We have all heard the familiar clicks and skips from our CD Audio Player that result from a scratched, damaged, or dirty CD disc. Sometimes the effects of disc defects can be subtle and result in audio distortion instead of obvious click and skips. This distortion results from the inability of standard CD player's error correction codes (ECC) to correct for the ablation of the underlying audio information by a scratch defect or electrical noise.

In fact, when the CD ECC fails, many CD drives have special circuitry called "error concealment" circuitry to conceal the errors that ECC was unable to fix. The error concealment circuitry introduces distortion while it tries to interpolate through the errors. Many types if error concealment circuity will even insert audio noise when activated to mask the errors. This is hardly what lovers of high fidelity audio reproduction seek.

In order to complete this article we used information from:

1. Calimetrics (http://www.calimetrics.com)
2. ECMA (http://www.ecma.ch/)
3. Kelin Kuhn's paper (http://www.ee.washington.edu/conselec/CE/kuhn/cdaudio/95x6.htm)
4. Clover Systems (http://www.cloversystems.com)
5. YAMAHA Japan (http://www.yamaha.co.jp/computer)
6. Plextor Europe (http://www.plextor.be)
7. Pioneer Japan (http://www.pioneer.co.jp)
8. Quantized (http://www.quantized.com)
9. MS Science (http://www.mscience.com)
10. Philips (http://www.licensing.philips.com)
11. Advanced Surface Microscopy (http://www.asmicro.com/)
12. Eclipse Data (http://www.eclipsedata.com)
13. MMC Draft Standard (http://www.t10.org)
14. JVC Japan (http://www.victor.co.jp/products/others/ENCK2.html)