[LAU] digital volume sounds better at 0 dB?

[Robin Gareus]

On 06/19/2010 01:57 AM, Bearcat M. Şandor wrote:
> On Fri, 2010-06-18 at 22:41 +0200, fons at kokkinizita.net wrote:
> 
>> The meters are probably completely useless.
>>
>> The chip used in your soundcard has a digital gain control
>> with a range of 0...-120 dB in steps of 0.5 dB. Does that
>> correspond to what alsamixer is showing ? If not you'd
>> better leave the gain at 0 dB.
>>
> Alsamixer reports "dB gain 0.00, 0.00" to -60.00, -60.00 in .5 dB steps.
> Does that correspond to -120 dB somehow (both channels == 120 dB total)?
> (i'm a newb at all this)

No it does not add up that way. Maybe alsamixer is showing wrong
numbers?! Fons may know more.

>> If that soundcard really has the dynamic range that the
>> sales blurb claims it has, then its output level will be
>> a lot higher than what is expected by the average non-pro
>> amplifier, including 'audiophile' ones.
>>
>> That means that you should turn down the power amp gain
>> quite a bit.
> This is a low powered 10 watt max amp (class t chip)
> 
>> The correct alignment procedure would be:
>>
>> 1. Play a piece of music representative of what you 
>> normally listen to. Check the digital level with e.g.
>> jkmeter, For classic use the K20 mode and ensure you
>> have a level around 0 dB. For pop use the K14 mode
>> and again ensure you have around 0 dB.
> I compiled and started up jkmeter, then figured out how to output to it using qjackctl. 

Welcome aboard.

> The alsamixer volume controls make no difference at all to jkmeter, but adjusting the
> volume on mplayer does. Is this the expected behavior? 

Yes it is. Alsamixer controls the volume in the mixer of the sound-card.
JACK is all in software. Consider the following (somewhat simplified)
diagram:

  JACKified-audio-app
(eg mplayer, ardour, jkmeter)
         |
         v
     JACK-server
         |
         v
     Soundcard  ## hardware-mixer controlled by alsamixer
         |
         v
   Amp & Speakers

When you adjust the volume in mplayer, mplayer itself scales the volume.
mplayer does not interact with the soundcard's hardware-mixer. (Well,
you can configure mplayer to do either or both, but the default with
mplayer/JACK is to use mplayer's integrated "amp".)

jkmeter (or any other JACK app) gets mplayer's audio directly from JACKd
without the audio-data going to the soundcard first.

> I was not sure how to activate K20 or K14 given 
> jkmeter's interface.

You need jkmeter version >= 0.4.0.
Run `jkmeter -type k14` to get the K14 scale (k20 is the default)
`jkmeter -h` prints usage and version information.

Information on the K-system can be found in jkmeter's README and at
http://www.digido.com/level-practices-part-2-includes-the-k-system.html

>> 2. Set the gain of the soundcard to 0 dB,
> Done
>> 3. Adjust the gain of the power amp to the maximum volume
>> you'd ever expect for this tyoe of music. 
> Done
>> 4. If you want to avoid an analog gaing control use a software
>> gain control (preferred), or the ALSA gain setting as your
>> volume control.
> You mean individual application volume controls as opposed to the sound
> card mixer is preferred?
> 
>> If the gain setting of the card has any impact on the magnitude
>> or phase response then simply the card is out of spec.
>> If the gain control of the power amp has any impact on the same,
>> again it's probably out of spec.
>>
>> As long as you don't overload anything, there should be no difference.
>> Things like 'fuller bass' are impossible to comment on. If in doubt,
>> *measure* it.
> So even though turning down the apps volume control theoretically
> reduces the resolution of the sound it should have no bearing on the
> quality of the sound presented? 

Reducing resolution always reduces the quality - some music just needs
to be played loud! :)

As long as you stay in the digital domain, gain changes will not effect
frequency or phase of the sound. But unless you have pro & high-quality
equipment: the analog part (soundcard, amp, speakers) does in practice
respond differently at different gain levels.

Niles Mayer recently elaborated on that:
http://lists.linuxaudio.org/pipermail/linux-audio-user/2010-June/070249.html

> Or do software controls not do that at all?

As long as you stay in the digital domain (here: software) it'll be
"perfect".

Cheers!
robin

> Thanks for the help Fons. I appreciate it and your fine software as
> always.
>