pippin wrote: > Um. Sorry. Again, I fail to see it. > Again: Why does interpolation filtering on the digital side improve the > analog filtering and how is the interpolation even correlated to your > desired filter response. > > I can find a lot of prosa about this on the internet, mainly by makers > of such filters, but I haven't found a single explanation that makes > sense. All I find is stuff like this: > http://www.ni.com/white-paper/5515/en/ > Which - sorry - is nonsense (the digital interpolation part. The analog > and imaging explanations are OK).
Hi Pippin Let's have a look at this. Without oversampling, the analog anti-imaging filter requirements are obviously difficult - especially for the audio passband and 44.1khz sample rate. With oversampling however, the analog anti-imaging filter requirements are relaxed, because now the stopband begins at the original Nyquist multiplied by the oversampling ratio. The images in-between have been low-passed by the digital interpolation/oversampling filter, the exact parameters and usual filter tradeoffs of which are by design. This is what Figure 4 is trying to show in your link. The interpolation algorithm can therefore be compared to an analogue low-pass filter but in the digital domain. Neither of these need to analyse an hour in advance to perform reconstruction of the complex musical waveform according to sampling theory, although you are quite right, more than the one preceding sample would be necessary to interpolate, as your pictures nicely show. Regarding noise: oversampling actually increases the SNR as quantisation noise is spread over a wider frequency range, further enhanced by noise shaping and sigma delta process. ------------------------------------------------------------------------ flimflam's Profile: http://forums.slimdevices.com/member.php?userid=56891 View this thread: http://forums.slimdevices.com/showthread.php?t=99088 _______________________________________________ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/mailman/listinfo/audiophiles
