This series of articles will provide an overview of current audio usage and devices within the cellular handset, as well as information on the direction of future audio architectures within cellular handsets.

The Evolution of the Cell Phone
The basic purpose of a cellular handset is for voice communication between the caller and the receiver. However, consumers now use the phone for recording messages, playing games, e-mailing photographs and sending text messages, calculating expenses, taking still pictures and video, playing video clips and movie trailers, listening to MP3 files, listening to FM radio, or watching terrestrial or digital wideband broadcast TV, and storing addresses and phone numbers, with more to come.

In the first half of 2004, Americans spent 97% of their cell phone charges for talking. Talking may soon be the least used feature of a cell phone.

An array of new services will alter the way we use our cell phones. We'll be able to tune in to as many as 100 channels of TV, get GPS directions to anywhere, and view and pay for a wide variety of products.

Informa Telecoms and Media reported in July 2005 that music, gambling, games and adult content will help create a $42.8B market globally by 2010. Emerging new markets such as mobile TV, user generated services and personalization (graphics and visual themes) are forecast to contribute a further $11B in revenues.

Revenue models are either purely per event based or are combinations of subscription charge and event based charging structures.

CURRENT AUDIO USAGE IN CELLULAR HANDSETS
Overall worldwide mobile phone sales will increase 16 percent in 2005 to 779M and will reach the 1B unit milestone in 2009, according to a market study by market research firm Gartner. The Gartner study said next-generation phones were the largest growing segment and predicts that more than 100M 3G phones will be sold next year and more than 200M smart phones will be sold in 2008. In 2009, over 2.6B units are expected be in operation worldwide.

Mobile phones are becoming the most common consumer electronics information device ever made.

CELLULAR HANDSET APPLICATIONS REQUIRING AUDIO COMMUNICATION
The basic purpose of a cellular handset is for voice communication. Associated with the voice call is generating the voice side tone signal. Additional voice related functions include Voice Commands for phone functions (requiring Voice Recognition software), voice annotation of photos, narration of video, and voice messages. Still another audio function is the familiar sound you hear when depressing any keys (feedback to the user that the key depression has been recognized), or making menu selections.

RING SOUNDS (RINGTONES)
An obvious and simple use of audio in a cellular handset is for ring sounds. But ring sounds these days are anything but simple:

RECENT HEADLINE
Ringtones make sweet music for record labels Monday, June 27, 2005; Posted: 9:50 a.m. EDT (13:50 GMT)

WASHINGTON (Reuters) -- Ringtones, those song snippets that announce incoming mobile-phone calls, are now making noise at the top of the pop charts and on the bottom line of multibillion-dollar businesses.

Ring Sounds are among the fastest growing types of mobile content, and ring sounds sales is a very lucrative business for the artists, music publishers, and record labels. A 20-second ring sound can sell for as much as $2, while a single full length (average 3 minutes) song track from Internet download services sell for around $0.99 cents per song.

That is a value factor improvement of 2x in price for 1/9 the content, giving an effective 18x increase in overall value for the ring sound as compared to the song from which it may be derived. Cellular operators are actively concluding deals for ring tones by working directly with the artist, or with music labels and publishers to provide ring tones of popular music. Often, the derived ring sound from a major artist's song will outsell the original song, both in numbers of downloads and in revenue.

Ring tones are topping the popular music charts. "Crazy Frog" (and all its zany variations), is one of the most popular "ring sounds" on the market today. In the United Kingdom, a song inspired by "Crazy Frog" kept major artist's songs OFF the top singles chart spot for several weeks.

The ring sound business is so lucrative that piracy has risen to significant levels. Research suggests that Ringtone Piracy (by various means) has cost an estimated $40 million since the beginning of 2004, with damage estimates reaching $123 million by 2007. The performing-rights organization ASCAP (American Society of Composers, Authors and Publishers), which collects royalties for songwriters and song publishers, says the $5 million it will collect from ring sounds this year already matches revenue from Internet radio, online greeting cards and other "new media" combined. That does not count revenues collected by BMI (Broadcast Music, Inc.), another similar major organizations.

So the business is not likely to fade away anytime soon. A new version of ring sounds, called Master Tones, Voice Ring Tones, True Tones, Real Tones, or "Dead Ringers" (slang, for being an exact copy), now use actual pieces of complete music recordings, including lyrics and all musical accompaniment. The audio is in MP3, WMA, or AMR digital format that can be used as a ring sound on many newly released phones, which is generally played back through a software based media player program.

The report from Informa Telecoms and Media predicts that by 2010, sales of real tones will be worth nearly $6.8B, driven in part by the increasing downloads of popular digital music to MP3 players.

CALLER RING BACK TONES (CRBT, "Color Ring Back Tones", Cai-Ling)
The CRBT service is commonly called "Color" Ring Back Tones, based on a transliteration of the word "Caller" and also of the Chinese name for the service, "Cai-Ling", where the service has enjoyed enormous popularity and growth. IDC anticipates 60M U.S. wireless subscribers will use CRBT's by 2009, further driving up operator revenue growth and average revenue per user (ARPU).

What is a Caller Ring Back Tone? It is the ringing (or "ring-ring" sound) you hear when placing a phone call, which is just a sound effect to reassure you that the connection is going through. There's no real reason for it to be the "ring-ring" sound. It can be whatever the telephone network allows it to be.

The CRBT service is a personalization option. Subscribers customize the CRBT from a wide selection of commercial music, personalized messages, celebrity greetings, or voice announcements to replace the monotonous ring connecting tone that the caller would ordinarily hear.

Unlike normal ring sounds, CRBT sounds and music reside on the network so they can be used with any mobile phone and sound similar to an AM radio. Consequently, network operators have latched onto CRBT as another source of revenue: the operator controls the CRBT. The effective quality of the CRBT to the listener is obviously dependent upon the original audio recording/composition quality, but also depends upon the audio signal path in the cell phone. The signal is in the voice communications path, and is fundamentally 3dB "half-power" point bandwidth limited by the telephone network to frequencies between 300Hz and 3.5KHz.

3D Ring Sounds
Hardware synthesizers used for ring sounds, and software media playback software are beginning to offer Stereo Enhanced (commonly called "3D Sound) options for the music generated.

3D ring sounds are ring sounds that (1) have the stereo enhancement algorithm rendered by the playback engine based upon pre-placed commands in the ring sound digital audio file, (2) have true Head Related Transfer Function (HRTF) spatialization in the 3D space around the head based on algorithms executed according to commands in the ring sound digital file, or (3) are standard Stereo ring sounds which are operated upon by a stereo enhancement algorithm contained as part of (a) an analog amplifier system, (b) HW or SW synthesizer, or (c) other audio software program.

Option (2) works with any Stereo music to a greater or lesser degree depending upon the algorithm and the musical content, and does not require any "programming" of the basic music used.

Another form of "3D" ring sounds exists where the stereo enhancement or true 3D sound spatialization is a built-in part of the music composition process. In that case, no rendering of the effect is done on the cell phone. Only a stereo amplifier is needed to hear the spatialization effects. These are typically provided as standard MP3 audio files.

Music
The new report from Informa Telecoms and Media predicts that by 2010, mobile music sales will be $11.3B, of which, about $4.5B will be for music tracks.

Music is a strong and compelling segment of the non-voice revenue stream for wireless operators. For music fans to buy mobile music, it's got to be easy and convenient. Therefore, cell phone makers and operators are creating alliances with popular music download services to bring those services to cell phone consumers since those services handle Digital Rights Management (DRM) issues with the artists, publishers, and labels. Fortunately, MP3 players and companion downloadable music services have enabled a positive customer experience for paying for and downloading music.

The standalone MP3 market has been forecast to grow dramatically in the next few years, estimating that consumers will buy more than 104M units by 2009, up from between 28M " 35M units shipped in 2004. Cell phone annual unit sales, (currently estimated at 780M units in 2005) outnumber MP3 player unit sales (estimated at 50M units in 2005) by a factor of about 15:1. Some cell phones are now capable of being called "MP3 players", and the proliferation of models from suppliers is increasing rapidly " so fast that by 2008-2009, they will be the predominant MP3 playback device.

The mobile phone is becoming a credible music playback device. But it does not yet meet standalone music player versatility and audio performance specifications.

Why?
Audio performance specifications are part of the answer. The cell phone is an electrically noisy environment and is not getting any less so over time. Achieving high quality consumer level noise floor, PSRR, audio bandwidth, and output power specifications is much harder to do in a cell phone as compared to a standalone portable music player.

Audio format standards are also part of the answer. The vast array of audio standards can create confusion among consumers. Which standards? Here is a partial list: MP1, MP2, MP2.5 layer 3, MP3 (8 to 320 Kbps), MP3 VBR, AAC (8 to 320Kbps), Audible (formats 2, 3, and 4), WAV AAC (16 to 320 Kbps), AIFF, WMA, WMA-DRM, Ogg-Vorbis, ASF, RA (RealAudio), and Protected AAC (from iTunes Music Store, M4A, M4B, M4P), and Apple Lossless

The defacto industry standard for mobile digital audio files is MP3.

MP3 is clearly the major format on cellular phones.

MP3 is clearly the major format on standalone players as well. But standalone MP3 players properly playback many more other digital audio formats than cell phones. Files downloaded for these MP3 players can typically also be played on other playback devices. Multiple formats allow for downloaded music to be played on several platforms " pay once, play anywhere.

MP3 is clearly the format for the vast majority of digital music currently available. But other formats have advantages such as little or no license fees, smaller file sizes, and increased perceptual clarity. Content quantity in these newer formats is expected to increase over time.

MP3 is the current choice for near-CD quality digital audio. However, AAC is its designated successor as it is able to provide the same sound quality with a larger compression rate. In addition it enables higher quality encoding and playback for high definition audio (at 96 KHz sampling rate). So AAC is the most promising candidate e.g. for new portable playback devices using solid state memory. The effective data rates will be below 48 Khz sample rate.

Handset manufacturers and operators are devoting significant energy into creating sophisticated music devices with advanced music download, storage, and format support features, as they and the operators believe the cell phone will be the player of choice for mobile music.

The music playback quality and capability of the cell phone will have to approach that of the standalone MP3 player. In addition, the industry target for playback time on a cell phone (currently about 30 hours) is approaching 100 hours, requiring more efficient audio devices and longer life batteries.

Next Week: Gaming on your phone

Kenneth Boyce is the Staff Strategic Technologist for National Semiconductor's Audio products group. Prior to joining National, Boyce served as director of the Audio and Communications Division at Oak Technology. He holds a bachelor of science degree in electronics from West Virginia University.