[mythtv-users] Realtime Fine Tuning -- just a pipe dream?

Jay R. Ashworth jra at baylink.com
Fri Aug 31 20:03:45 UTC 2007

On Fri, Aug 31, 2007 at 03:39:07PM -0400, Michael T. Dean wrote:
> On 08/31/2007 03:08 PM, Jay R. Ashworth wrote:
> > Has the ability to adjust channel fine-tuning from LiveTV (permanently
> > for a channel, obviously) ever been anything more than a Feature
> > Wishlist entry?  I've almost never needed it, but on my sis's recently
> > reworked box, 3 channels are semi-ugly, and I was trying to see why.
> What three channels/frequency ID's (and what TV source--i.e. cable)? 
> There may be an even easier fix.  That sounds a /lot/ like a frequency
> table issue.

4, 11, and 72.  :-)

> In theory, fine-tuning should never be required for any channel.  The
> tuner's hardware fine-tune mechanism should be more than enough for
> variations from the spec--the resolution of the kernel's tuner module is
> (currently) only 62.5kHz.  (And the values you specify for finetune are
> in kHz, so unless the value you've chosen is high, you may not even be
> affecting the value passed to the tuner module--though it all depends on
> the specific frequency and rounding issues.  This doesn't mean you
> wouldn't see a difference as there are temporal variations and the state
> of the tuner before retuning can impact the end result.)

Sure.  But it's a lot easier to tell if you don't have to
change->save->retune->retune again...

> > I tried using the Channel editor page on MythWeb, and that knocked the
> > backend over; I gather that's a known problem in 20.1.
> >
> > I succeeded in using PHPMyAdmin to do it, but it's a much taller pain
> > than just using '<' and '>' on the keyboard...
> The mythfrontend channel editor also allows you to specify a finetune
> value (which is, at least, safer than direct DB edits).

Sure, but again; not interactive.

> > I'd be happy to write a patch myself, but I'll probably need some
> > pointers...
> There's nothing in there now.  As a matter of fact, due to the
> implementation of the tuner hardware, most likely--to truly be able to
> test the new finetune value--you'd have to switch to a channel that's
> far-enough separated from the current channel (frequency-wise--which
> doesn't necessarily correspond to channel numbers) and possibly even to
> a channel in another band (depending on tuner hardware--and bands,
> themselves, are tuner specific) and then change back to the channel
> whose finetune you're testing.  So, > would result in two channel
> changes, then the next > results in two, ...  The hardest part would be
> figuring out what "other" channel to use when testing the current
> channel's finetune.

Hmmm.  Sounds like the tuner phase-locks to the carrier it finds, and
finetuning doesn't do much of anything.  Although that doesn't match
what I actually observed, so I'm probably wrong.

Can you spare me two more sentences on *why* that procedure would be
necessary, and whether it's true of all tuner modules?

-- jra
Jay R. Ashworth                   Baylink                      jra at baylink.com
Designer                     The Things I Think                       RFC 2100
Ashworth & Associates     http://baylink.pitas.com                     '87 e24
St Petersburg FL USA      http://photo.imageinc.us             +1 727 647 1274

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