[mythtv-users] .24 Audio results: mixed

Jean-Yves Avenard jyavenard at gmail.com
Fri Jun 25 04:41:42 UTC 2010


On 25 June 2010 14:19, Douglas Peale <Douglas_Peale at comcast.net> wrote:
> Switching to pulseaudio:default no longer causes a hang confirmed.
> Selecting "ALSA:iec958:CARD=Intel,DEV=0" still gets me noise for Dolby Digital signals

Nothing was changed here... did selecting iec958 ever worked ?

> Selecting "ALSA:default" still requires toggling the mute button in the mixer application to get digital pass through to work
> (though stereo signals always work).

Do you have to do it all the time, or just after a restart?

> Niggling little details:
> For output devices like HDMI and SPDIF, isn't the speaker configuration handled by the other end of the cable? (eg my receiver
> can handle multiple different speaker configurations, routing sound to the speakers I have regardless of the channels in the

It is.. But the SPDIF port will only report as supporting a maximum of
2 channels. As it's ALSA, you then know some device can support AC3
and DTS.

HDMI port will report up to 8 channels, so if you check the LPCM audio
will be sent as is once decoded. If LPCM isnt' checked and you are
trying to send multi-channels audio, then the audio will be re-encoded
as AC3 if needed.

Mythtv can't fully know what you have connected, but it can make
decision on what you won't need in the settings.

So if you select a SPDIF port, or something reporting a maximum of 2
channels: LPCM setting is not accessible.

With Pulse, I know for a fact that it doesn't support AC3 or DTS
passthrough, so I disable those options. Same with OSS

> input stream), so in the case of these outputs I'm really choosing between stereo and digital pass through rather than between
> stereo and 5.1. And when I select digital pass through, I am letting my receiver handle the routing of sound from input signal
> to speakers. I guess all I'm really suggesting here is change "5.1" to "digital pass through" in the drop down menu for Speaker
> Configuration when an HDMI or SPDIF output is selected.

It's handled differently, but the result is the same.

if you uncheck AC3 and DTS, you will see that the number of channels
will automatically switch to stereo on your system.
It knows that with SPDIF, unless you use AC3 or DTS you can't do 5.1

I can't unfortunately replace AC3 and DTS with one "passthrough
settings". There have been a few reports of people here with amplifier
that only supported AC3 or DTS, not both...

But I take into account your suggestion.
"5.1" could be displayed as "digital passthrough" or maybe "5.1
digital" if it is only available through AC3 or DTS..

> Audio output device selection box lists output device names. Unfortunately those names don't mean a whole lot to people
> unfamiliar with the Linux sound architecture. I am aware that if I select any of them, a description of that input shows up at
> the bottom, but there is lots of room in that drop down box to add a short comment after the name (perhaps after a "#" to
> indicate it is not part of the device name itself) that indicated the physical type of connector the device implied: analog,
> HDMI, SPDIF. This might help people select the correct device on the first attempt.

I see..

the problem is what it's this box, is what is going to be used explicitely...
Add extra characters that ultimately will required to be removed is
going to be a pain to handle

> A test button for each of the various "Audio Processing Capabilities" check boxes that would send short test signals of the
> specified types to the receiver would help people get their setup correct the first time.

That's on my to-do list ...

> Take the above as suggestions you can ignore if you want to, not demands. What you've done is a significant improvement over
> what was there. Thank you.

you're welcome..
I do think it makes configuration much easier, and I hope it will
prevent a fair share of the usual problems.

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