Some years ago, when digital music starting replacing CDs and LPs, people took sides and arguments ensued. But here’s what’s funny: The digital crowd broke up into cults that favored different file formats like MP3, AAC, and WMA. From the outside, it’s hard to know what the fuss is about or if average music listeners really need to know about any of this. Music was supposed be relaxing and now it involves math. Ugh.
What is audio compression?
These different file formats are often about something called compression — that thing that makes audio files smaller. A smaller files takes up less space on your device and, if you’re streaming, eats up less of your data plan. But how does it work? And what happens to the sound when you compress an audio file?
In a previous post, Bytes, Bits and What Bits-Per-Pixel Actually Means, we discussed the concepts of bits. Quick review: Bits are the building blocks of digital files. More bits means a bigger, and probably more sophisticated, file. With audio files we use the term “bit-rate” which tells you how many “bits” are being used per second as the music plays. Think of it sort of like the thread count in sheets. A higher thread count results in a smoother, silkier sheet, just as a higher bit-rate results in a better sounding audio file.
An audio file with no compression is called a full resolution file. Music with a WAV file extension, for example (which is what you’ll find on music CDs) has no compression. But most of us have ditched our CDs and listen on our computer, phones, or stream over the Internet. That means that full resolution files like WAV take up too much space and are too slow when streaming or downloading. We need a way to shrink those files down — enter audio compression.
The most recognizable type of compressed audio file is the MP3, but others types include AAC and WMA. While they differ, the basic concept is the same, and it’s surprisingly simple.
You know that saying, “What you don’t know, you can’t miss”? Okay, maybe I made it up, but just go with it. Basically, audio compression makes the file smaller by leaving out some of the information that you didn’t even know was there.
For example, pretend you’re camping in the Mojave desert. You look up at the sky and marvel at the countless stars in the sky. In reality, you’re only seeing a tiny fraction of the stars in the galaxy because of the limitations of the human eye. But, even though you didn’t see all of the stars, you saw enough of them to get that heavenly feeling.
Audio compression works the same way. Just like your eyes only see part of the night sky, studies show that your ears only hear part of the actual sound. I touched on this in my post on volume and loudness. Your brain prioritizes certain sounds, and lets other go by virtually unnoticed. You might be surprised to hear (sorry, I couldn’t resist) that up to 75 percent of the information from a sound file can be removed before most of us notice any difference! Astonishing.
Of course, you have to draw the line somewhere. Compress (remove) too much and you get a super small file that sounds trashy. Compress too little and you don’t benefit from the file size reduction. Some audio snobs will say they can hear the difference, but it’s hard to tell the difference between a full resolution WAV file and an MP3 compressed to 25 percent. Don’t believe me? Test for yourself using the nifty free app ABX . Drop me a line and let me know how you did.
I tried it and was surprised to learn that I couldn’t tell! Since I am an audio guy, at first I was bummed. But then I remembered that my memory isn’t that great anymore. Soon I’ll forget that my ears are just average. And you know what they say: “What you don’t know, you can’t miss.” Wait, did I already say that?
Image credits: Jonathan Grossman