darrenyeats;675031 Wrote: > You are right, the examples tend to use a steady tone. > > You say that dithering doesn't work for constantly changing signals. > Why do you say that? > > Regards, > Darren
Because dithering works by averaging. For instance if you had a steady value that should be reading 9.5 but the resolution of the your ADC could only read whole numbers, you could never get any closer than 0.5 of the correct reading. You can only read 9 or 10. But if you add noise to the desired signal, and the noise is random and at least high enough to move the reading +/1 digit, then if you took a large number of readings of the signal that is at 9.5 it would read 9 sometimes and 10 other times due to the noise, but if you averaged out a large number of readings, then the averaged reading would be 9.5, effectively increasing the resolution of the system. But if you can't make a large number of readings on the same value with the noise added, it doesn't work. In fact, if you can only make one reading before the value changes due to actual changes of the input value, then the noise just makes the reading less accurate. Obviously, music isn't changing instantaneously, but it will rarely be steady state enough to allow many samples of the same waveform on a row. In the case used as an example on the web page mention, the 1kHz tone would have to be present for 743 milliSeconds. That is 7 full cycles of the 1kHz waveform. Can we expect that a music waveform would be that steady? I'm sure that dithering does help to some extent on music, but the extent would depend on the statistics of music. Just how dynamic is it? I've never seen any good discussion on it. Another way to look at it is hinted at in the web page we are talking about. He talks about how making a large number of samples effectively reduces the noise by binning the frequency into smaller bands, each containing less noise. But that can't apply when the signal is moving over the full bandwidth while the averaging is happening. You would just average the signal along with the noise. Terry -- TerryS ------------------------------------------------------------------------ TerryS's Profile: http://forums.slimdevices.com/member.php?userid=40835 View this thread: http://forums.slimdevices.com/showthread.php?t=89733 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/audiophiles
