David Ward wrote:
On 06/08/2009 12:31 PM, Steven Toth wrote:
Your SNR is very low, 0x12c is 30db. I assume you're using digital
cable this is borderline.
Oh okay ... I wasn't sure how to translate those values before.
I like my cable system at home to be atleast 32db (0x140) bare
minimum, it's typically 0x160 (36db) for comfort.
In your opinion, would I have enough justification for asking Comcast to
increase the signal strength coming to my house? I'd like to avoid
calling someone to come out to my house to say "your TV works fine,
what's the problem?" and get slapped with a repair fee. I wasn't sure
how well I could trust the SNR values reported by the card either... I
wish I had a meter or something to test it on my own. When I move the
computer directly to the input for the entire house, I get an increase
of about 0.1dB.
No idea, I debug my own cable network issues. That being said, usually cable
companies like to deliver 0db to the house which is nice and hot, then it gets
split and energy loss occurs 9as well as noise injection). I usually take home
some metering equipment from the office to sweep my home network.
FYI, the signal strength is about 1dB higher for clear QAM signals.
(The values I sent are for ATSC.)
It's possible that the tuner and 1409 driver are a little more
optimized under windows.
How much attenuation can you add under windows with signal loss? It's
probably reasonably close to the edge also.
I tuned to the same channel under Windows, and I used the Signal
Strength Indicator application from Hauppauge (downloadable under the
Accessories page in the Support section). It's reporting a SNR of 29-30
dB, and the value for 'correctable' errors goes to a single-digit value
about every 5 seconds -- following the same pattern seen with 'azap'.
However, the difference is that 'uncorrectable' errors stays at 0.
Under Linux, it seems that all errors are 'uncorrectable'.
So you don't have much leg room with windows either, certainly not enough for my
liking. The difference between zero errors and a small handful can be pretty
small in RF terms.
Does the error correction occur in the driver or in the chipset? Seems
to me like maybe error correction is either not enabled or not
implemented correctly by the driver?
Error recovery is done in the chipset and is only as good as the RF signal
reaching the demodulator.
I agree that the SNR could be better, and if you think it is worth a
try, I'll see what Comcast will do. However, because Windows and my TV
work almost flawlessly, the Linux driver would ideally handle the
signals at least as well as them...
No idea and no I don't agree, just because your TV works doesn't mean the Linux
driver has to be reliable. That's wishful thinking on your part and Comcast are
not obliged to make your TV tuner work.
Again, if you have 29-30db on Windows you don't have a lot of legroom for signal
attenuation before you'll see errors. I frequently had windows reception
errors when running at 31db with some boards.
We're getting into the realm of 'do you need to amplify and/or debug your cable
network', and out of the realm of driver development.
Is the mxl5005s Linux tuner driver perfect? Is it as good as windows? Not quite,
but it's good for many people and it's unlikely to improve in the near future.
Try installing a decent cable amp. Try looking at the MythTV wiki and support
sites for improving your cable network.
Let me know what else is helpful from me, and thanks again for your help.
David
No problem, your welcome. I hope this advice helps.
Regards,
--
Steven Toth - Kernel Labs
http://www.kernellabs.com
--
To unsubscribe from this list: send the line "unsubscribe linux-media" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
