linuxaudio.org

On 06/19/2010 01:57 AM, Bearcat M. Şandor wrote:

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> On Fri, 2010-06-18 at 22:41 +0200, fons@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

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>> 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

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> 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

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> 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,

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> 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....
> 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

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> always.

>

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