4 Feb
1999
4 Feb
'99
3:45 p.m.
Philip asks about his analog oversampling filter:
So why does this sort of analogue filter not reduce
the sampling noise at
Fs/2?
Because it is effectively a lowpass filter with a passband extending to Fs/2.
It may attenuate the signal at Fs/2 slightly, but not enough to be useful.
The sampling noise needs to be attenuated by at least 60 dB for something that
would be marginally acceptable as a cheap consumer CD player, and well over
100 dB for audiophile equipment.
I'll confess that I'm NOT an expert on this stuff, and it's been over ten
years since I did any serious study of it, so it is possible that I'm
mistaken. I don't currently have time to set up a simulation to test the
hypothesis.