"Audio Empire" wrote in message
...
On Wed, 7 Mar 2012 16:12:03 -0800, Arny Krueger wrote
Let's face it, digital filtering has improved to the point where such
humungeous (2 cotave) guard bands serve no purpose at all.
While digital filtering is , as you say, very good, the precognitive
nature
of the digital filter makes "pre-ringing" a condition that doesn't exist
in
analog filtering. If one were to use a high sample rate (say, 88.2 KHz),
then
It turns out that sharp-cutoff digital filtering can be tuned so that it has
pre-ringing, post-ringing, or anything in-between. These days most digital
filter parameters are calculated using sophisticated mathematical tools such
as Matlab. Worked out examples can be found he
http://www.mathworks.com/products/ds...lpfirdemo.html.
Digital Filters can be designed to be minimum phase, in which case there is
no pre-ringing at all, just like conventional analog filters. Commonly they
are designed to be linear phase or zero-phase which implies pre-ringing.
Digital filtering of many kinds is easily implemented with software and
applied to high sample rate digital audio files.DBTs have been done
comparing various approaches. The general outcome has been that the 22.05
KHz Nyquist frequency of Red Book audio is high enough that there is
already considerable margin, and the details of the filter design are fairly
non-critical.