[pvrusb2] HVR-1950 - bad video quality

[Mike Isely]

On Fri, 3 Apr 2009, stan schultz wrote:

> So,  Let's back up a bit..  Remember, I can get WinTV to provide good
> reception.  That implies that the WinTV guys are setting at least one
> parameter on the card differently than pvrusb2.  So,  If that's the case,
> can I initialize the device with wintv and then plug it in to the linux box
> and not have the parameters mucked with?  Then I can read them with the
> /sys/classes interface and see what's different.  Will that work, or does
> the driver initialize everything when the device is plugged in?
> 
> Stan

It can also mean that WinTV is using a proper frequency table.  The 
"frequency table" is a map associating channel numbers to frequencies; 
it is something totally outside the driver and up to the application.  
All the driver knows is the frequency to which it has been tuned; the 
"table" such as it is, is in the application only.

The fact that it worked for you in WinTV is evidence that the hardware 
is good, you have a good RF connection, and you have a strong signal.  
But you don't know how WinTV tuned the device.  This is why I was 
suggesting trying an app that can do a thorough scan.

Answering your specific question, no you can't initialize it with WinTV 
and then move the device to the Linux box to examine the settings.  As 
soon as you plug it into the Linux box, the device will be completely 
reinitialized.  There's just simply no way around that.  (Yes, I know 
that the FX2 firmware can be manually extracted using that trick, but 
that is a very notable exception and the one thing that the driver can 
deliberately avoid initializing.)

Unfortunately if this really is a frequency table issue, it's something 
that is entirely outside of the pvrusb2 driver and I can't help you.  
Right now that seems like the most likely cause.  However (1) you are 
the first person in a very very long time to have issues like this, and 
(2) it is still conceivable that the v4l-dvb tuner module is doing 
something wrong - but if that were happening there should be a chorus of 
complaints here and so far you're the only one.  So I'm still thinking 
it's a tuning problem due to a wrong frequency table in your app.  Thus 
the reasoning for my response below.

  -Mike

> 
> On Thu, Apr 2, 2009 at 11:13 PM, Mike Isely <isely at isely.net> wrote:
> 
> > On Thu, 2 Apr 2009, stan schultz wrote:
> >
> > > So I got the camcorder out, plugged it into the composit input and the
> > > picture from it looks great.  As you said, that points at the tuner.  A
> > > couple searches showed there is all kinds of discussion about bad uscable
> > > table entries in mythtv. But I couldn't find anything truely useful.  I
> > > tried modifying the values in
> > /sys/class/pvrusb2/*/ctl_frequency/cur_value,
> > > but didn't really see a positive difference ever.
> > >
> > > Any Ideas?
> >
> > Well I only do over-the-air here, no cable, so I don't have a good basis
> > for comparison with your situation.  So I don't know how good / bad
> > MythTV is going to be when tuning cable.  Obviously the pvrusb2 driver &
> > hardware is not going to "care" where the signal is coming from so long
> > as the signal is coded following the standard it is configured for and
> > that it knows the right center frequency to tune for it.
> >
> > In your shoes I might consider trying something that can instead
> > directly scan all the possible frequencies itself.  I think a long time
> > ago I did this once with xawtv - the scantv part of the app IIRC can be
> > told to creep through the frequency spectrum with very small increments,
> > much higher granualarity than what would normally be required.  This
> > might allow you to have a fighting chance at least to figure out the
> > right frequencies.
> >
> > If the issue is not so much the correct frequency table but just finding
> > the right channels in the table, then you should try an app that can
> > simply do a scan.  Again, xawtv can do this.  (And so can MythTV.)  If
> > you try xawtv, please be aware of its caveats - the largest of which is
> > that I don't think it's in active development anymore.  The pvrusb2
> > driver's usage web page has additional important details about setting
> > up and using xawtv:
> >
> > http://www.isely.net/pvrusb2/usage.html#V4L
> >
> > Obviously you still want to use MythTV, but if you can get another app
> > to tune the hardware properly then you can at least rest assured that
> > the hardware and the driver are correct - then you can focus your
> > attention on getting MythTV to behave correctly.
> >
> > Here's another wild idea:
> >
> > http://home.arcor.de/saedelaere/index_eng.html
> >
> > I'm not sure if Christian (the author) is going to suddenly want a huge
> > pile of attention, but he's been talking to me about this app he's been
> > writing.  It's called "TV-Viewer".  Essentially it's a nice looking gui
> > that builds a TV app out of other building blocks.  I tried his 0.8b1
> > version a few days ago and it looks very slick.  I only mention it here
> > because it's capable of doing a channel scan.  You might want to give it
> > a spin...
> >
> >  -Mike
> >
> >
> > --
> >
> > Mike Isely
> > isely @ pobox (dot) com
> > PGP: 03 54 43 4D 75 E5 CC 92 71 16 01 E2 B5 F5 C1 E8
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-- 

Mike Isely
isely @ pobox (dot) com
PGP: 03 54 43 4D 75 E5 CC 92 71 16 01 E2 B5 F5 C1 E8