Zoë Blade's notebook


MP3 tech specs

  • Released: 1991
  • Organisation: Fraunhofer Institute
  • Bitrates: 32 kbps, 40 kbps, 48 kbps, 56 kbps, 64 kbps, 80 kbps, 96 kbps, 112 kbps, 128 kbps, 160 kbps, 192 kbps, 224 kbps, 256 kbps, 320 kbps
  • Sample rates: 32 kHz, 44.1 kHz, 48 kHz
  • Tracks: mono, stereo

MPEG-1 Audio Layer III, or MP3 for short, was a phenomenally popular audio coding format.

It's compressed, in the sense that the filesize is compressed, not the dynamic range. Specifically, it's a form of lossy compression, meaning the encoded sound is missing some of the nuances of the original. This allows the files to take up far less space — for instance, encoding a CD quality wave file to a 128 kbps MP3 file subjectively sounds pretty close to the original quality, while taking up less than an eleventh of the space.

To oversimplify some of that lossy encoding, specifically masking, let's say you're listening to two intermittent sounds, a loud one and a quiet one. Whenever they both happen at once, the loud one obscures the quiet one. So the MP3 encoder would just remove the quiet sound whenever the loud one's happening at the same time, because you wouldn't be able to hear it anyway, so it makes no real practical difference.

With early MP3 encoders at lower bitrates, this didn't work very well. Hi-hats would sound notoriously sloshy. However, while the MP3 decoding standard for players was fixed, MP3 encoding for recorders was allowed to evolve. As long as a given encoder makes data that decoders can play back, it's up to that encoder's authors to decide which information can be discarded. By the time the MP3 format started to fade into obscurity (as people started streaming with a disregard to which codec was being used, just so long as it worked), encoders such as LAME (whose name isn't fooling anyone) sounded great, even at reasonably compact bitrates, such as the earlier-mentioned pirates' stalwart, 128 kbps.

Sure, lossy compression isn't perfect, but then neither was cassette tape. Both are pretty good tradeoffs for portable consumer use, when you want to take lots of music with you, to listen to in a noisy environment where you can't hear those nuances anyway. MiniDiscs used a similar lossy codec, Sony's own ATRAC.

Just as the Fraunhofer Institute shrank audio files, Toshiba then shrank hard drives, making them physically compact while retaining enough virtual space to store hundreds of albums in MP3 format. Monolithic portable music players such as the mid-2000s iPod Mini were a significant improvement from carrying around half a dozen MiniDiscs storing an album each. But that's another story.


Deep dives

Audio coding formats: MP3