At Sat, 04 Oct 2003 15:39:52 +0100,
James Courtier-Dutton wrote:
>
> Hi,
>
> With 5.1 channel sound being used quite a lot now, I was wondering what
> to do about volume controls.
> For example, I have: -
> Front speakers controlled by PCM and Master slider.
> Rear speakers controlled by Surround slider
> Center controlled by Center Slider
> LFE controlled by LFE slider.
>
> I would assume that a "Master" slider would control all 6 channels at
> the same time.
> So, in this setup, the Master slider is not actually acting as a Master,
> but instead, only a Front speaker control.
>
> I suggest that in these cases, "Master" gets renamed to something else,
> and then alsa-lib takes over providing a "Master"
> alsa-lib could then also use config files, to define the mixer elements.
> We could then provide mixer elements that do proper "Master",
> "Front/Rear Fader" etc.
i agree with this idea.
the term "Master" is misuse in this case.
"Front" sounds more reasonable.
> I know you said earlier that you are in the process of developing a
> better mixer, possibly having 0db points etc.
> Could you add these suggestions, so that they are possible as well.
>
> Another problem I have come across, is that some sound cards have a
> headphone amplifier on the front speaker output, and some sound cards
> have a headphone amplifier on the rear/surround outputs.
> E.g. ALC650 has headphone on front output.
> AD1985 has headphone on surround (but is switchable to front).
> Does anyone know if the AC97 standard is headphones on front, or
> headphones on rear/surround ?
no standard. it depends on the implementation.
on the recent AC97 codecs, the headphone is no longer headphone, but
it means "true line-out" for the consumer devices. sigh, this change
is the real confusion! ac97 spec recommends the detection by the bit
flag in the RESET register and ac97 revision, but in fact, the
hardware vendor sets the old bit for the compatibility reason. grrr.
anyway, on AD198x, most devices use the SURR/HP_OUT for the front
output, and in fact, alsa driver swaps the outputs as default.
i'm thinking whether this switch should be provided in control API,
too, so that user can switch the behavior if the device is not
auto-detected.
> I was talking to a user who has sound coming out of a speaker output,
> but not the headphone or center/lfe outputs, also the slider name
> controlling the speaker output was "surround".
on AD1985, now "ADI-compat" mode is set as default. on this mode, the
volume control is assigned to "headphone" rather than "surround".
(hey, another confusion :) the "surround" effect seems appearing if
this mode is not set ("AC97-compat" mode), which is used still on
AD1980.
on ADI-compat mode, "headphone" and "master" do play really as the
"master" volume. there are DAC attenuations in addition.
in this case, we should control both "master" and "headphone"
(i.e. register 0x02 and 0x04) as a single "master" control, IMO.
> It would be nice to find out from yourselves what the AC97 standard says
> it should be, and I will then post a PATCH to get the AD1985 to act in
> the same way as all other sound cards.
Takashi
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