To encode files, you can use a jukebox program (such as iTunes), a sound editing program (such as Sony’s Sound Forge), a specialized recording program (such as Windows Media Player), or a dedicated encoding program (such as Discreet’s cleaner XL software). If you are curious as to what happens during the encoding process, refer to Chapters 8 and 10.
The essential point is that encoding is a game of tradeoffs between file size and sound quality. When you encode files in a compressed “lossy” format like MP3, certain bits of sound data are discarded to make the file smaller. Although the data that’s discarded is normally inaudible or redundant, the more you discard (i.e., by lowering the bit-rate), the worse your audio file will sound. The following section will help you understand the settings that control the size and quality of the MP3 files you create.
As mentioned in earlier chapters, the term bit-rate refers to how many bits (1s and 0s) are used to represent each second of an analog audio signal when it is converted to digital. MP3 files can be encoded at bit-rates from 8 kbps to 320 kbps. Lower bit-rates result in smaller files with poorer sound quality, while higher bit-rates result in better sound quality, but larger files. Below is a formula for calculating the size of a digital audio file encoded at a constant bit-rate. In the example, a 3-minute (180-second) song encoded at 128 kbps results in a 2,812.5-KB (2.75-MB) file.
bit-rate x time in seconds / 8 (bits/byte) ...