Whether you just like to listen to music, or you create and record it, you’ll be better off for knowing what “compression” means. If nothing else, you can impress your friends by knowing something geeky about audio. At best, you’ll be able to produce or listen to audio that is somehow louder and punchier without anyone having to turn up the volume. But as with any tool, it’s possible to overdo it with compression.
Okay, so what the heck is compression? Simply put, it’s a trash-compactor for sound. Why can that help audio sound better? For one thing, it evens out the loudness of, say, a song that has really quiet passages with occasional really loud passages. Have you ever been in a car, and a song started, and you could barely hear it? So you turn the volume up only to have your eardrums shredded when the loud parts of the song come in. You may have found yourself turning the volume up and down several times during a song to compensate for the extremes in quietness and loudness. What you were doing while turning it up and down was a form of compression! Yeah, you were compressing the audio by turning the loudest parts down and the quietest parts up.
Wouldn’t it be easier if you could just push a button on your car stereo and have that happen automatically? Well you probably can! The factory radio/CD player in my 2004 car has a button that simply has a “C” on it. I had no idea what it meant until I looked it up in the manual. Guess what the “C” stands for. Yup, “compression.” Check your manuals; there might be something similar on your CD Player.
By the way, I should mention that audio compression is not the same thing as “data compression.” For example, you may have seen something about mp3 or AAC audio formats being “compressed.” That’s talking about making the file size smaller so it can be more easily used on the web, and is NOT the same thing as what I’m talking about…just so you know.
So what about the folks recording or producing audio, or those who want to learn? How can you use compression? I have yet to meet the audio software, even the open source programs, that do not have built-in compressor tools. That’s how common and important it is in audio production. For example, when recording music, lead vocals pretty much always need some compression. Pop music tends to put a lot of compression on a lead vocal. That’s because it’s the most important thing in the song and in order to keep it loud enough to be heard through the music as it gets louder, but not overpower the music during the softer bits, a compressor is used to automatically even out the levels of the vocal track. One warning here though…if you overdo the compression on a vocal track, it tends to make the singer sound like they are lisping, and some other odd things.
Another useful way to use compression is to boost the average volume of an entire song (or whatever kind of audio you’re listening to). This is because the loudest an audio file can be without distorting (you know that nasty buzzing sound you hear when you turn the TV on too loud for your speakers?), the very loudest part of that audio file must not exceed a certain volume level. Many audio programs simply won’t allow you to turn audio up if the loudest bit of it will exceed that “distortion” ceiling. So if the audio is not loud enough, but you can’t increase the volume because there are just one or two places where it got really loud, and those are “bumping” up against that ceiling, you could just reduce the volume of ONLY those two places, leaving the rest of the audio alone. At that point, the loudest parts are much lower, and you can turn the whole thing up much louder before any of it bumps up against that ceiling again.
That last technique is often used when editing an entire song in order to make it seem much louder. Louder can often be interpreted as “better” by some people. But be careful here too. The more you compress a final mix, the less dynamic range the song has, which basically means it won’t get softer and louder as much. That can suck the life right out some audio.
So now you know what compression is. Cool, huh? If you want to experiment with recording and producing audio, there are lots of tutorials out there on the web. Of course I think you’ll like the ones at Home Brew Audio;). But I may be biased. Either way, go forth and either impress your friends, make the world safe for better audio, or both!