http://www.trevormarshall.com/byte_articles/byte6.htm From Jan 8, 2001 Comments on the article, Spring 2014 Trevor writes about music quality in recordings, using higher sampling rates. He shows photos of oscilloscope tubes with input from various CD players, using a recording of a square wave, with 20 kHz filtering (the edge of human hearing). While the point Trevor makes is that increased sampling improves 20 kHz filter quality (just going from samples of 44,100 to 48,000 doubles the quality), perhaps the curious photos are of more interest, in view of your current study of Fourier series. I hope you can understand what causes the errors in the wave forms. Marshall has an explanation, which you can applaud or criticize. All Sound Can Be Decomposed Into Sine Waves First, the 1-KHz square wave is actually made up of an (essentially) infinite number of sinusoids at 1 KHz, 3 Khz, 5 KHz, and so on. When some of these sinusoids are removed from the square wave, the transition between the levels becomes less steep, and the "ringing" appears. This effect occurs whenever you filter the square wave to remove its higher-frequency components.