Windows 7 / Getting Started

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Choosing Music File Formats

When you're working with your digital music in Windows, it helps to know a little bit about the various music file formats available. That's because when you're ripping tracks from a CD, you have a choice as to what file format and bit rate to use-and these choices affect not only the size of the resulting file, but the audio quality as well.

How Digital Sampling Works

To better understand digital music formats, let's start at the beginning of the process-in the recording studio. All digital recordings are made by creating digital samples of the original sound. The way it works is that special software "listens" to the music and takes a digital snapshot of the music at a particular point in time. The length of that snapshot (measured in bits) and the number of snapshots per second (called the sampling rate) determine the quality of the reproduction. The more samples per second, the more accurate the resulting "picture" of the original music.

For example, compact discs sample music at a 44.1kHz rate-in other words, the music is sampled, digitally, 44,100 times per second. Each sample is 16 bits long. When you multiply the sampling rate by the sample size and the number of channels (two for stereo), you end up with a bit rate. For CDs, you multiply 44,100 x 16 x 2, and end up with 1,400,000 bits per second-or 1,400Kbps.

All these bits are converted into data that is then copied onto some sort of storage medium. In the case of CDs, the storage medium is the compact disc itself; you can also store this digital audio data on hard disk drives, or in computer memory.

The space taken up by these bits can add up quickly. If you take a typical three-minute song recorded at 44.1KHz, you end up using 32MB of disk space. While that song can easily fit on a 700MB CD, it's much too large to download over a standard Internet connection, or to store on a portable music player.

This is where audio compression comes in. By taking selected bits out of the original audio file, the file size is compressed. If the right bits are excised, you'll never miss them.