Number 240 - May 2003

Digital Sound A Grownup's Guide to Audio Files
By Susan Ives, PC Alamode Magazine
I must have been in junior high school when I bullied my father into buying me a transistor radio. He was a pioneer in the early days of radio and stomped around the house muttering that unless you knew how to build a radio yourself out of a coil of wire and an oatmeal box you had no business listening to one. For him it was all about the technology. For me it was about the music.    It's still about the music but the technology is rearing its ugly head again. All I had to do to listen to my transistor was slap in a 9-volt battery and tune into my favorite station. After more than 30 years of progress, I'm having to learn how to build the radio. It's a digital radio, made of bits and bytes, but it's a whole lot more complicated than turning that analog dial. ANALOG/DIGITAL:    To get the gist of digital sound it helps appreciate what came before - analog sound. Physicists can probably give you a concise definition, but for non-scientists who took their last physics classes when dinosaurs ruled the earth, here's how I see it. Analog is physical. In the analog world, something really happens. The gears turn and your analog watch ticks over another minute. The needle bumps up and down on the grooves of a vinyl disk and sound waves reverberate. Digital is made up of digits, ones and zeros, which represent on and off. Since there are two options, they are called binary digits, or bits. A group of 8 bits is a byte. A megabyte (MB) is 1,048,576 bytes.    On my ancient transistor radio my only choices were between AM and FM, between WIP and WMMR. Now it's more complicated. Digital audio files come in a variety of formats. Within those formats they may be available at different quality levels to accommodate fast and slow Internet download speeds. Depending on the type of file I select I may need to decide to use a particular media player that recognizes that file format. I can download the audio files for later listening, or stream them, listening to them on the fly. My old transistor came in a brown leather case. Now, I can even download skins on my software media players, changing the way they look with the click of a mouse.    By far, the most popular format for listening to music is MP3. Young people know all about this. Oldies like me had to learn it. MPEG (pronounced EM-peg) stands for Moving Picture Experts Group. MPEG contains both video and audio data. DVD movies use MPEG for their video compression. The audio is encoded in... MP3 which stands for MPEG-1 Audio Layer-3. MP3 is a compression algorithm. An algorithm is a procedure or a formula for solving a problem. (The word has nothing to do with rhythm, so get that out of your head. The term comes from the name of a mathematician, Mohammed ibn-Musa Al-Khowarizmi, who lived in Baghdad in the 9th Century or thereabouts.)    Back to MP3. The compression algorithm works by discarding high and low frequency sounds that only cockroaches can hear. There are different levels of MP3 compression. 128 bit and above compression gets almost CD-like quality. MP3 compression reduces the file size to about 10% of the original or even smaller.    Most MP3 files are made from audio CDs, sometimes in violation of copyright laws. Audio files are extracted from a CD and put on a computer's hard drive using software called a Ripper and then converted to MP3 format using another piece of software called an Encoder. Ripping is also called DAE (Digital Audio Extraction). A Ripper will convert a music CD's files, which are in a .CDA format into a .WAV file. Dale Swafford offers a six hour course on making music CDs, so don't expect me to go into detail. Just toss around the terms ripper and encoder and you'll look like you know what you're talking about.    People share MP3 files over the Internet. This is the main reason why the copyright controversy has arisen. P2P (Peer-to-Peer) Networking, is the technology used by Napster, Grokster, KaZaA and file sharing sites. In a nutshell, their software enables users to search the hard drives other people around the world who use the same program. Users can designate which files are open to the outside and allow people to download them. Although music sharing P2P operates over the Internet, P2P is different than the client-server model used by the Internet.    There are also MP3 files that you can purchase for a small sum, or download for free. Most free MP3s are delivered at 24kbps - not CD quality, but they sound pretty good to me when played on my computer's sound system. Legal free MP3s are usually played by obscure artists. Try out mp3.com to get a feel for what's available. I'm streaming (playing right off the Internet, not downloading) a collection of Celtic songs from MP3.com as I'm writing this article.	So how do you play the darn things? Obviously, you can play them on your PC. If you have a computer with Windows 98 or above, you probably have the Windows Media Player (http://www.microsoft.com/windows/windowsmedia/) already installed, or you can download something like the RealPlayer (http://www.real.com) Some of these players are called jukeboxes, which typically means that they can handle several different file formats and organize audio files into playlists, or user-constructed sequences of songs. Nobody--but nobody--plays an entire album any more. The new best thing is individually crafted compilations. One well-known jukebox is MusicMatch (http://www.musicmatch.com).    There are also portable MP3 listening devices, ranging in price from about $100 to a whopping $500+ for the Creative Labs Nomad Jukebox with 40GB of memory. You can either download music, or rip and encode your own audio CDs. No more carrying around your originals, worrying about them getting scratched, misplaced or stolen. MP3 players are rugged and virtually skip-proof. Depending on the memory size, they can play hundreds of hours of music. If you download your MP3s from the Internet, you can also burn them onto CDs and play them on your regular stereo system or boom box. MP3 has been around for a while and it has competition.    Microsoft has come up with a competing file format, WMA (Windows Media Audio), which claims to produce a higher quality file at half the size of MP3. Ogg Vorbis is a patent-free compression technology, comparable to WMA and MP3.    Streaming Media is media that comes to you in chunks, called packets, rather than making you wait until an entire file downloads. It is mainly used over the Internet. A little bit of the file downloads, is put in a buffer, or holding area, then starts playing. While you're listening (or watching; this works for video as well) the next packet is already downloading and poising itself in the buffer. With streaming media you can start listening to a large file right way without waiting for the whole thing to download. Real Networks (http://www.real.com) was in the forefront with this; their files have an extension of .RA WMA files can also stream. Many radio programs are streamed - I often listen to shows I missed on NPR at (www.npr.org). They stream in Real Audio, Windows Media Audio and Apple QuickTime.    Some of the older formats are still alive and well.    MIDI (Musical Instrument Digital Interface) was designed to record and play back music on digital synthesizers, such as an electronic keyboard. The sounds in a MIDI file are actually embedded in the sound card, so the quality of a MIDI file depends totally on the quality of the sound card. 32 different instruments, actual sound samples, can be replicated by the wavetables on soundcards and can be combined and shuffled to sound like 128 instruments - an entire orchestra in a chip!    MIDI files are considered old-fashioned: they sound synthesized, rely on the quality of the soundcard and can't replicate human vocals. You'll find them used as backgrounds to Web sites, in karaoke files (the .kar format is a variation of a MIDI) and, of course, in piano bars too cheap to spring for a baby grand. MIDI files do have the advantage of being small files because they are just sending instructions to the sound card.    WAVE audio file format was created by Microsoft. Wave files - identified by a file extension of .WAV, are used for everything from computer system sounds (You've Got Mail is a Wave file) to the sounds on computer games and CD-quality audio.    Most WAV files use PCM (Pulse Code Modulation), a generic digital way of transmitting analog information. PCM is also used in audio CDs and DAT (Digital Audio Tapes). PCM files can be compressed using DPCM, or Differential Pulse Code Modulation. Rather than recording all the 1 and 0s, DPCM just records differences between consecutive samples. APCM (Adaptive Differential Pulse Code Modulation) analyzes a succession of samples and predicting the value of the next sample. DPCM and APCM are LOSSY formats, which means that they compress data by removing some of it, usually redundant information. You probably won't notice the missing data, but the file can't be returned to its exact former state after undergoing lossy compression. My father is probably chuckling from the grave. After all these years, I'm learning how to build the radio.    Copyright PC Alamode Magazine, Alamo-PC
Number 240 - May 2003