What Is Bitrate?
Youve probably heard the term "bitrate" before, and you probably have a general idea of what it means, but just as a refresher, its probably a good idea to get acquainted with its official definition so you know how all this stuff works. Bitrate refers to the number of bits—or the amount of data—that are processed over a certain amount of time. In audio, this usually means kilobits per second. For example, the music you buy on iTunes is 256 kilobits per second, meaning there are 256 kilobits of data stored in every second of a song.
The higher the bitrate of a track, the more space it will take up on your computer. Generally, an audio CD will actually take up quite a bit of space, which is why its become common practice to compress those files down so you can fit more on your hard drive (or iPod, or Dropbox, or whatever). It is here where the argument over "lossless" and "lossy" audio comes in.
Lossless and Lossy Formats
When we say "lossless", we mean that we havent really altered the original file. That is, weve ripped a track from a CD to our hard drive, but havent compressed it to the point where weve lost any data. It is, for all intents and purposes, the same as the original CD track.
More often than not, however, you probably rip your music as "lossy". That is, youve taken a CD, ripped it to your hard drive, and compressed the tracks down so they dont take up as much space. A typical MP3 or AAC album probably takes up 100MB or so. That same album in lossless format, though—such as FLAC or ALAC (also known as Apple Lossless) would take up closer to 300MB, so its become common practice to use lossy formats for faster downloading and more hard drive savings.
The problem is that when you compress a file to save space, youre deleting chunks of data. Just like when you take a PNG screenshot of your computer screen, and compress it to a JPEG, your computer is taking the original data and "cheating" on certain parts of the image, making itmostly the same but with some loss of clarity and quality. Take the two images below as an example: the one on the right has clearly been compressed, and its quality has diminished as a result. (Youll probably want to expand the image for a closer look to see the differences—look at the foxs ears and nose).
Remember, of course, that youre still reaping the benefits of hard drive space with lossy music (which can make a big difference on a 32 GB iPhone), its just the tradeoff you make. There are different levels of lossiness, as well: 128kbps, for example, takes up very little space, but will also be lower quality than a larger 320kbps file, which is lower quality than an even larger 1,411 kbps file (which is considered lossless). However, theres a lot of argument as to whether most people can even hear the difference between different bitrates.
Does It Really Matter?
Since storage has become so cheap, listening to higher-bitrate audio is starting to become a more popular (and practical) practice. But is it worth the time, effort, and space? I always hate answering questions this way, but unfortunately the answer is: it depends.
Part of the equation is the gear you use. If youre using a quality pair of headphones or speakers, youre privy to a large range of sound. As such, youre more likely to notice certain imperfections that come with compressing music into lower bitrate files. You may notice that a certain level of detail is missing in low-quality MP3s; subtle background tracks might be more difficult to hear, the highs and lows wont be as dynamic, or you might just plain hear a bit of distortion. In these cases, you might want to get a higher bitrate track.