[mythtv-users] "Woodchuck" sound on TV playback
John Welch
jrw3319 at gmail.com
Sat Aug 16 03:45:17 UTC 2008
On Fri, Aug 15, 2008 at 10:49 PM, Michael T. Dean
<mtdean at thirdcontact.com> 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.
> 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.
Thanks for your help.
John
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