On 05/22/2013 09:44 PM, John Rigg wrote:
this comment raised my eyebrows a little bit. can you explain what you
mean by "decimation filter"? the way i understand it, decimation means
chopping off bits, usually by shifting the data words, and possibly
adding dither. how can this be a problem at fs/2? no new frequency
components are introduced (apart from additional quantisation noise,
which must necessarily be band-limited to fs/2), and the input of the
decimation stage will already be band-limited as well.
otoh, if you mean sample rate down-conversion, i understand your
comment, but then you picked an unfortunate term.
moreover, i'd expect src circuits with only -12dB at fs/s to be unusable
in practise, because the aliasing artefacts would be obvious. it means
the top octave from 10-20hkz would be polluted with junk at -24 to
-12dB, unless of course there are some oversampling tricks going on and
the effective fs is higher during down conversion. although i must
confess i don't know anything about DAC and SRC design - if someone can
explain this in more detail, i'm all ears.
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