MP3s are artificially downsized files, i.e. they are compressed.
When a MP3 file is created, in simple terms, frequencies are omitted that the human ear cannot perceive or can barely perceive.
Thus, most lossy MP3 compression algorithms take advantage of psychoacoustic effects of human perception of sound events: our hearing cannot perceive certain sounds or can hardly perceive them, e.g. quiet sounds immediately following very loud ones.
These MP3 compression tools then try to encode the source material in such a way that the finished MP3 file ideally sounds like the original.
Thus, with different data rates, the file size is significantly reduced.
MP3 files should have a data rate of at least 128 kbit/s (kilobits per second), so that the quality is just right. The larger the data rate, the “better” the MP3 file sounds, but also the larger the file size.
In this day and age of streaming, fewer and fewer are fiddling with MP3 files. Fortunately, because there are better alternatives! If you want to digitize your CD collection, you should avoid MP3 and go for the lossless FLAC (“Free Lossless Audio Codec”) format. The file sizes are larger, but nowadays storage space is no longer an issue.
