i use an hdmi to dvi to hook up my cable box to my 970 and an optical cable for sound. was working fine until recently.

been getting a hasty humm when i turn my cable box on. nothing but humm. i played with the cable box settings to output audio to HDMI setting from the Dolby Digital setting. I do not know why but it worked. No more nasty humm. but now i don't get dolby digital output anymore. what is going on? is the cable box messed up?

It's the cable box. Mine did the same thing one evening a month or two ago, and the only way to fix it was to disable the Dolby Digital output (force PCM stereo). I left it that way for a week or two and then changed it back, and all was well. Didn't even both complaining to Comcast, especially since the problem went away.

any idea what the cause of the problem is? software issue?
i just miss Dolby Digital output for now.

I don't know what it was, but my suspicion is a software glitch.

its probably a solder connection in the box. they buy those in massive amounts, i cant imagine motorola is really putting a high quality stamp on them.

most cable company's will replace their equipment for free, give them a call.

I could see that, but the fact that switching from one audio format to another fixed it (a change that happens solely inside a chunk of silicon, with the same digital audio pathway used for either setting) and the fact that the firmware on Scientific Atlanta's boxes is a bit of a mess to begin with make me think the problem was somewhere on the software side.

Gonk:

I would not be sure, I had a problem where two HD channels would not come in with any audio if I listened in Dolby Digital (both were CBS owned channels). What was bizarre was that the older analog versions of those channels came in just fine in Dolby Digital. I could not conceive that this was a box problem, but I eventually swapped DVR's for another reason and the problem mysteriously disappeared.

The analog versions were coming in as Dolby Digital 2.0, which is a separate mix entirely. I've seen cases where a local affiliate screwed up the HD audio feed while getting the SD audio feed right. Thankfully that's less common now that more people are actually watching the HD broadcasts, as they get lots of calls if they mess things up too bad. I doubt that a hardware fault would affect just those two HD stations. It was most likely either a firmware glitch in the first unit or a broadcast error that got fixed at around the same time as your DVR box swap.