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

Michael T. Dean mtdean at thirdcontact.com
Sat Aug 16 03:53:58 UTC 2008


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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