[mythtv-users] Summery of my problems

Michael T. Dean mtdean at thirdcontact.com
Sun Jan 29 02:05:51 UTC 2006

On 01/28/2006 08:29 PM, Rudy Zijlstra wrote:
> Michael T. Dean wrote:
>> On 01/28/2006 12:46 PM, Dylan R. Semler wrote:
>>> Michael T. Dean wrote:
>>>> On 01/27/2006 01:07 AM, Robert Johnston wrote:
>>>>> On 1/26/06, Dylan R. Semler <dsemler at macalester.edu> wrote:
>>>>>> For analog, the picture quality is pretty bad (noisy)...  The 
>>>>>> picture quality is much better using tvtime and those lines do not 
>>>>>> appear.
>>>>> As for the noise, make sure that Myth is tuning into the same
>>>>> frequency (EXACTLY the same frequency) as TVTime is. It sounds like
>>>>> Myth's off by a few Khz.
>>>> Being off by a few KHz shouldn't matter.  Many of the NTSC cable 
>>>> channel frequencies are off by 12.5 KHz (and the same goes for IRC, 
>>>> and HRC varies by 5-15KHz), but the tuner hardware's fine-tuning 
>>>> mechanism should still be able to find the appropriate center 
>>>> frequency.  See 
>>>> http://www.gossamer-threads.com/lists/mythtv/dev/164614#164614 
>>>> (which was totally ignored by the guy complaining in Trac that the 
>>>> frequencies are off) for an in-depth listing of what frequencies are 
>>>> off and why it shouldn't matter.
>>>> If you (Dylan) want to try an academically-correct list of frequency 
>>>> definitions, I'd be happy to create one for you (against SVN--just 
>>>> let me know which frequency list you're using: ntsc_bcast, 
>>>> ntsc_cable, ntsc_hrc, ntsc_irc (I'm assuming NTSC based on your 
>>>> e-mail address)), but you'll have to do all the testing because I 
>>>> don't have any RF-modulated sources.
>>> Well it's worth a shot.  I'd love to get better picture quality.  I'm 
>>> using ntsc_cable.
>> OK.  Attached is a patch...
>> If there really is a 
>> difference (and I still don't think there will be)

Read this ^^^^

> probably good to improve, but....
> for the silicon tuners i know about, (which are both the ones we use on 
> our products as well as some others), this makes no difference at all. 
> Most modern (silicon) tuners are able to finetune to the correct 
> frequency if the initial frequency is within 125KHz of the correct 
> frequency.
> We make use of this is the scanning algo, as this makes it possible in 
> Europe to scan with 250KHz steps in case we have to do a frequency sweep....
> Please keep in mind, Europe cable does not have any standard to adhere to.
That's what I've been saying all along--since someone mentioned that the 
frequency might be off by a few kHz...  However, it's hard to convince 
people it's not a problem if they can't test it for themselves...  ;)

Personally, I don't think it's worth changing the definitions in the 
source, but between the "This is so trivial to fix that it's silly not 
to." comment in Trac ( http://svn.mythtv.org/trac/ticket/610 and my 
response http://www.gossamer-threads.com/lists/mythtv/dev/164614#164614 
), and "common wisdom" about using the finetune values to adjust 
frequencies by a few kHz (which is often suggested), I figured a patch 
on the list that lets people see for themselves that it doesn't matter 
would be the best way to get other people to see it my way.


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