Reg Edwards wrote:
How much, if any, is digital filtering better than the old-fashioned Xtl
filter.

What makes DSP filtering better than Xtal filters is that it is
programmable, not hardwired. The parameters of a DSP filter are
continuously variable although not usually implemented that way
in most amateur radio receivers. Given the processing power
necessary for a filter, one can theoretically have any of a
near-infinite number of filter configurations.

Reg, you could probably program a DSP audio filter that runs on
a PC and outputs audio through the sound card like the ClearSpeech
speaker systems. PSK-31 software packages for the PC certainly contain
a number of DSP filters and other DSP algorithms.

Note that Digital Signal Processing is not limited to filters.
--
73, Cecil http://www.qsl.net/w5dxp