MP3s have become so ubiquitous that we often forget it's a compression format. When music gets trimmed to one-tenth of its original size, lots of information deemed "unimportant" gets tossed out. Here's what we're missing.
The video up top is called "moDernist." Ryan Maguire, a Ph.D. student in Composition and Computer Technologies at the University of Virginia Center for Computer Music, explains how he created it on his website, The Ghost in the MP3:
"moDernisT" was created by salvaging the sounds lost to mp3 compression from the song "Tom's Diner", famously used as one of the main controls in the listening tests to develop the MP3 encoding algorithm. Here we find the form of the song intact, but the details are just remnants of the original. Similarly, the video contains only material which was left behind during mp4 video compression.
Maguire says he used a 320 kbps bitrate because lower bit rates simply sounded more like the original, which would make sense given that more information about the music is being left out. Typically, a 4-minute song in uncompressed digital audio (usually a .WAV at 2-channels of LPCM audio at 16-bit sampled at 44,100 Hz) is about 40 MB. That translates to a rate of 1,411.2 kbps. After MP3 compression, a file can be squeezed down to about a tenth of the original, or a 4 MB size audio file; most mp3s are between 128 and 320 kpbs.
MP3s result in what's called "lossy compression"; data is lost and the quality is never as good as the original full bandwidth audio. MP3s reduce the accuracy of certain sounds considered to be beyond our auditory perception (which is why the method is often referred to as "perceptual coding"). For example, the human range for hearing is between 20 to 20,000 Hz, which is why CD quality audio is sampled as high as it is.
But as Maguire's project clearly demonstrates, there's lots of perceptual material that's getting tossed out.
For audiophiles, this has always posed a problem, who argue that MP3s (and other compression schemes) introduce artifacts (such as mp3 "sizzle", added distortion, flat two-dimension sound, and mushiness), while diminishing the full acoustic spectrum. At the same time, because bandwidth rates and hard drive space have dramatically improved since the introduction of MP3s, there's less of a need to rely on compression schemes.
[ Via Death and Taxes ]