 (2018)