For many years, this specific file size/bitrate combination was considered the standard for portable music. It made it possible to fit hundreds of songs on 512MB USB drives or early iPods.

By compressing the data to a constant bitrate of 128 kbps, the 5-minute song is shrunken down to just 3.41 MB .

The encoder acts as an audio engineer, analyzing the music. It uses psychoacoustics to remove sounds the human ear is less likely to hear, such as extremely high frequencies masked by louder, lower sounds.

To make it portable, the song passes through an MP3 encoder at (kilobits per second).

Imagine a vibrant, live studio recording—a 5-minute song featuring drums, bass, vocals, and a shimmering acoustic guitar. In its original form, this uncompressed audio (like a WAV or AIFF file) is huge, perhaps 50 MB, taking up valuable space on an old-school MP3 player.