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Volume 35 (Mar 04, 2005)
Reproducing realistic sound: Melody LSI chip for mobile phones
The parallel histories of mobile phones and ring tones
Mobile phones are now used in every business and social setting imaginable, and we therefore often hear ring tones alerting users to incoming calls and text messages. Ring tones were originally intended to provide mobile phone users with a way to easily distinguish between the ringing of their own phones and those of others. At first, these tones were either monophonic rings with variations in tone length or simple melodies with tone intervals. Along with the advancement of mobile phones came the introduction of sound effects and melodies using polyphonic tones. The evolution of ring tones was further accelerated thanks to the widespread acceptance of Chaku-melo™ (ring tone melodies) by Japan's youth, who began to access mobile-phone web sites to download the latest hits and songs from the past to use as ring tone melodies for their phones. In addition to the 64 mainstream polyphonic tones, Chaku-uta® (ring tone songs that are used instead of melodies to indicate incoming calls and text messages) have arrived on the scene. Ring tones are no longer used to simply alert users of incoming calls or text messages, but also to provide an element of entertainment that mirrors the interests and personalities of users (Figure 1).
During this evolution of ring tones, the functions required of LSI chips have been undergoing a transformation of their own. For polyphonic and other ring tone melodies, the generation and playback of music is carried out using the musical instrument digital interface (MIDI), a format with which musical composition data that matches an original musical score is employed to create and play instrumental sound. For Chaku-uta®, however, audio compression and extension technologies such as MP3 and AAC (both of which produce higher sound quality than MIDI) are used for the playback of music data. Thus, it became necessary for melody LSI chip to be capable of reproducing sound using the conventional MIDI format, and also to incorporate a function that would make it possible to expand and play compressed music data in formats such as MP3 and AAC.
Using the 陲鳳D9993 chip to reproduce realistic sound
To meet its customers' ever-changing mobile needs, including those resulting from the introduction of Chaku-uta®, NEC Electronics launched sales of the µPD9993 melody LSI chip (Photo 1). The µPD9993 became the industry's first* LSI device to provide playback support for audio compression technologies such as MP3 and AAC.
It is unnecessary to incorporate a separate LSI chip for MP3 or AAC playback with the µPD9993 melody LSI chip because it enables the playback of audio stored in memory or of downloaded music with sound that is both realistic and comparable to that of a CD in terms of quality (Figure 2).
The µPD9993 chip also comes with a 3D surround sound function, and the adoption of Adaptive Surround™ technology makes it possible to produce expansive sound comparable to that generated with five channels from a two-channel stereo sound generator source. Moreover, DVX™ technology realizes a stereo surround sound effect that makes it sound as if there are five channels even when only twin speakers are used (Figure 3).
Providing mobile phone solutions to our customers
No longer used for merely making phone calls and text messaging, mobile phones are now fast becoming multimedia terminals that incorporate functions enabling users to enjoy games, listen to music and record/playback video footage. To meet the needs of its customers, NEC Electronics successfully completed its development of a melody LSI chip for mobile phones. Since the µPD9993 chip not only supports MP3 and AAC formats but is also equipped with a surround sound function, users can enjoy conventional ring tones, games, music and video footage with sound that is both realistic and brimming with presence. We at NEC Electronics will continue to dedicate ourselves to providing solutions that will make mobile phones even more sophisticated and multifunctional.
* As of September 21, 2004
•"Chaku-melo™" is a trademark of Astel Tokyo (Yozan Inc.), Futabasha Publishers Ltd., etc.
•"Chaku-uta®" and "Chaku-uta full™" are trademarks or registered trademarks of Sony Music Entertainment Inc.
•DiMAGIC Virtualizer X™ (DVX™) and Adaptive Surround™ are trademarks of DiMAGIC CO., LTD.
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