[mythtv-users] Very poor picture quality from HD3000

Wed Sep 23 00:38:06 UTC 2009

First of all, thanks for trying to help me! 

Well, let me try to describe the picture that I am getting: 
It is fine for about a second and then it starts getting artifacts, blurring, green blocks, 
freezes, then it comes back for a second, then goes bad again. I get audio only during 
the "good" seconds, otherwise, no audio. My receiver (myth box is connect through S/PDIF) 
keeps switching between Dolby Digital (when there is good sound) and Pro Logic (the default) 

This happens on all channels that I have tried. On the other hand, the TV on the same channels 
with the same cable/signal gets good picture and sound. 

As far as the firmware, I just downloaded the firmware package from pcHDTV.com and diffed it 
against the firmware installed on the system and they were identical. 

I am in the Bay Area, California and I used the following settings for the frequencies and scans: 
General settings -> us-cable 
Input Selection->Scan for Channels->Cable-High and QAM-256 
The signal comes from the cable TV coax and not an antenna and I am scanning for all the channels 
from the Extended Basic Cable Lineup which Comcast switched to digital late last month (channels 
30-85 from the old Analog lineup). 

I am not sure whether that is correct but Cable-IRC-High seemed to produce the same results 
and Cable-HRC-High didn't find any channels at all. 

I should also mention that the HD3000 does not find all the channels that the TV finds. For most 
of the channels that are missing from the HD3000 scan, it (the HD3000) gets a lock but then it 
times out with "no tables". 

----- Original Message ----- 
From: "Brian Wood" <beww at beww.org> 
To: "Discussion about mythtv" <mythtv-users at mythtv.org> 
Sent: Tuesday, September 22, 2009 5:02:33 PM GMT -08:00 US/Canada Pacific 
Subject: Re: [mythtv-users] Very poor picture quality from HD3000 

> ----- Original Message ----- 
> From: "Brian Wood" <beww at beww.org> 

>> I know the signal strengths reported by some cards can be misleading, I've 
>> heard some cards do not really implement that feature, and indicate the 
>> same strength no matter what is fed to them. I'm pretty sure the HD-3000 is 
>> one of those, though it may have been the early drivers and not the card 
>> itself. 

On Tuesday 22 September 2009 17:23:02 voidtrance at comcast.net wrote: 

> The numbers are from the the little dialog that pops up in mythtv-setup 
> during the channel scan. Both signal strength and S/N are in percent. 
> It could be that the bar that represents S/N means db (so 13db, if that 
> makes any sense - I am not a signals guy) but the character after the bar 
> is '%'. 
> 

What does the picture look like? Are you getting blocking? Green blotches? 
What is making it "poor"? I understand it can sometimes be hard to describe. 

In the analog world a 13db. video (not RF) S/N would be unwatchable, but with 
digital RF TV signals it might well produce a usable result. The thing about 
digital is it looks great right up to the point where it becomes total crap, 
a "cliff" threshold. 

I think the cards that purport to tell you the S/N are actually using the BER 
(bit error rate) to approximate the S/N, which involves some assumptions, but 
is reasonable. 

How is the audio? Can you even decode it? 

I guess I can't ask you to get out your oscilloscope and tell me what the eye 
pattern looks like, but you should be able to get a usable picture from an 
HD-3000 if the signal looks OK directly into a TV set and you have >90% 
signal on the scan. I have got good pictures with approx. 55% on the scan. 

I assume you're using the latest firmware for the card? I haven't kept up, so 
I don't know what's current. 

I also assume you are using the correct frequency table for your source (cable 
or broadcast). 

The damaged frames you are getting certainly look like a signal problem, are 
we talking OTA or cable here (ATSC or QAM)? I'm assuming you're in the USA by 
your email address. 

-- 
Brian Wood 
beww at beww.org 
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