CDA files copied from a CD to a computer hard drive do not contain any audio information. These copied CDA files are essentially track markers; they function as a table of contents. The acoustic information encoded on CDs is produced by a digital sampling technique that converts analog data into binary data. The technique is called Pulse Code Modulation (PCM). PCM files are uncompressed audio data files. It's the PCM files that contain the actual streams of audio data, while the CDA files mark the beginning and end of each PCM file.
Each CDA file on your CD points to the location of a specific PCM audio stream file on your CD. The CDA file provides the link that allows you to quickly jump to the beginning of each audio track on your CD.
CDA files are formatted for storage on compact disc media. You cannot store CDA files on an MP3 player, iPod, or any other digital audio playback device incapable of playing compact discs. CDA files are only compatible with CD playback devices such as your CD player, DVD player, or the CD-ROM on your computer.
You can only play CDA files from a CD. When you save the CDA files found on your CD to your computer, for instance, you do not save the actual audio track. You merely save the file ID for the audio track. That's why when you look at the file properties of a CDA file on your computer, the file size is so small. The CDA files generated by the Windows operating system have a file size of only 44 bytes. The application shortcuts on your desktop take up more space than this.
In order to save the audio data stored on a CD to your computer, MP3 player, or some other digital playback device, the CDA files on your CD have to be converted to another format. To save the audio data stored on a CD to your computer, for example, you have to use ripping software (such as Windows Media Player), which can access the actual audio data stored on the CD and convert it to a WAV, AIFF, or RAWS file. There are many CDA conversion software applications available on the web for free and for puchchase. Make sure the application you download supports the file format you would like to convert your CDA file to, such as MP3, WAV, or M4A.