|
File Formats Sound Off Make Sense Of The Audio Standards Battling It Out With New Features |
|
|
It was inevitable. There were CDs with songs stored in nearly perfect digital form. There were computers with sound cards, stereo speakers, and CD-ROM drives. Compressed (compacted) file formats made sound files smaller, easier to store, and easier to transmit over the Internet. All the pieces were in place to let audio-loving computer users exchange digital music with or without the record companies?blessing. Understanding the most common audio formats means starting with a few terms. The traditional type of audio file, which you can save to your hard drive or other storage medium, is called a discrete or downloadable file. In general, you need to fully download a discrete audio file, such as a typical MP3, or MPEG-3 (Moving Pictures Expert Group, Audio Layer 3), before you can listen to it using media player software. You can copy many types of discrete files, although there are legal ramifications of duplicating copyrighted material. A streaming file such as those used in RealAudio or QuickTime is a different animal that you can listen to as you download it. Streaming media players buffer, or temporarily store, the incoming data for a few seconds before playing it so that the buffered data will play during the gap and you won notice the problem. The catch is that you may have no easy way to save the complete file on your hard drive. Note that some formats such as MP3 and WMA can be either discrete or streamed, and you can save RealAudio files unless the file maker disabled that option. Streaming files make sense if you don want to waste precious hard drive space on a song you only want to hear once. After all, a song file could take up 2MB to 60MB, depending upon its format. Content providers such as record companies or musicians post songs in streaming formats as a hedge against digital copying, or as a lower-quality preview to encourage you to download a discrete version. Radio stations worldwide offer live programming over the Web using streaming formats such as RealAudio or WMA, but heavy Internet traffic can cause glitches in playback. If this happens, the server may start sending a signal with less data and hence lower quality audio. Streaming files should become more popular as more users get fast cable modems or DSL (digital subscriber line) Internet connections, which can handle larger, higher-quality streaming files. Compression makes audio files more practical to store and send. Audio file compression (called psycho-acoustic compression) generally removes sounds above or below the range of human hearing, or notes that get overed up?by louder sounds. An uncompressed WAV song could take up 50MB, for example, compared to 5MB as a compressed MP3, WMA, or Mjuice (.MJF) file. A few other details affect your choice of audio files. Say youe found a free MP3 song for download that comes in three versions: 96Kbps (kilobits per second), 128Kbps, and 192Kbps. The Kbps part, or bit rate, tells you how much data the file stores for every second of music. The more Kbps, the better the quality, the larger the file, and the longer the download. Users consider 128Kbps to be near CD-quality for MP3s, so if youe happy with a CD fidelity, download that version. Choose the 96Kbps version if you would rather drop some sound quality to fit more songs on your computer and enjoy a faster download. If you have a discriminating ear and lots of storage space, download the 192Kbps MP3. You might run into a few other unfamiliar terms. For instance, you can record WAV files at different quality levels expressed in sample rates (also called frequencies), channels, and bit depth. The sample rate is the number of times per second the original sound was recorded, measured in Hz or KHz. The higher the sample rate, the better the sound, but the larger the file. The number of channels indicates whether the WAV is mono (one-channel) or stereo (two-channel). The bit depth, or resolution, is presented as 8-bit, 16-bit, or even more. It tells you how much information the computer recorded from the original sound in each sample. A 44.1KHz, two-channel, 16-bit WAV file is considered CD-quality.  MP3 These two letters and a digit keep record company executives awake at night. This is because MP3 is a compressed, usually discrete, audio format suited to transmitting high-quality copies of songs online. MP3 files are easy to create and find on the Web, and they pack nearly perfect songs into just a few megabytes. There is currently no practical way for copyright holders to stop unauthorized MP3 distribution of their music. |
|
|
You are not stuck with the file format an audio file comes in. Players such as MusicMatch Jukebox 5.1 convert files among several formats and even rip tracks from CDs. |
|
|
The MP3 format typically compresses songs at ratios of about 10:1, 17:1, or even 70:1. It can record at a bit rate of 64Kbps or lower to conserve space or as high as 320Kbps for utmost quality. We used MusicMatch Jukebox 5.1 to encode a three-minute song into a 2.82MB MP3 file at 128Kbps. We used the default CBR (constant bit rate) technique, which samples the song at a steady rate. The VBR (variable bit rate) setting samples more times during usy?parts of the song for better quality, but the resulting MP3 file might not work in every player. Our VBR MP3 took up 2.9MB, with the VBR level set to about the same quality level as our CBR file. Windows Media Audio Microsoft Windows Media Audio 7 (.WMA files) is a compressed, discrete, or streaming format designed to be a secure alternative to MP3. WMA chief advantage over MP3 is that it sounds better at lower sampling rates, according to Sean Alexander, a Microsoft technical product manager. An April 1999 NSTL comparison (http://www.nstl.com) commissioned by Microsoft found that 51% of listeners thought songs recorded in an older version of WMA at 64Kbps sounded more like the original songs than when recorded as MP3 files at 128Kbps (which received 29% of the vote, with 19% undecided). Alexander says that the latest WMA files (version 7) sound even better. This means that a track can be recorded to a smaller file, such as a 1.43MB 64Kbps WMA edition of our three-minute song, without noticeable fidelity loss. You can record WMA files from 5Kbps at 8KHz quality to 192Kbps at 44MHz. |
|
|
RealJukebox 2 is one of several versatile media players. It lets you tune into Web radio stations, burn CDs, and listen to a variety of file formats. |
|
|
WMA other advantage is that content providers can copy-protect it through DRM (digital rights management) schemes such as Windows Media Rights Manager 7. You can download and play a WMA file, but if it protected, you must perform an additional step. For example, your browser might connect to another site to download a file called a license. This license may be free or cost a few bucks, and may only unlock the song for a certain amount of time or number of plays. Many consumers consider this a hassle, but Microsoft and other members of the SDMI (Secure Digital Music Initiative) consider protected music the future. One of many sites carrying WMA files is http://www.musicblitz.com.WAV Microsoft common WAV format has very high sound quality but captures audio in a discrete file without compression, which means one minute of audio takes about 10MB of storage. MusicMatch Jukebox turned our three-minute song into a 31.08MB WAV file at CD-quality (44.1KHz, stereo, 16-bit) settings. WAV files are not copy-protected, so only their sheer size will keep you from distributing songs in this format. Still, they work well for the short ings?and sound effects you can assign to Windows error messages, or for temporarily storing songs on your hard drive before you burn them to CD-R (compact disc-recordable). You can download WAVs from sites such as http://www.wavplace.com. Apple AIFF (Audio Interchange File Format) and the AU format, originally developed for Unix, are very similar to WAV. Although the formats aren interchangeable, many media players can play all three. RealAudio RealNetworks is the biggest name in streaming media and has a bewildering array of file formats, such as RA (RealAudio), RM (RealMedia, RealAudio G2), RMX (RealAudio Secured), and many more. Most sites simply call such files eal.?If your RealPlayer software can handle the format, it will prompt you to download a free upgrade. Many music sites such as http://www.emusic.com offer previews of songs in a Real format. |
|
|
In audio files, size matters. Windows Media promises better sound than MP3 from smaller files, and RealNetworks is replacing the G2 format with the more bandwidth-friendly RealAudio 8. |
|
|
RealAudio chief drawback is that most users still have 56Kbps or slower modems, so typical playback isn the highest quality. Download sites sometimes let you choose the best Real file for your modem speed. Record companies and musicians can encode their streaming or discrete music files in Liquid Audio secure LQT (Liquid Track) format and then let the company sell the songs on more than 800 sites such as Amazon.com (http://www.amazon.com). Consumers can download tracks for free or a dollar or two each and listen to them on the free Liquid Player 5 ( http://www.liquidaudio.com), which can burn many Liquid Tracks to CD-Rs playable in all modern CD players. You can even play your Liquid Audio files on different computers with a special assport?file. LQT files are compressed, yet bigger than MP3s because of security features. However, they offer CD-quality audio and sometimes liner notes, album art, or lyrics you can view while listening. MIDI The MID discrete file format descended from MIDI (Musical Instrument Digital Interface), which lets digital synthesizers and other devices exchange data. A MID file is not an audio recording, but instructions telling a sound card how to reproduce the music. This lets a MID file store a minute of music in about 5-10KB. Today, MID files are mainly used for original instrumental works, amateur renditions of popular songs, and soundtracks to games and online greeting cards. Major upgrades to MIDI in the last few years mean it no longer needs to sound so much like the soundtrack from the movie ron.?The DLS (Downloadable Sounds) 1 and 2 formats include samples of real instruments to help sound cards reproduce audio more correctly. Look for .MID files at http://www.midi.net. Optical Disc Formats Today optical discs such as DVD (digital versatile disc) can store huge amounts of information, letting them store audio with lower bass, higher treble, and more channels (separate audio signals beyond eft?and ight? for surround sound applications. Youe probably most familiar with the Red Book format, even if unknowingly. That the 16-bit, 44.1KHz format also known as CD-DA (Digital Audio) that used on music CDs. HDCD (high-definition compatible digital) extends the bit depth to 20-bit on compatible players. SACD (Super Audio CD), meanwhile, takes 1-bit samples at a huge sampling rate of 2.822MHz (megahertz). The much-delayed DVD-Audio standard handles five channels of 24-bit, 96KHz sound for movie surround sound, or regular stereo with two 24-bit, 192KHz channels. A Final Note Other contenders are claiming to beat MP3 quality, security, or file size. Sony ATRAC3 (Adaptive Transform Acoustic Coding 3) is a compressed, discrete format used in the Sony Memory Stick Walkman. Mjuice is an encrypted, compressed format that can have controls such as a built-in expiration date. AT&T proprietary, compressed .A2B format also yields secure files with copy protection. Besides DRM features, another trend in audio formats is extra content, shown in all the goodies the bluematter format can contain. Time will tell whether digital audiophiles will embrace the added value in such secure formats over the freewheeling nature of MP3s. 
by Marty Sems |
|
|
Put Your Files In Play It can be tough to choose the right media player from all the powerful, free players you can download. Although most players accept plug-ins, or optional software for supporting more formats, youl probably need more than one media player to hear every type of file. Some players, such as MusicMatch Jukebox 5.1 (http://www.musicmatch.com), can also rip files from CD, encode them in MP3 or WMA formats, and burn MP3s or WAVs to CD-R (compact disc-recordable). The free version of MusicMatch Jukebox supports unlimited recording at up to 320Kbps (kilobits per second). RealJukebox 2 Basic is available for free on RealNetworks?site (http://www.real.com). Version 2 of this encoder/player lets you burn CDs, tune into Webcasting radio stations, and play MP3, Mjuice (.MJF), and Liquid Audio (.LQT) files. Apple QuickTime (http://www.apple.com/quicktime) is a one-stop shop for multimedia playback. QuickTime Basic 4.1.2 plays discrete and streaming formats such as MP3, WAV, and AIFF (Audio Interchange File Format), plus video formats. Windows Media Player 7 (http://www.microsoft.com/windows/windowsmedia) adds CD burning, support for skins (different looks for the player), and a file transfer feature for portable player devices. It also plays radio Webcasts, streaming Windows Media audio and video, and formats such as MP3, WMA, and AIFF. If you rather carry your media player around, check out devices such as Creative Labs?new 6GB Nomad Jukebox ($499) or the Soundsgood MP3 player module ($269) for the Handspring Visor handheld computer. Meanwhile, Iomega new HipZip player ($299) uses 40MB PocketZip (formerly called Clik!) disks instead of the flash memory in most player devices. Be sure to check the formats any device can play before you buy, and try to get the most storage you can afford. |
|
|
|
