How is that proved ?
I don't see you got the point: DTV is sending down to STBs over-compressed SD stream/signal with REDUCED resolution to 480x480 or 352x480 instead of 704x480 what OTA station providing for normal (not sub-channels) SD signal.
How dare of you to discard the facts ?
While its certain that DIRECTV actually down-rezes SD channels this way in addition to MPEG (over) compression P. Smith, how do you know that OTA broadcast stations down-rez SD and then heavily compress on their secondary sub-channels in a likewise manner?
I know the broadcast stations obviously use a high compression on any secondary SD sub-channels what with only a 19.3 mb/s total bit rate to work with and not wishing to really infringe upon their main HD sub-channel. But I wasn't aware of any standard practice of down-rezing of the original source material before compression as DIRECTV does.