Get the lowdown on common digital-audio fallacies.

by Dan Phillips
   The Information Age is a wonderful time, isn’t it? With global media and the Internet, you can find data on just about any topic. Unfortunately, a lot of conflicting information is floating around out there, and it’s often hard to tell fact from fiction. This article attempts to clear the air by addressing some common misconceptions about digital audio.  
 
Myth No. 1: Copies of files aren’t always perfect. Dubs between analog tape decks aren’t perfect; every time you make an analog copy, the signal degrades. It’s therefore natural to assume that all copying methods share that characteristic. Copying an audio file on a computer, however, is completely different from making an analog copy.

When you copy a file on a computer—whether it’s an audio file, a Microsoft Word document, or a shareware program—the operating system has to ensure that every byte of data copies correctly. If one byte in a Word document goes astray, you might get spelling errors, formatting problems, or worse. If one byte in a copy of a shareware program goes south, the software might not run at all.

Because of this situation, accurate copies of any file type are crucial, and digital-audio files are no exception. To prevent problems, the operating system uses a verification scheme to establish that all copies are byte-for-byte perfect. In the unlikely event that an error appears in the copy, the computer lets you know.

So when you copy an audio file from one hard drive to another or back up data to a tape drive or CD-R drive, rest assured that you’re creating a perfect duplicate.

FIG. 1: Apple’s new iTunes application lets you import audio files from compact discs, convert the files into MP3 format, and create playlists for listening (click image for larger view).
Myth No. 2: All file compression degrades audio. Compressed audio formats, such as MP3, have truly changed the face of recorded media by letting music be exchanged easily over the Internet. The MP3 format shrinks audio files using “lossy” compression, which means that not all of the musical data is actually stored in the MP3 file. The more important data is maintained while less important data is thrown away. The audio file is then reconstructed on playback with varying results in audio quality (see Fig. 1). In any event, MP3 audio quality is degraded somewhat with respect to the original file.

Because MP3 is one of the most widely known audio-compression formats, many people assume that all methods of compressing audio files work the same lossy way. However, not all of them do. Some programs, such as Emagic’s Zap and Waves’ TrackPac, are specifically designed for lossless audio compression (see Fig. 2). Those programs can’t shrink files as much as MP3 does, but they do retain all data while compressing files to about 50 percent of their original sizes.

Also lossless by design are general-purpose compression programs such as PKWare’s PKZIP, WinZip Computing’s WinZip, and Aladdin Systems’ StuffIt. To these programs, an audio file is just like a Microsoft Excel document; every byte of data must be retained. Again, the file-size reduction isn’t as dramatic as with MP3 compression (and it’s often less effective than audio-specific compression programs), but you can be sure that the quality of any zipped or stuffed audio file is completely unaffected by the compression.

FIG. 2: Emagic’s Zap is specifically designed to compress audio files without affecting the audio quality (click image for larger view).
Myth No. 3: CD quality. What the heck does “CD quality” mean, anyway? My cumulative annoyance at the misuse of this phrase leaves me feeling like a cranky old curmudgeon when I hear it. Sure, I’ll accept the description for any device that operates at 16 bits and 44.1 kHz—a CD player, for example—as long as its real-world performance measures up to the potential implied by those specs.

Unfortunately, the term is often used to describe almost anything that can spit out a tune. I’ve seen a $30 sound card with a 65 dB signal-to-noise ratio boast CD quality, even though 16 bits should offer a signal-to-noise ratio closer to 90 dB. Moreover, I’ve seen MP3 and MiniDisc players claiming CD quality, though those devices start with CD-quality audio and then shrink it using lossy compression, reducing both file size and fidelity. Soon we’ll have 4-bit digital toasters claiming their beeps are CD quality. Give me a break!



Reprinted with permission from Magazine, May, 2001
© 2000, Intertec Publishing, A Primedia Company All Rights Reserved


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