The cable card is looking at the analog channels natively and tuning them directly for display on the TV. The DVR has to encode the analog video in order to spool it to the hard drive for buffering. When you watch TV through the cablecard you are watching realtime television. With the DVR you're watching delayed video as it takes time to encode the video, write it to the drive, and then finally read it off the drive for viewing. Also if the DVR is not a series III 6412/6146 is doesn't have the more advanced chipset that resolves some of the video encoding artifacts generated by the encode/decode process.
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