[mythtv-users] Why is my 350's audio so much l-l-louder! than the 250's?

[f-myth-users@media.mit.edu]

I just noticed a peculiar situation:

Running 18.1.  MBE has several 250's with ivtv 0.4.1-r1.  SBE/FE has
1 350 with ivtv 0.4.0.  LiveTV uses the 350 because I have "avoid
conflicts" checked and the 350 is in the FE.  Cable feed is split
across all of them into their RF inputs.  Everything is getting
played back through the 350's AV output, and the 350's audio out
is looped through my sound card and then to the TV.

If I leave all the sliders in the recording profiles for Default/
LiveTV/High/Low quality at 90% (the default), and then start recording
on all tuners on various channels, whatever the 350 is recording has
MUCH louder audio (6-9db, as measured by my trusty dB meter) than the
250's.  If I have the Master and PCM sliders in general setup set to
90%, then on my equipment, this happens to mean that anything on the
250's plays back somewhat quieter than direct to the TV (I can
dual-screen the TV and flip back and forth between direct from the
cable feed or through the Myth box), while the 350 plays back somewhat
louder.  If I raise the Master & PCM sliders to 100%, then the 250's
essentially play back at the level of the direct-to-TV path, but then
the 350 is playing back MUCH louder.  (When I say "playing back", of
course, I mean "when I play back a stream that was captured by that
card.")

This is true for the 350 regardless of whether I'm using it in LiveTV
mode, or it's capturing just like the rest of the tuners for a
scheduled recording.

I can't just lower the slider for LiveTV and leave it at that, because
I'd like shows recorded by the 350 to have the same approximate volume
as those recorded by the 250's.  Yet I can't seem to find any independent
volume control per-tuner, and I don't understand why this one card would
be capturing as such a high level anyway.  (And if I raise all the
sliders in the recording profiles to 100%, the 250's still give me
reasonable audio---just somewhat louder, of course---while the 350's
audio is so hot that it's clipped and objectionable.)

Is this a well-known effect?  Is it peculiar to 350's vs 250's, or
between ivtv 0.4.0 and 0.4.1-r1?  Is there some register I should be
setting on the 350 or something?  I -could- try installing 0.4.1-x or
even 0.5.x on the 350, but I'd rather leave well enough alone unless
it's likely that this will fix it, since I had problems a while back
with sporadically vanishing audio on ch2 and would rather not disturb
the situation and possibly wind up back there.

[Btw, ivtvctl -Y reports "volume = 58950" for both the 350 and the
250's.  By trial and error (switching between LiveTV's output and the
TV's direct input from cable), I find that "ivtvctl -y volume=54000"
on the 350 normalizes its audio level to that of the TV; I'll have to
play around a little more to make sure that also means it's normalized
to the 250's.  But why should I have to adjust this down so much?
(And it won't stick!  Changing channels or leaving LiveTV is fine,
but reentering LiveTV bashes the register back to 58950!  Is there
any way to make this stick, as a workaround?)]

Thanks for any insights.

(Unfortunately, swapping the 350 into the other machine just to test
ivtv versions w/o reinstalling anything would probably be a fairly
large pain, given that I'd have to schedule up some recordings in
advance, let it go, and then swap back to see how they went---and
because the machines are both headless unless you count the 350.
So I'd rather not swap hardware if there's another way to debug.)