In 2006, large-screen flat-panel TVs are likely to attract attention for their audio. Makers are eager to leverage audio quality to distance themselves from the competition.
"More and more music is just full of distortion. We want to eliminate it, and recapture the sound of the original music," said Toshiharu Kuwaoka, senior staff engineer, Engineering Dept, Audio/Video Systems Category of Japan Victor Co Ltd of Japan. More and more engineers in the audio technology field are expressing the same feeling.
Much of the problem stems from the fact that there has been a very rapid jump to the next generation of audio-visual (AV) equipment. Worldwide, televisions are evolving from conventional cathode ray tubes (CRT) to flat-screen models such as liquid crystal display (LCD) panels and plasma display panels (PDP). The thinner TVs have contributed to a sharp drop in audio fidelity, because the thinner cases are unable to provide the depth used by speakers in CRT designs, degrading bass reproduction fidelity.
In audio players, systems supporting digital sound sources are rampant, including hard disk drive (HDD) models and Flash memory designs. During high-efficiency encoding, however, glossy techniques cause information such as certain frequency components to be dropped. In many cases, the amplifier and other output circuitry and components offer only minimal performance.
While TVs and portable music players are immensely popular, neither offers satisfactory audio fidelity, say many technicians in the field.
On the one hand, digital sound sources are steadily trending toward higher audio fidelity, digital broadcasting, next-gen digital videodisc (DVD) and broadband, and significant growth in storage capacity is expected. This is boosting audio signal bandwidth and dynamic range, supporting the shift toward multi-channel (3D sound field) technology. If these high-fidelity sound sources can be used, it is possible to create a highly realistic audio environment, and the sensation of "being there".
The higher fidelity that sound sources can offer, the more consumers will be able to tell the difference. And 2006 is the year that original sound returns.
In 2006, large-screen flat-panel TVs are likely to start attracting attention for their audio. There has been intense competition in improving picture quality in flatscreen TVs over the last few years, and as a result it has become difficult to grade models by the beauty of the displayed imagery. Some appliance manufacturers are beginning to shift their sights to audio, accelerating product development in the field. Audio technologies such as 5.1 channels, for example, which have been pretty much limited to high-priced home theater systems, are beginning to appear in mid-price flatscreen TVs. Manufacturers are eager to leverage audio quality to distance themselves from the competition (Fig 1).
High-End Flatscreen TVsTV manufacturers are pushing audio for three main reasons, the first of which is the continuing increase in TV screen si ze. If the pace keeps up, standard home-use TVs will have to turn into home theater displays and offer much better sound quality. Manufacturers are hurrying to build reputations as firms with outstanding audio, in preparation.
TV picture quality is in the mature stage now, and engineers are finally able to turn their attention to audio, which has been pushed to the sidelines until now. Ka
zuhiko Ikeuchi, staff engineer, PDP Mechanical Design Team, PDP TV Engineering Group, Visual Products and Display Devices Business Group, Panasonic AVC Networks Co of Matsushita Electric Industrial Co, Ltd of Japan summed up just how the TV manufacturers feel: ¡¡øImage quality in flatscreen TVs has been steadily improved, and the graininess is all gone. At the same time, it has increased the gap between audio and video quality. The time has come to pay more attention to sound.¡¡¯
The second reason is that rising unit prices for TVs has made it possible to absorb a bit of the audio cost. "CRT TVs have generally only used cheap speakers that cost ¥100 or ¥200 each, even the relatively expensive 36-inchers. With flatscreen TVs, we can invest a little money to tap the latest technology," explained a source at one major TV manufacturer. As a result, engineers are aggressively loading in the very latest auto tech. As Kiyoshi Masuda, manager, Digital Audio-Visual Backbone LSI Development Dept, Audio-Visual Product Development Center, Audio-Visual Systems Group, Sharp Corp of Japan
pointed out, "The 1-bit amplifier technology used in audio systems has finally been used in TVs, after a two year delay. In the future, new 1-bit amp technology will probably be launched in TV applications."
The third reason is rising cost/performance for audio digital signal processors (DSP). In audio signal processing the processing load is not as high as for video, even with improved fidelity and 3D sound fields. A 50MIPS chip can provide excellent performance in both fidelity and 3D sound fields even in a flatscreen. A source at Analog Devices KK of Japan commented, "Back in 1995, DSPs were said to deliver about 1MIPS of performance per US$. The same dollar can buy 53MIPS today," highlighting how high-end performance can be bought for a minimal investment. From 2006 a number of semiconductor manufacturers will be rolling out DSPs with audio processing capabilities, and mostly aimed at televisions. It will make it a lot easier for the TV manufacturers to power up their TV audio offerings.
Many TV manufacturers are researching how to achieve the 5.1-channel audio effect with only the two (left and right) speakers inside the TV. The goal is to achieve the same sound field provided by using two speakers behind the listener for a total of five channels (three front and two rear), plus a sub-woofer for bass.
There are a number of ways to achieve this, such as a head-related transfer function (HRTF) expressing the transfer characteristics of sound propagation from sound source to listener's eardrum, or techniques to use wall reflection. Researchers hope to significantly improve the sound field, providing the same "live" feel as in movies and concerts.
The digital portable music player, launched into stardom by the iPod from Apple Computer Inc of the
US, has fueled major growth in the number of music users. A large number of engineers in the acoustics field, however, express dissatisfaction with sound quality.
When ripping files from a compact disc (CD) to a personal computer (PC), for example, which requires extracting music data, converting it and saving it to the PC, or when swapping music files via the Internet, high-frequency waveband components are cut (Fig 2, p29). A CD includes frequency components up through 22.05kHz, but an MP3 encoding speed of 128kbps and sampling frequency of 44.1kHz would eliminate almost all frequency components of 16kbps or higher.
While music players were originally designed to play these stripped-down audio files, the situation has changed dramatically of late. Today's models are expected to offer Gbyte-class onboard storage, while an increasing number of music files decrease the coding rate to boost fidelity. As a result, even portable players are beginning to use high fidelity as a sales point. A number of firms are playing with compensating the narrowed bandwidth caused by high-efficiency encoding in an attempt to create a signal closer to the original CD track, and some solutions are already on the market. 
These audio technologies will find application in more than just AV systems, though (Fig 3, p29). If common technologies are utili
zed in a wide range of fields such as games, business and welfare, it could easily lead to whole new product genres, creating new characteristics and new attractions in products.
Games are using HRTF to achieve surround acoustic effects with a limited number of speakers. In the game sector, including mobile phone games, a technology is already on the street to control apparent sound source position (sound image localization technology). NTT DoCoMo Inc of Japan, for example, implemented the technology in its FOMA 901i series of mobile phones released in 2005. The technology was provided by Sonaptic Ltd of the UK and Matsushita Electric Industrial.
NTT DoCoMo has disclosed an application programming interface (API) to enable game developers to utilize sound source localization information in the mobile phone. It is possible to define the distance, azimuth and elevation to the sound source from the user's position. NTT DoCoMo says that it was able to implement sound source localization with only a relatively small amount of data, having a minimal effect on fees.
Professor Yoichi Suzuki of the Research Institute of Electrical Communication, Tohoku University of Japan and his group are pioneering an entirely new sector, in the form of games for the visually impaired. One of the games prototyped by the group lets the player get points by "hitting" virtual locations with a special bat containing a 3D location sensor, based on noises emitted by a fictional creature moving through virtual space. Professor Suzuki explained, "I've heard that there is very little entertainment for the visually impaired, and thought that a game playable by sound alone could be well-received." His group is also developing applications to support the visually impaired, such as systems to train them in estimating object locations based on sound sources.
Hitachi Ltd of Japan, meanwhile, is exploring business use. Yasushi Kanada, senior researcher, Network Systems Research Dept, Central Research Laboratory at Hitachi has prototyped a phone-based conferencing system named Voiscape Prototype II (VP II). The sound locations of multiple users are defined in virtual space, creating an environment identical to that of a discussion with everyone in the same room (Fig 4). The location of a user within the virtual space can be changed with cursor keys or other input from the user terminal. User information used in VP II is implemented through a proprietary extension to the presence information data format (PIDF) defined by the International Engineers Task Force for user information applications. PIDF itself expresses presence information in extensible markup language (XML).
Sound collection technology is likely to develop apace with developments in sound play technology. For example, the number of 5.1-channel digital sound sources is increasing rapidly. Now that DVDs are common, the area covered by digital broadcasting is growing larger, and 5.1-channel sound sources are popping up all around us. This will drive the widespread adoption of playback systems capable of handling 5.1-channel audio, and that in turn will create need for surround recording in home camcorders.
In preparation, Victor of Japan, for example, released the GR-DF570 (called the GR-DF590 in Japan) home-use camcorder in 2005 with surround recording functionality (Fig 5). The microphone normally mounted inside the camcorder was moved into the earphone worn by the user. The technique, termed binaural recording, records sound very close to how it would be captured by a non-directional microphone.
The problem with this approach is that the user is required to wear the earphone. From the viewpoint of usability, it would be preferable to keep the microphone in the camcorder, but camcorders are shrinking rapidly and it is becoming harder to mount microphones internally. A source at Victor of Japan revealed the company is working to overcome the problem, investigating how to best utilize a small microphone to record and play surround acoustics.
by Takahiro, Kikuchi, Satoshi Ookubo
Websites:
Analog Devices: www.analog.com
Apple Computer: www.apple.com
(May 2006 Issue, Nikkei Electronics Asia)
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