What format are audio CD files in? An explanation of the CDA and CD-DA format

The audio CD format is typically referred to as a CDA file (.cda). In truth there are no such things as CDA files as they are just created by the operating system to show representations of the audio tracks on a CD, however for convenience sake we will refer to CDA files in this help article.

CDA files can only be played from a CD and the files must be converted to WAV, MP3 or similar files for storage on a computer hard disc or DVD disc. The CDA format is an industry standard (referred to as the Red Book audio standard) that is used for encoding music on CDs and audio CDs bought in the high street will use this format.

When creating an audio CD the best source format to use is a WAV file (MP3s are always compressed from CD audio quality to some extent). Converting a 44.1 kHz WAV file to CDA introduces no noise, distortion or coloration to the sound.

CD audio uses a sample rate of 44.1 kHz and for stereo audio this requires 176,400 bytes per second (or 1,411,200 bits per second – there are 8 bits per byte) of data storage. This equates to about 10.09MB per minute of audio in CDA format.

So how do 700MB CD-R discs that you buy in the shops claim that you can store 80 minutes of CDA audio on them if over 10MB is required per minute of audio? The truth is that the capacity of a 700MB disc is actually much higher (over 804MB), but that the extra 14.915% of capacity is used by error correction code that is used to compensate for scratches and marks on the discs. This error correction space is essential on data discs where a single incorrect bit of data could corrupt the whole file. However on audio CDs this error correction space can be used as additional storage as any errors in the audio file will only appear as minor sound defects that probably wouldn’t be noticed by human ears and would not crash the CD player or computer that it was playing on.

So what is a CD-DA file?

CD-DA stands for Compact Disc-Digital Audio and was developed by Sony and Philips in the 1980s and is defined in the Red Book standard. It is exactly the same format as CDA, it is just that CDA is a more succinct abbreviation than CD-DA and so is more commonly used.

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