On Mon, Jun 8, 2009 at 4:20 PM, Steven Toth <stoth@xxxxxxxxxxxxxx> wrote: > 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 > Steven, One thing that is interesting is that he is getting BER/UNC errors even on ATSC, when he has a 30.2 dB signal. While I agree that the cable company could be sending a weak signal, 30 dB should be plenty for ATSC. Also, it's possible that the playback application/codec in question poorly handles recovery from MPEG errors such as discontinuity, which results in the experience appearing to be worse under Linux. I'm going to see if I can find some cycles to do some testing here with s5h1409/s5h1411 and see if I can reproduce what David is seeing. Devin -- Devin J. Heitmueller - 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
