A "Red Book" CD--the kind you have at home to play music off of, holds around 700~800 mb of digital information; which is around 72 minutes of stereo music. In creating this CD, the original music from the master recording was sampled at a rate of 44,000 Hz (cycles per second for us old folks); in other words, to audio frequencies up to 22,000 Hz. Typically, human hearing drops off fast past 15,000 Hz., a piano tops out at around 5,500 Hz., some chimes at around 8,000 hz. However there are overtones and harmonics that reach this high, and create the "natural" sound of the instruments.
The digital encoding method used to create a CD uses a small amount of data compression. That is, a certain amount of repetitive information is "thrown away," in order to extend the amount of information that can be put on the CD. But this compression is very minimal
A .WAV file is a type of digital file used in most audio editors. The "wake-up" sound that windows plays when it boots up is a .wav file. WAV files can be encoded at different sample rates and different bit rates, depending upon their purpose. They are considered linear because there is no data compression used when the audio is converted to a digital file; one determines how big or small the file will be for a given length of audio by changing the sample rate, and bit rate--with a trade-off in playback quality--lower frequency response as the sample rate goes lower. Most WAV files are 16 bit, though 8 bit can be used for low quality audio. Fewer bits==less information converted from the original audio.
If you were to record a CD cut real time as a 44 KHZ. 16 bit file, you would have audio quality almost identical to the original CD. This file would take about 10 mb per minute of stereo audio. MPEG-3 is a standardized data compression scheme. The theoretical frequency response of the music piece is somewhat preserved, but "duplicate" information is thrown away in order to shrink the size of the resulting file. A lot of information. That same 1 minute stereo recording in MPEG-3 would be less than a megabyte per minute in hard disk space. But there is no such thing as a free lunch. Hence, if you recorded that same CD cut real time as an MPEG-3 file, and compared it with the 44 khz. WAV file, there would be an apparent difference in quality. Not necessarily in frequency response, but in the sense that certain sounds/instruments would not sound quite right.
Not a problem if you are listening on ear buds off an IPOD, or through tiny little plastic computer speakers. However, on an FM station, programing from MPEG-3 will never sound as good as the programming of the same music on another station using WAV files.
Many automation systems will handle both MPEG-3 and WAV files, although they may not be able to overlap them on playback. As mentioned, hard drives are cheap, a 500 gb drive could easily handle the typical 500~700 song library used in many radio formats. So a prudent thing to do, especially if you have the original CD's (or can borrow them again) is to re-do your library as 44 KHZ 16 bit .WAV files.
