Lossy Compressed Formats

When you rip or copy a digital audio file, you can either copy the file exactly (in non-compressed format) or you can use some sort of compression to reduce the otherwise-huge file sizes. If you choose a compressed format, you can opt for formats that use either lossy or lossless compression. Lossy compression loses some of the original audio information to create a smaller file, resulting in music that isn't quite as good-sounding as the original. Lossless compression doesn't affect the original sound quality, but results in larger files sizes-although not nearly as big as non-compressed files.

Lossy compression works by sampling the original file and removing those ranges of sounds that the average listener can't hear. A lossless encoder uses complex algorithms to determine what sounds a human is able to hear, based on accepted psychoacoustic models, and chops off those sounds outside this range. You can control the sound quality and the size of the resulting file by selecting different sampling rates for the data. The less sampling going on, the smaller the file size-and the lower the sound quality.

The problem with shrinking files to this degree, of course, is that by making a smaller file, you've dramatically reduced the sampling rate of the music. This results in music that sounds compressed; it won't have the high-frequency response or the dynamic range (the difference between soft and loud passages) of the original recording. To many users, the sound of the compressed file will be acceptable, much like listening to an FM radio station. To other users, however, the compression presents an unacceptable alternative to high-fidelity reproduction.

The most popular lossy compressed format today is the MP3 format, although there are many other formats that work in the same fashion. Here's a list of available lossy formats:

• Advanced Audio Coding (AAC, M4A). Also known as MPEG-4 AAC, this is the audio format used by Apple's iTunes and iPod. AAC offers slightly better sound quality than MP3 files; AAC files can also be subject to digital rights management protection. While older versions of Windows Media Player couldn't play the AAC format, Windows Media Player 12 (included with Windows 7) is fully compatible with both AAC and M4A format files-as long as the files don't have DRM encoding.
• MP3 (MP3). Short for MPEG-1 Level 3, the MP3 format is the most widely used digital audio format today, with a decent compromise between small file size and sound quality. The primary advantage of MP3 is its universality; unlike most other file formats, just about every digital music player and player program (including Windows Media Player) can handle MP3-format music.
• OGG Vorbis (OGG). An open-source encoding technology originally known as "Squish," OGG Vorbis was designed as a substitute for MP3 and WMA. It uses variable bit rate compression, which encodes different parts of a song with higher or lower compression, to produce better quality when needed.
• RealAudio Media (RA, RM, RMA). Proprietary format used by Real Networks, designed particularly for real-time streaming audio feeds.
• Windows Media Audio (WMA). Microsoft's digital audio format is promoted as an MP3 alternative with similar audio quality at half the file size. That may be stretching it a bit, but WMA does typically offer a slightly better compromise between compression and quality than you find with MP3 files. The iPod, however, cannot play WMA format files-nor can the iTunes music player.