You’ve probably heard that you clean CDs from the centre outwards, and not in an arc.

Here’s why.

Audio CDs have error correction. Technically it’s called Cross-Interleaved Reed-Solomon Code, or CIRC for short.

There are two levels of error correction, C1 and C2. C1 corrects bit errors, and C2 corrects frame errors. An audio CD frame hold 192 bits (24 bytes), and there are 98 frames per sector.

The audio data and the error correction data are interleaved, which means they are mixed up in the data stream read by your CD player. The theory is that a surface defect will affect data in a sequence; when your player does its de-interleaving thing on playback, the affected data is out of sequence and there’s a much better chance it can be recreated.

On playback, the CD player is smart enough to de-interleave the data, separate out the audio data and error correction data and, if it finds errors, will use the error correction data to recreate the original audio. If not, it will interpolate between known good samples to get a reasonable value to insert into the audio stream.

If you clean your CD in a circular motion you run the risk of making both the audio and error correction information unreadable because you may damage too much data in a single track. This will give you clicks, pops, or may even make the player skip a second or two of audio.

If you clean from the centre out, any scratches you make will cut across multiple tracks. The error correction can do its thing, and you’ll get perfect playback even with those scratches.

Note that some computer CD drives are able to report back the number of uncorrected C2 errors. They may be so small that you can’t hear them, yet your ripping software can use this information to figure out whether you’ve achieved a perfect rip or not.