[alsa-devel] 2 speakers are assigned to the same DAC, this can't support 4.0/2.1 channles

[Raymond Yau]

 OK, good to know. I'd like to test a bit more via hda-emu whether this
>>> gives any ill effects. So far, this seems fixing a few other machines, too,
>>> so it's a good thing to have in general.
>>>
>> This change alone results in regressions on machines that are capable
>> of 4.0/5.1 surrounds.  For avoiding it, the badness for multi-io has
>> to be increased as well.  It's damn sensitive.
>>
>> But, now I wonder now whether blindly applying this is good.  Suppose
>> a machine with 2.1 speaker and one headphone, but the codec has only
>> two DACs.  With this setup, now the headphone and the speaker share
>> the same DAC, as the cost of having individual 2.1 speaker volume.
>> Is this more useful than having individual volumes for speaker and
>> headphone?
>>
>> Maybe the machine you're trying to support has a different situation.
>> So applying the new rule to limited devices is fine.  But if so, it's
>> not necessarily to be an adjustment of badness table, but just you can
>> provide the simple DAC/pin preference map explicitly in the fixup.
>>
>
> Oh, this is an interesting trade-off.
>
> In the PulseAudio desktop scenario, we automute the speaker, and
> PulseAudio remembers the individual headphone and speaker volumes. So in
> this case, there is no benefit from having individual headphone and speaker
> volume at the ALSA level.
>
> However if a user wants to turn off automute, then there is a need for
> being able to adjust headphone and speaker volume individually.
>

Do "front Playback volume" a good name when volume control is shared by
headphone and speaker" ?

in desktop with alc66x , volume control shared by headphone and Line Out is
name as "Front" because it support 5.1

>
> But it's not just a question of volume control for 2.1. Being able to send
> a different stream to the subwoofer could be useful too, especially if the
> hardware filter is bad or non-existing.
>

when subwoofer is using stereo pin complex (usually with 6, 8 or 10
channels codec), only one left or right channel is used (e.g. Asus N series
note book external sonic master subwoofer use right channel but acer aspire
5930g internal subwoofer using left channel

FL, FR LFE N/A
FL, FR, N/A, LFE

how do pulseaudio perform lfe filter when subwoofer is using mono pin
since the downmix widget mix left and right channel and scale down the
volume ?

FL, FR, LFE, LFE

do it need more CPU than those use one channel of stereo pin complex

For those 2 channel hda codec 's subwoofer must use mono pin

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