[pulseaudio-discuss] [PATCH 2/3] alsa: Default to 30% in absence of sink hw volume

[Alexander E. Patrakov]

01.12.2014 19:03, Tanu Kaskinen wrote:
> You didn't explain very thoroughly why 100% would be the best default
> for digital outputs. You mentioned that the volume should by default be
> the same for passthrough and non-passthrough. That alone doesn't seem to
> be a good enough reason to default to full volume, however, because if
> the full volume is way too loud, then the full volume should be avoided
> in any case. Passthrough is a special case that shouldn't drive the
> design to the extent that the common cases become broken.

The "full volume is way too loud" argument is only valid for headphones, 
built-in speakers and similar analog devices which don't contain their 
own non-PC-controlled volume control and thus rely on the volume control 
inside the PC. All digital outputs are eventually connected to a TV or a 
receiver that does have its own hardware volume control.

The passthrough argument is here because, for passthrough content, the 
computer-based volume control is ineffective, i.e. passthrough content 
is played at 100% volume by definition. Also, if other signal sources 
(like a hardware BluRay player) are used, they also either output 
passthrough content or PCM content equivalent to what a PC would output 
at 100% volume. And then the volume control in the receiver attenuates 
that to a sane level.

So, if such signal sources (hardware players, passthrough content) are 
used at all, the hardware volume control (in the receiver) is set to the 
value which is comfortable for such content. It would be natural to 
expect that this value should be useful for non-passthrough content, too.

> That said, I believe the digital outputs are typically associated with
> another important property: the existence of an extra volume control
> between the sound card output and the speakers. If that's the case, then
> I think it's a good idea to default to 100%, because the extra volume
> control is likely going to limit the output to a sane level. I have
> extremely little personal experience of systems that use digital
> outputs, but it seems to me that such systems are very likely to have a
> separate volume control - I haven't heard of direct-to-speakers hardware
> with digital input that wouldn't have volume control.

Exactly.

>
> This "separate volume control" logic applies to analog outputs too in
> theory, but in practice we never know with analog outputs whether
> there's a separate volume control or not.
>

Right.

-- 
Alexander E. Patrakov