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

Jay R. Ashworth jra at baylink.com
Wed Sep 5 01:43:55 UTC 2007

On Mon, Sep 03, 2007 at 11:49:16PM -0400, Daniel Kristjansson wrote:
> > > 4, 11, and 72.  :-)
> > OK, not likely a freq table issue.  :(
> FYI The other reason channels can be off is because cable operators
> are supposed the shift the frequency of any channel interfering with
> other regional broadcasts up or down a bit.

IRC and HRC, yes.

> Most analog tuners have a PLL that locks on to the visual carrier
> frequency. So the frequencies in MythTV for analog tuners is actually
> the approximate location of this visual carrier. Unfortunately the most
> popular tuners for computers, the Conexant CX and BTTV chip families,
> do not appear to not be very good at locking onto the VC so you need
> to give it a pretty close estimate. Also the resolution is only 62.5kHz,
> this low resolution is not common to all tuners, which is why MythTV
> uses exact frequencies now instead of the closest BTTV chip tunable
> frequency. When there is a good PLL using the correct frequency will
> only mean a slightly faster tune, when there isn't using the correct
> frequency will mean a better picture.

But there's no way to extract the PLL offset -- much less the AGC
level, so you could figure out if your signals are twisted -- from the
tuner, right?

> > > Sure, but again; not interactive.
> > Right.
> It's supposed to be interactive, the vagaries of hardware
> implementations may mean this is not the case, or there may
> simply be a bug.

It *is* supposed to be interactive?

What keys am I supposed to press in LiveTV to adjust it?

-- 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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