Contrary to popular belief, digital systems are not perfect. This is especially true when like and unlike digital systems are concatenated with other digital and analog transmission systems. These systems add thermal noise, quantization noise and, in the case of compressed systems, compression artifacts. Several questions and misbeliefs exist as to how these degradations combine on a subjective and objective basis. This paper presents both objective and subjective results of • cascading quantization noise from linear PCM systems; • the effects of combining quantization noise and thermal noise, and • the effects of combining, thermal noise and compression artifacts. The industry is proficient at thermal noise measurements today. Quantization noise measurements are also becoming more consistent through the use of shallow ramp measurements. Compressed signals, however, still offer several challenges. Certain test scenes may look fine on a particular codec, while other scenes may cause significant artifacts.The analysis of the test results collected during the evaluation indicate that quantization noise adds similarly to thermal noise both objectively and subjectively. It also indicates that certain compression artifacts contribute subjectively as noise additions. This paper presents these results and analyzes the relationship for cascaded thermal noise, quantization errors, and compression artifacts.