Hi STx and Peter,
just to add a few extra bits.....Totally agree with your comments STx about "Out of band signals"
Although the hi-fi purists will disagree, as you say, Really Low end Roll off, of the 30Hz end
is important, not just in broadcast, but in Live music systems, like for Bands and disco type use
Vital for large Valve audio power amps, either in valve TX's, or large valve audio amps for reggae

A basic RC Filter on its own for bass, the lower in freq, that you go, the more lift it produces
A basic Shelving filter is better, as this increase at sub bass freqs is reduced
but best way, is a Peaking bass filter, with adjustable "Q" (same meaning as for RF coils)
as this helps the Sub-sonic filter, to stop excessive 30Hz from being brought up
Processors (including the DSPX) have a bass peaking filter, as a pre-equalizer before the multiband

Very impressed by the Ixworth SDR, especially the broad frequency range it covers, sensitive as well
right from below the Radio code Clocks 60khz and German one on 77.5khz, right up to 30 Megs
Can even see Loran C at 100kc as well, but goes even lower than that, give it a try

Rod Watts