stadlin@hou2h.UUCP (Art Stadlin) (01/16/85)
Bring out the textbook... +++++++++++++++++++++ The SAMPLING THEOREM states that, if a function of time f(t) contains no frequencies higher than W hertz, f(t) is *completely* determined by giving the value of the function at a series of points spaced 1/2W seconds apart. "It is important to note that the theorem makes no mention of the time origin of the samples. The time origin is unimportant; it is only the *spacing* of the samples which matters." +++++++++++++++++++++ MY CONCLUSION: The analog source signal (orchestra, etc.) contains frequencies above human hearing. Therefore, if it is desired to sample this signal at a 40~kHz rate, the analog signal must first be low-pass filtered to assure no frequency components greater than 20~kHz. Since a "perfect" 20~kHz low-pass filter is very expensive, the recording industry probably uses a "less-than-perfect" low-pass filter at, say, 35~kHz. Then the signal is sampled at an 80~kHz rate, just to be sure. -- \\\ \\\\ Art Stadlin \\\\\\________!{akgua,ihnp4,houxm}!hou2h!stadlin