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

Michael T. Dean mtdean at thirdcontact.com
Fri Aug 31 19:39:07 UTC 2007

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.

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.)

> 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).

> 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.


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