MP3 Audio Files and Bitrates



The bitrate of an audio file is a key indicator of the quality level of that file. It can spell the difference between a song you love to hear and one that grates on your nerves.

In essence, every second of music that plays out of your computer is represented by a bunch of bits on your computer's hard drive. If only a few bits represent that second, the music is going to sound very choppy and low quality - sort of like it was playing from an old AM radio. However, if that same second is represented by a ton of bits, now the sound is very high quality, as if you were sitting in the second row of a concert hall and hearing the music coming directly at your ears.

Keep in mind that the bit rate per second would stay constant through the compression process, regardless of what the music was doing. So if the program was working on the intro where it was just a simple keyboard progression, the program might do very well with this, giving a very high quality output because all it had to reproduce was four piano notes. However, later in the song, when the drum solo began with trillions of hits per second, the exact same MP3 file would now have low quality output, because it was trying to jam all of that drum sound information into the same amount of bit space.

Some newer software packages use Variable Bit Rate (or VBR) which means that the software will use fewer bits when the extra aren't necessary, and then more bits for the complicated musical passages where there is a lot going on. VBR would therefore always give a much better quality output when compared to the old styles of recording (average bit rate or constant bit rate).

Let's say you settle on a given bit rate for a given format (say MP3s) because you feel it gives a good sound for the file size. You cannot compare that bitrate directly to the exact same bitrate in other formats, say WMA files. That means that a MP3 file that is "2000 bits" cannot be compared directly to a WMA file that is "2000 bits" and have it be said that "Oh they're both the same # of bits, they must be the same quality of sound". If the compression technique that does WMA compression does a better job than the compression technique that does MP3 compression, then the WMA file may be just as high quality sounding even with the exact same number of actual bits sitting on your hard drive.

That is, let's say a MP3 file uses a low quality way for 'squashing' the original file onto your hard drive. It doesn't squash very well and leaves lots of blank spaces. Next, let's say a WMA file does a much better job of 'squashing', making sure there are no blank spaces left in the file. When you look at the end result, the MP3 file might take up 20mb and the WMA file could only take up 10mb. The MP3 file would have a higher "bits per second" count, but the actual audio quality on both files would be the same.

The audio quality can even vary from software package to software package for the exact same format. Let's say you were making MP3 files, but you had 8 different software packages you were testing out. Let's say you then made 8 different MP3 versions of Vivaldi's Four Seasons CD, from the same source CD. Even though all of the resulting files were MP3 files, some would sound better than others - all depending on the quality of your software package that did the compression.

Typical Bitrates:
CD - 128 kbps
FM Radio - 64 kbps
AM Radio - 32 kbps
short-wave Radio - 16 kbps
telephone - 8 kbps

Music Format Types
Music / MP3 Tips and Information