The Illusion Of Volume: Understanding Compression

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Art and life co-habitate, informing, imitating, and enriching each other constantly. Each week in Better Living Through Music, RFT Music writer Ryan Wasoba explores this symbiotic relationship.

The CALM Act was enacted two months ago, causing television commercials to maintain the same or lower volumes than television programs. The change is noticeable; transitions between Tosh.O and ads starring toilet-paper connoisseur bears have been greatly smoothed. Most folks are unaware that digital music is subject to a similar limitation, and any sound that exceeds a certain volume distorts and generally sounds awful. This law is governed by science and technology instead of the FCC, and it has caused "compression" to become a buzzword and a vital component to understanding the sound of modern music.

There are two ways that music is compressed, and each one greatly impacts its sound. When an mp3 is made, actual chunks of the song's data are removed in order to shrink the size of the file; otherwise, a three minute song would be roughly 30 megabytes and iPods would barely be able to contain all your Smiths B-sides. The quality of an mp3 file is determined by how much information remains after this type of compression.

The less obvious form of compression happens during the processes of making a recording. This compression is applied by the music makers or the music manipulators. It brings the quiet and loud parts of a sound closer together in volume, and the applications are numerous. During a recording, compression can level out an expressive singer who yells some words and mumbles others. While mixing, compression makes the subtle elements of a snare drum's sound easier to hear. Sometimes raising valleys and lowering peaks helps instruments stack into a song, the same way flat paper piles up more evenly than folded paper. Over the past decade artful compression has been responsible for fascinating records. Without compressors, Broken Social Scene's You Forgot It In People would not exist.

However, too much flattening makes a recording sound, well, flat. A track too compressed can sound like noise, and we experience this every time we land on a radio station mid-song and wonder "What song is this?" Turns out it's "Smells Like Teen Spirit," overcompressed to appear louder than what is playing elsewhere on the dial.

The human ear usually perceives louder as better, and compression has become a way to exploit this principle. Since a song cannot exceed a certain volume without distorting (and not the good kind of distortion), the ear is tricked by the illusion of volume. In this application, compression pushes every element of a sound closer to the maximum level. This is one element of the mysterious process of "mastering," which great engineers do without negatively impacting the sound. Pushing too hard causes frequencies to pile up, much like the way people cram together to get closer to the stage at a concert. The ear is the poor sap at the front being folded in half over the front barricade.

Even with all the tricks at hand, the maximum volume achievable by digital audio is constantly surpassed and amateur, distorted recordings are everywhere. Metallica's St. Anger is notorious for crossing the threshold; some non-audiophile customers even returned the disc claiming it defective. Anybody who makes music has the facility to make it too loud, and it's as much a moral decision as a technical one. Truly, making a digitally distorted record is breaking a law.

It is unlikely that any music equivalent to the CALM Act will take place. From a technical standpoint, digital audio is self-limiting. From a practical standpoint, the music industry has no legs the way the television or movie industries do. Those people can unionize, but it's the Wild Wild West out here.

For musicians, understanding compression is part of comprehending the way your music is presented. For listeners, understanding compression is knowing how those behind the audio signal perceive you as a consumer. Don't let an artist throw the loudest, harshest sounds at you like pickup lines in a sleazy attempt to weasel into your ears. We need peaks, we need valleys, we need drama. We need to be wooed.

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