SuperQ;626734 Wrote: > It sounds like they're using something like audio diffmaker. It should > be easy to reproduce their results.
Exactly. They reach the conclusion that the error signal is proportional to the time rate of change of the signal being tested. Why do you suppose this is? Let's look at the definition of the derivative of a time function f(t) (that is, its instantaneous time rate of change). df(t)/dt = limit as delta_t approaches zero of (f(t+delta_t)-f(t)) / delta_t The idea of their measurement is to introduce the appropriate delay into one of two signals that are nominally almost equal, except for a delay, such that when you subtract them, you get almost zero. But suppose there's a small error in the computed delay. Then you get a time function that looks like this: g(t) = f(t+delta_t)-f(t) which is indeed directly proportional to the derivative of f(t), with a constant of proportionality delta_t. Notice in their presentation, they do not label the vertical axis of the graphs of this difference signal, making the results highly suspect. But as anyone with experience with DiffMaker will attest, if one creates two signals that differ by only a delay (best done digitally), DiffMaker does such a good job of finding the optimum delay before subtraction that the difference signal is too small to be above the noise. This is true even for delays that are not an integer multiple of the sample period. It automatically takes care of that too. So it appears the error signal they're seeing is just from inaccurate computation of the delay between the two signals. They're trying to reinvent the freeware DiffMaker and doing a much poorer job. Whether this is deliberate or not I'll leave up to you. -- andy_c ------------------------------------------------------------------------ andy_c's Profile: http://forums.slimdevices.com/member.php?userid=3128 View this thread: http://forums.slimdevices.com/showthread.php?t=87175 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/audiophiles
