Bit Rate

The bit rate of a digital file is defined as how many bits it uses up in a given interval of time. (An audio file is almost always measured in "kilobits per second".) Typically, the higher the bit rate at which music is encoded, the better the sound is. A rate of 128 kilobits/sec is extremely popular in online music downloading - legal and otherwise - because it offers a good compromise between sound quality and download time. Here's a little chart to give you an idea of how different bit rates compare to regular CD audio.

Bit rate (kbits/sec)Seen inCompression Ratio (Compared to CD Audio)Three-Minute Songs per 650 megabyte CD
1411CD Audio 1:1 20
192High quality MP3, WMA, or AAC 7.3:1 154
128Most downloaded music (legal or otherwise) 11:1 231
64High-quality streaming music; small memory-based portable devices 22:1 462
8Streaming voice; Internet talk radio 176:13,697

Bit rates lower than 128 kbits/sec are generally not suitable for CD or hard drive-based devices, but rates between 64 and 128 are great for devices with only 64 or 128 MB of memory where you want to pack on more songs, or even for streaming Internet radio if the listeners have broadband connections. Very low bit rates (below 64 kbps) are almost totally unsuitable for music but compress voice fairly well and can be used for online voice chat or streaming talk/news radio. Of course, there's always the option of using a variable bit rate.


These common acronyms stand for Variable Bit Rate and Constant Bit Rate, respectively. Constant Bit Rate audio files are the most common - they use up the exact same amount of data from one moment to the next. If you have a 128 kb/s CBR music file, it will use 128 kilobits to describe the audio in each second of the song, regardless of what sounds are playing that second or the complexity of the audio stream at the time. A Variable Bit Rate is a bit smarter. A VBR music file will use a lower bit rate in areas of the song that are simpler to compress accurately, and then higher bit rates in parts that require more bits to describe accurately. VBR audio files are often made with a certain quality in mind, rather than a certain bit rate, but it's almost always true that, all things being equal, a VBR sound file will sound better than a CBR file of the same size. The problem with VBR is that it's hard to stream over the Internet, because the amount of data that needs to come over your net connection is constantly changing from one moment to the next.

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