[mythtv-users] "Woodchuck" sound on TV playback

John Welch jrw3319 at gmail.com
Sat Aug 16 04:10:06 UTC 2008


On Fri, Aug 15, 2008 at 11:53 PM, Michael T. Dean
<mtdean at thirdcontact.com> wrote:
> On 08/15/2008 11:45 PM, John Welch wrote:
>> On Fri, Aug 15, 2008 at 10:49 PM, Michael T. Dean wrote:
>>
>>> On 08/15/2008 09:47 PM, Joshn Welch wrote:
>>>
>>>> One thing I'm curious about is step 6, where you say "turn on iec958
>>>> in alsamixer".  In my alsamixer settings I've got a regular volume bar
>>>> for IEC958.
>>> Are you sure it's a "regular volume bar" (as there's no such thing as
>>> volume when it comes to IEC958--the receiver, not the computer, controls
>>> the volume).  I'd bet it's a 4-state switch (i.e. has 4 "volume"
>>> settings: 0, 33, 67, and 100).  Each setting does something different.
>> Thanks for the reply Mike.  When I saw your message I thought it was
>> going to be the answer I needed to fix the problem because I do recall
>> seeing this type of "4-state switch" that you mention.  Sadly, I must
>> have been recalling a different system, because on the system in
>> question, strangely enough, the IEC958 setting in alsamixer, is in
>> fact a regular volume slider, and it does operate as such (ie if I set
>> it at 0 I hear nothing, and as I increase it the "static chatter" gets
>> louder.
>>
>
> Must be a softvol control (which, IMHO, shouldn't exist/be used).
>
> You may still have some sort of switch in there that's just in the wrong
> position.  Too many different CODEC chips to know them all, and my only
> experience with the intel-hda stuff is with cards that aren't fully
> working, yet, so...
>
>>> If the switch I mentioned above is, "IEC958 Playback AC97-SPSA," or
>>> similar, try setting it to 0.  On this particular switch, the 4
>>> positions are:
>>>
>>> 0 (=0)  : PCM1
>>> 1 (=33) : PCM2,PCM1(rear)
>>> 2 (=67) : Center and LFE
>>> 3 (=100): PCM3,Modem,Dedicated S/PDIF
>>>
>>> Sure, now you're thinking, "Well, wouldn't I want 3 for Dedicated
>>> S/PDIF," but you're not realizing that most all sound card (and mobo)
>>> manufacturers are too cheap to hook up the Dedicated S/PDIF.  Just trust
>>> me, if the switch is labeled, "IEC958 Playback AC97-SPSA," you want 0
>>> (unless you have a /very/ rare sound card with the S/PDIF connected (but
>>> then you want the "IEC958 Playback Source" set to something other than PCM).
>>>
>>> If the switch is labeled something different and it's a switch (i.e. it
>>> has a /very/ low resolution for a volume slider), you may need some
>>> other setting, but you'll have to play around or research it yourself to
>>> figure out which one.
>> In alsamixer the switch in question simply says "IEC958"
>>> Note, also, if you get everything set up properly and it still doesn't
>>> work, it may just be your receiver doesn't properly detect AC-3/DTS.
>>> You can figure out if this is the case by doing an "iecset rate 48000
>>> audio 0" while playing the "static" sound from Myth.  If it switches to
>>> real audio...
>> I usually have a different frontend connected to the receiver, and the
>> receiver does properly detect AC-3/DTS.  Also, attempting to run the
>> "iecset" command with the arguments you suggested gives me a
>> "snd_ctl_elem_write: Operation not permitted" error, even when I run
>> it as root.
>
> Ah.  It's not letting you change the parameters while the IEC958 is in
> use.  That makes this test kind of impossible, but it sounds like that's
> not the issue.
>
> Mike
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>
Thanks again Mike.  All the other switches/sliders seem to be analog
related, but I guess I'll keep plugging away.  Man, this stuff can be
frustrating.


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