Jim Lesurf wrote:
In article , Rob
wrote:


That's really why I ask - I think. If there's more than one way to
downsample properly, I'm stuffed.

In principle 'downsampling' should be done 'properly' and will then lead to
a uniquely defined results - even if done in various algorithmic ways.


That's not so.

Downsampling always involves a reduction in Nyquist frequency. It's
necessary therefore to filter the input to make sure frequencies above
this are sufficiently reduced. That filter can never be perfect, and
there will be various tradeoffs, involving extra loss of top-end,
in-band ripple and 'wrap-around' garbage from insufficient rejection of
higher-than-Nyquist signal. It's all down to what the person doing it
thought would be best (by some arbitrary criterion), and there is no
unique or 'right' answer.

--
Mike Scott (unet2 at [deletethis] scottsonline.org.uk)
Harlow Essex England