Must read article with quote from Norbert Deberko, VP of Engineering at EDIG.
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Portable Players? Audio
Decoder Uses DSP, MCU
Portable music players that store musical content on flash EEPROM remain hot items for development, but designers are switching from using custom chips to already available DSPs and microcontrollers.
Major manufacturers of digital signal processors (DSP) and audio integrated circuits (IC) are beginning to announce product plans for portable music players. These devices are a new class of portable audio player that store music content in flash electrically-erasable programmable read-only memory (EEPROM).
The DSP cores used in mobile phones, and the microcontrollers that serve as central processing units (CPU) in personal digital assistants (PDA), are now being applied as audio decoding chips. Until now, music players have generally used custom decoders to handle the Moving Picture Coding Experts Group Phase-1 (MPEG-1) Audio Layer III (MP3) coding scheme. This situation is fast changing.
Behind the change is the increasing diversity of plans for portable player products. All of the portable players on the market thus far have been capable only of playing musical content encoded with MP3. This is also changing with the entry into the market of a host of new companies (Fig 1).
The next generation of equipment, which will begin to appear towards the end of 1999, will be more than just play-only systems. New fusions of PDAs as well as mobile phones are coming into existence as the portable player evolves from its conventional audio equipment role as a dedicated music player.
The Fusion Begins
Two directions have been taken in the planning of portable players scheduled for 2000 and beyond (Fig 2). The first leads to the play-only portable unit, with the stress on small size, light weight, and thinness. Products range in size from that of a postage stamp to a credit card, with weights below 50g. The Pocket Digital Audio, a portable MP3 player, released in June 1999 by venture business Dynamic Naked Audio, Inc of Japan, is one of the first of the new breed. It measures only 53mm x 46mm x 16mm, with a footprint that is about half the size of a business card. It weighs only 30g.
The second design plan being pursued is the development of multi-function players that not only have audio functions, but also communication and information functions. Plans in this area see a union with existing products such as mobile phones, PDAs, e-mail terminals and navigation systems. ?In the future, users are going to want portable players with a selection of extra functions,? predicted Micah Stroud, brand manager, Sound Card Creative Labs, Inc of the US.
Casio Computer Co, Ltd of Japan released the Cassiopeia E-500 PDA, which features MP3 decoding functions, in March 1999. Apparently, a number of mobile phone manufacturers are also quite interested in audio play functions. As a source at the Audio Division of Sharp Corp commented, ?It would be a lot simpler to just carry one piece of equipment outside the office or the home. If music distribution service through mobile phones takes hold, there should be considerable need for this.?
Even in Japan, MP3 players are gradually expanding their user group to encompass personal computer (PC) owners. ?We are selling a few models steadily at the rate of 50 or 60 units a month, and prices are solid,? revealed a salesperson from a major home appliance outlet in Japan. Portable player development projects are still increasing in the industry. Last year there were only a few firms developing products for the emerging market, but there has been a sharp rise in these numbers over the last six months. Major manufacturers have joined venture businesses in jumping onto the bandwagon, with over 20 firms worldwide having already announced development projects. If product development efforts result in units that are small and multi-function, then portable players will be sought, not only by PC users, but by the general consumer.
Move to Off-the-Shelf Components
As product planning diversifies, the audio decoding that makes up the core of portable players is beginning to be handled by general-purpose DSPs and microcontrollers, instead of the traditional custom ICs with custom algorithms.
All of the MP3 players on the market currently use MP3 decoder ICs, and most of those are made either by Micronas Intermetall GmbH of Germany or STMicroelectronics NV (a joint venture between France and Italy). These custom ICs usually offer two key advantages ? low dissipation and low price. They are an ideal solution to demand for smaller products with longer, continuous play times.
When the goal is to provide multi-function performance, however, the situation is different. Thus, when portable players that combine mobile phone and PDA functions are considered, it clearly makes sense to use the same microcontrollers and DSPs already used in those products. ?A custom chip can be 20% lower in cost, for audio equipment applications,? explained Gary Johnson, worldwide audio business manager, DSP Emerging Markets Group, Texas Instruments (TI) Inc. ?For audio applications, they are clearly the best choice. When you combine their function with information devices, however, using a single IC to implement a range of functions should provide lower product costs.? His attitude is becoming more common, along with the call of IC manufacturers for the increased use of general-purpose ICs.
The processing performance needed for audio decoding, according to system architect Dave Sparks of Creative Labs, is ?about 30 MIPS (million instructions per second) for MP3 decoding itself, and about 50 MIPS with acoustic processing thrown in.? The Casio Computer portable information device handles MP3 decoding with the VR4121 reduced instruction-set computer (RISC) microprocessor (131MHz clock) from NEC Corp. For advanced audio coding (AAC), which represents the heaviest processing load for portable player decoding, most in the industry consider that about 80 MIPS is required. A single decoding program runs between 10 and 30 Kbytes.
Middleware Makers Appear
In response to these developing trends, major IC and audio IC manufacturers are announcing strategies based on the use of general-purpose cores in portable players (Table 1). They are developing firmware for audio decoding by general-purpose cores, directly targeting portable player applications.
TI, for example, announced the TSM320C5409 16-bit fixed-point DSP in May 1999, which boasts 80 MIPS at under 60mW dissipation. This was the latest version of the firm?s DSP core, originally targeted at the mobile phone market.
Cirrus Logic, Inc of the US began sample-shipping the EP7209 for portable players, single-chipping a liquid crystal panel controller and a flash EEPROM interface. The ARM720T from ARM Ltd of the UK, a 32-bit microcontroller, serves as the audio processor core.
Motorola, Inc also plans to commercially produce a low-power version of its 24-bit fixed-point DSP around the spring of 2000. The firm is aiming at the portable player market, having previously shipped DSPs that cater for the high-end audio equipment market.
Venture businesses are appearing, too, to develop the middleware for the portable players using these new chips. One such firm is e.Digital Corp of the US, which offers the MicroOS middleware that implements power management, user interface management, and flash EEPROM musical content and voice file management. According to Norbert Deberko, vice president of engineering, ?We want to make development easier for equipment manufacturers, and help them get their products out as quickly as possible.?
Diverse Encoding System Use
Multi-function performance is not the only reason why portable player manufacturers are beginning to switch to general-purpose ICs. Another major reason is the diversity of audio encoding schemes and copyright management technologies used for musical content.
Until now, the record companies have sold music content in a single data format, but this situation is changing rapidly, especially in the area of Internet-based music distribution. Each record company will now choose the data format that best fits its specific service.
In addition to a host of different audio encoding schemes, it now seems likely that a variety of copyright protection technologies will also be put into use. The Portable Device Working Group (PDWG) within the Secure Digital Music Initiative (SDMI), which is investigating possible copyright protection technologies for portable players, does not plan to standardize a single technology. Instead the group will probably just add information to identify the encoding scheme used for music content, and which copyright protection technology has been used (Fig 3).
Music distribution is viewed by many equipment manufacturers as the key application for portable players. If record companies adopt a range of methods, then equipment manufacturers will have no choice but to support them all. Even if the portable player itself does not support them, it would also be possible to (1) convert the data on a personal computer (PC), or (2) select one of several schemes when purchasing the music content. The problem with alternative (1) is that it takes time, and would probably degrade fidelity, while (2) would require retailers to stock multiple versions of every tune. Neither is viewed as a very acceptable solution. Most manufacturers now shipping MP3 players agree that in the future they will probably have to support multiple schemes.
Some manufacturers have already announced portable players that support multiple audio encoding formats. Thomson Multimedia SA of France, for example, will ship its LYRA portable player in the third quarter of 1999, which will support MP3 and the RealAudio technology developed by RealNetworks, Inc of the US. A function will be provided to enable new decoding software to be downloaded via a PC.
Kobe Steel, Ltd of Japan will also offer a player that supports multiple encoding schemes. The Solid Audio player, shipped in July 1999, was originally specified to support only the TwinVQ encoding scheme developed by NTT Corp of Japan. However, according to Kobe Steel, ?We decided to plan for the future, and made the system capable of installing both MP3 and AAC software via miniature memory cards.?
Manufacturers Choice
The decision to use general-purpose or custom ICs will depend on whether manufacturers place emphasis on lower production cost or the faster development of players supporting multiple encoding schemes.
IC manufacturers that now ship MP3 decoders will provide support not only for MP3, but a range of other encoding schemes as well. Once the encoding scheme is settled upon, a custom IC can be used to significantly reduce equipment development time and effort. There is not yet a wide selection of audio decoding software available for general-purpose ICs, and when the time required for an equipment manufacturer to develop this firmware is considered, custom ICs become an attractive option to firms entering the market. As Dynamic Naked Audio commented, ?We made our equipment using an MP3 decoder. To be honest about it, it was the only choice we had at the time.?
Richard Fleischman, senior marketing director at Liquid Audio Inc, however, stressed, ?As encoding schemes and copyright protection technologies evolve, new data formats will continue to appear. I don?t think it will be easy to converge on a single approach in the future, either.? It is quite possible that companies waiting for custom ICs will be unable to keep up with the pace of technical progress.
Both Thomson and Kobe Steel, for example, use 16-bit fixed-point DSPs for audio decoding. There was not a custom IC capable of handling both TwinVQ and RealAudio decoding. Rather than wait for one to appear on the market, or develop one in-house, these firms decided that selecting a general-purpose part would get their products out the door more quickly.
by Fumitada Takahashi
and Tarou Yoshio
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