Speech recognition over different transmission channels will set demands to the parametric encoded/decoded speech. The effects of different types of noise have been studied a lot and the effects of the parameterization process in speech has been known to cause degradation in decoded speech when compared to the original speech. But does the encoding/decoding process modify the speech so much that it will cause degradation in the speech recognition result? If it does what may cause the speech recognition degradation? We have studied the effect of the parameterization and the causes of the nine different codec configurations to isolated word recognition.