Pat Farrell;182640 Wrote: > Muggy wrote: > > I think that both those method would change the frequency content of > > the signal. > > Not nearly as much as your example. > > > By adding zeros between samples, the frequency content is > > mirrored/repeated at higher frequencies and this can then be removed > by > > filtering leaving an upsampled signal with the same frequency content > as > > the original. > > > > Taking your example:- > > 0, 2, 4, 6, 7 @44.1kHz > > becomes > > 0, 0, 2, 0, 4, 0, 6, 0, 7, 0 @88.2kHz > > this is then passed through a low-pass digital filter with a cut-off > > frequency set to the bandwidth of the original signal. The result > will > > be an upsampled signal with the same spectral content as the > original. > > Take both the original data and your list with zeros interspersed, and > > plot it using your favorite plotting tool. You will see that you are > adding a huge amount of very high frequency "signal" that is 100% > spurious. > To do a 0, 2, 0, 4, 0 requires extremely high frequency, and since real > > PCM is sinusoidal, it has to have -2, -4, or something close because > with sine waves, you have to have negative values to match the > positive, > unless you have a really big low frequency signal that takes something > > that is really > > 0, +1, +2, +1, 0, -1, -2, -1, 0, +1, +2, +1, 0, -1, -2, -1, 0, > into something that is positive for a long time. > > Anything that goes 0, 2, 0, 4, 0 has signals at least twice the > frequency of a signal that goes 0, 2, 4, ... > > This is all just Harry Nyquist and Claude Shannon's work. > > -- > Pat > http://www.pfarrell.com/music/slimserver/slimsoftware.html
Yes, but the high frequency content that is added by the zeroes can be shown to be an exact copy of the original content repeated at higher frequency. This is then removed by filtering to leave an upsampled signal with the same frequency content as the original. The key here is that adding zeros does not affect the frequency content in the bandwidth of the original signal, only at higher frequencies (above the nyquist frequency of the original data) and this is easily removed by filtering. -- Muggy ------------------------------------------------------------------------ Muggy's Profile: http://forums.slimdevices.com/member.php?userid=2258 View this thread: http://forums.slimdevices.com/showthread.php?t=32958 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/audiophiles
