MP3 files are so common place that many are prone to forget what an unprecedented movement in the music and tech industry led to their invention. Whether you’re a convenience loving MP3 appreciator or an audiophile worried about the quality loss that MP3’s represent, you may be interested to hear exactly how they work and how they first came about.
First of all, MP3’s came into existence when CD’s were already a thing. A CD stores a song as digital information, and its data is imprinted in an uncompressed, high-resolution format. In creating a CD, music is sampled 44,100 times per second. Each of these samples are composed of 2 bytes, which are each 16 bits long. Separate samples are taken for the left and right speakers in a stereo system, so a CD stores a huge amount of bits for every second of music that is played off of it. The average song on a CD take up about 32 million bytes of space.
The MP3 format is a compression system for music. It constitutes as attempt to compress a CD-quality song by a factor of 10 to 14 without affecting the sound noticeably. That means that a CD’s 32MB song can be compressed down to 3 MB of space, the average amount of space taken up by an MP3. The compression of these audio files allows for faster downloads and the storage of more songs on your computer’s memory.
Compressing files is extremely common for images and text, but can it be done for songs without losing an important amount of quality? That’s up for debate, and there are many audiophiles that vehemently oppose file compression. The algorithms used for compressing sound files use a technique called perceptual noise shaping to make the transition as graceful as possible.
Perceptual noise shaping takes into consideration factors of the human ear and how people perceive noise during the process of audio file compression. It considers the fact that there are certain sounds that the human ear cannot hear, there are sounds the human ear hears much better than others, and if there are two sounds playing simultaneously, we hear the louder one but have difficulty hearing the softer one.
With these facts taken into consideration, aspects of the song can be eliminated without drastically changing human perception of the song. Using these techniques, files can be compressed while retaining “near-CD-quality” sound.
Compression techniques differ, as do the qualities of different MP3 files. For example, you can actually create an MP3 file that isn’t compressed at all, it will just be much larger than a standard compressed file. It won’t be in the “lossy format” that allows MP3s to be so small and convenient, but it will also not have undergone any loss of sound.
You can decide how much information an MP3 file will retain or lose during the encoding and compression process. It’s actually possible to create two different MP3 files with differing sound quality and file sizes from the exact same source of data. The determining factor here is the bit rate; the number of bits per second encoded into the MP3 file. Most MP3 software allows for the user to select the bit rate during the conversion process. The lower the bit rate, the more information ends up discarded in compression. A bitrate of 128 Kbps results in what you generally hear on the radio. A bit rate of 160 Kbps or higher is recommended for people who want MP3 files with sound quality as excellent as that of a CD.